This specification is not final and is subject to change. Use is subject to license terms.

Java Debug Wire Protocol Details

VirtualMachine Command Set (1)

Version Command (1)

Returns the JDWP version implemented by the target VM. The version string format is implementation dependent.
Out Data
(None)
Reply Data
Type Name Description
string description Text information on the VM version 
int jdwpMajor Major JDWP Version number 
int jdwpMinor Minor JDWP Version number 
string vmVersion Target VM JRE version, as in the java.version property 
string vmName Target VM name, as in the java.vm.name property 
Error Data
Value Description
VM_DEADThe virtual machine is not running. 

ClassesBySignature Command (2)

Returns reference types for all the classes loaded by the target VM which match the given signature. Multple reference types will be returned if two or more class loaders have loaded a class of the same name. The search is confined to loaded classes only; no attempt is made to load a class of the given signature.
Out Data
Type Name Description
string signature JNI signature of the class to find (for example, "Ljava/lang/String;").  
Reply Data
Type Name Description
int classes Number of reference types that follow. 
Repeated classes times:
byte
refTypeTag Kind of following reference type.  
referenceTypeID
typeID Matching loaded reference type 
int
status The current class status.  
Error Data
Value Description
VM_DEADThe virtual machine is not running. 

AllClasses Command (3)

Returns reference types for all classes currently loaded by the target VM. See JVM TI GetLoadedClasses.
Out Data
(None)
Reply Data
Type Name Description
int classes Number of reference types that follow. 
Repeated classes times:
byte
refTypeTag Kind of following reference type.  
referenceTypeID
typeID Loaded reference type 
string
signature The JNI signature of the loaded reference type 
int
status The current class status.  
Error Data
Value Description
VM_DEADThe virtual machine is not running. 

AllThreads Command (4)

Returns the live platform threads in the target VM. The returned list contains all live platform threads that are attached to the VM. It does not contain virtual threads. The returned list contains platform threads created with the java.lang.Thread API and all native threads attached to the target VM through JNI. Threads that have not yet been started and threads that have completed their execution are not included in the returned list.
Out Data
(None)
Reply Data
Type Name Description
int threads Number of threads that follow. 
Repeated threads times:
threadID
thread A running thread 
Error Data
Value Description
VM_DEADThe virtual machine is not running. 

TopLevelThreadGroups Command (5)

Returns all thread groups that do not have a parent. This command may be used as the first step in building a tree (or trees) of the existing thread groups.
Out Data
(None)
Reply Data
Type Name Description
int groups Number of thread groups that follow. 
Repeated groups times:
threadGroupID
group A top level thread group 
Error Data
Value Description
VM_DEADThe virtual machine is not running. 

Dispose Command (6)

Invalidates this virtual machine mirror. The communication channel to the target VM is closed, and the target VM prepares to accept another subsequent connection from this debugger or another debugger, including the following tasks: Any current method invocations executing in the target VM are continued after the disconnection. Upon completion of any such method invocation, the invoking thread continues from the location where it was originally stopped.

Resources originating in this VirtualMachine (ObjectReferences, ReferenceTypes, etc.) will become invalid.

Out Data
(None)
Reply Data
(None)
Error Data
(None)

IDSizes Command (7)

Returns the sizes of variably-sized data types in the target VM.The returned values indicate the number of bytes used by the identifiers in command and reply packets.
Out Data
(None)
Reply Data
Type Name Description
int fieldIDSize fieldID size in bytes  
int methodIDSize methodID size in bytes  
int objectIDSize objectID size in bytes  
int referenceTypeIDSize referenceTypeID size in bytes  
int frameIDSize frameID size in bytes  
Error Data
Value Description
VM_DEADThe virtual machine is not running. 

Suspend Command (8)

Suspends the execution of the application running in the target VM. All Java threads currently running will be suspended.

Unlike java.lang.Thread.suspend, suspends of both the virtual machine and individual threads are counted. Before a thread will run again, it must be resumed through the VM-level resume command or the thread-level resume command the same number of times it has been suspended.

Out Data
(None)
Reply Data
(None)
Error Data
Value Description
VM_DEADThe virtual machine is not running. 

Resume Command (9)

Resumes execution of the application after the suspend command or an event has stopped it. Suspensions of the Virtual Machine and individual threads are counted. If a particular thread is suspended n times, it must resumed n times before it will continue.
Out Data
(None)
Reply Data
(None)
Error Data
(None)

Exit Command (10)

Terminates the target VM with the given exit code. On some platforms, the exit code might be truncated, for example, to the low order 8 bits. All ids previously returned from the target VM become invalid. Threads running in the VM are abruptly terminated. A thread death exception is not thrown and finally blocks are not run.
Out Data
Type Name Description
int exitCode the exit code 
Reply Data
(None)
Error Data
(None)

CreateString Command (11)

Creates a new string object in the target VM and returns its id.
Out Data
Type Name Description
string utf UTF-8 characters to use in the created string.  
Reply Data
Type Name Description
stringID stringObject Created string (instance of java.lang.String)  
Error Data
Value Description
VM_DEADThe virtual machine is not running. 

Capabilities Command (12)

Retrieve this VM's capabilities. The capabilities are returned as booleans, each indicating the presence or absence of a capability. The commands associated with each capability will return the NOT_IMPLEMENTED error if the cabability is not available.
Out Data
(None)
Reply Data
Type Name Description
boolean canWatchFieldModification Can the VM watch field modification, and therefore can it send the Modification Watchpoint Event? 
boolean canWatchFieldAccess Can the VM watch field access, and therefore can it send the Access Watchpoint Event? 
boolean canGetBytecodes Can the VM get the bytecodes of a given method?  
boolean canGetSyntheticAttribute Can the VM determine whether a field or method is synthetic? (that is, can the VM determine if the method or the field was invented by the compiler?)  
boolean canGetOwnedMonitorInfo Can the VM get the owned monitors infornation for a thread? 
boolean canGetCurrentContendedMonitor Can the VM get the current contended monitor of a thread? 
boolean canGetMonitorInfo Can the VM get the monitor information for a given object?  
Error Data
Value Description
VM_DEADThe virtual machine is not running. 

ClassPaths Command (13)

Retrieve the classpath and bootclasspath of the target VM. If the classpath is not defined, returns an empty list. If the bootclasspath is not defined returns an empty list.
Out Data
(None)
Reply Data
Type Name Description
string baseDir Base directory used to resolve relative paths in either of the following lists. 
int classpaths Number of paths in classpath. 
Repeated classpaths times:
string
path One component of classpath 
int bootclasspaths Number of paths in bootclasspath. 
Repeated bootclasspaths times:
string
path One component of bootclasspath 
Error Data
Value Description
VM_DEADThe virtual machine is not running. 

DisposeObjects Command (14)

Releases a list of object IDs. For each object in the list, the following applies. The count of references held by the back-end (the reference count) will be decremented by refCnt. If thereafter the reference count is less than or equal to zero, the ID is freed. Any back-end resources associated with the freed ID may be freed, and if garbage collection was disabled for the object, it will be re-enabled. The sender of this command promises that no further commands will be sent referencing a freed ID.

Use of this command is not required. If it is not sent, resources associated with each ID will be freed by the back-end at some time after the corresponding object is garbage collected. It is most useful to use this command to reduce the load on the back-end if a very large number of objects has been retrieved from the back-end (a large array, for example) but may not be garbage collected any time soon.

IDs may be re-used by the back-end after they have been freed with this command.This description assumes reference counting, a back-end may use any implementation which operates equivalently.

Out Data
Type Name Description
int requests Number of object dispose requests that follow 
Repeated requests times:
objectID
object The object ID 
int
refCnt The number of times this object ID has been part of a packet received from the back-end. An accurate count prevents the object ID from being freed on the back-end if it is part of an incoming packet, not yet handled by the front-end. 
Reply Data
(None)
Error Data
(None)

HoldEvents Command (15)

Tells the target VM to stop sending events. Events are not discarded; they are held until a subsequent ReleaseEvents command is sent. This command is useful to control the number of events sent to the debugger VM in situations where very large numbers of events are generated. While events are held by the debugger back-end, application execution may be frozen by the debugger back-end to prevent buffer overflows on the back end.Responses to commands are never held and are not affected by thiscommand. If events are already being held, this command is ignored.
Out Data
(None)
Reply Data
(None)
Error Data
(None)

ReleaseEvents Command (16)

Tells the target VM to continue sending events. This command is used to restore normal activity after a HoldEvents command. If there is no current HoldEvents command in effect, this command is ignored.
Out Data
(None)
Reply Data
(None)
Error Data
(None)

CapabilitiesNew Command (17)

Retrieve all of this VM's capabilities. The capabilities are returned as booleans, each indicating the presence or absence of a capability. The commands associated with each capability will return the NOT_IMPLEMENTED error if the cabability is not available.Since JDWP version 1.4.
Out Data
(None)
Reply Data
Type Name Description
boolean canWatchFieldModification Can the VM watch field modification, and therefore can it send the Modification Watchpoint Event? 
boolean canWatchFieldAccess Can the VM watch field access, and therefore can it send the Access Watchpoint Event? 
boolean canGetBytecodes Can the VM get the bytecodes of a given method?  
boolean canGetSyntheticAttribute Can the VM determine whether a field or method is synthetic? (that is, can the VM determine if the method or the field was invented by the compiler?)  
boolean canGetOwnedMonitorInfo Can the VM get the owned monitors infornation for a thread? 
boolean canGetCurrentContendedMonitor Can the VM get the current contended monitor of a thread? 
boolean canGetMonitorInfo Can the VM get the monitor information for a given object?  
boolean canRedefineClasses Can the VM redefine classes? 
boolean canAddMethod Can the VM add methods when redefining classes?

@Deprecated(since="15") A JVM TI based JDWP back-end will never set this capability to true. 

boolean canUnrestrictedlyRedefineClasses Can the VM redefine classes in ways that are normally restricted?

@Deprecated(since="15") A JVM TI based JDWP back-end will never set this capability to true. 

boolean canPopFrames Can the VM pop stack frames? 
boolean canUseInstanceFilters Can the VM filter events by specific object? 
boolean canGetSourceDebugExtension Can the VM get the source debug extension? 
boolean canRequestVMDeathEvent Can the VM request VM death events? 
boolean canSetDefaultStratum Can the VM set a default stratum? 
boolean canGetInstanceInfo Can the VM return instances, counts of instances of classes and referring objects? 
boolean canRequestMonitorEvents Can the VM request monitor events? 
boolean canGetMonitorFrameInfo Can the VM get monitors with frame depth info? 
boolean canUseSourceNameFilters Can the VM filter class prepare events by source name? 
boolean canGetConstantPool Can the VM return the constant pool information? 
boolean canForceEarlyReturn Can the VM force early return from a method? 
boolean supportsVirtualThreads Does the VM support virtual threads, temporary capability 
boolean reserved23 Reserved for future capability 
boolean reserved24 Reserved for future capability 
boolean reserved25 Reserved for future capability 
boolean reserved26 Reserved for future capability 
boolean reserved27 Reserved for future capability 
boolean reserved28 Reserved for future capability 
boolean reserved29 Reserved for future capability 
boolean reserved30 Reserved for future capability 
boolean reserved31 Reserved for future capability 
boolean reserved32 Reserved for future capability 
Error Data
Value Description
VM_DEADThe virtual machine is not running. 

RedefineClasses Command (18)

Installs new class definitions. If there are active stack frames in methods of the redefined classes in the target VM then those active frames continue to run the bytecodes of the original method. These methods are considered obsolete - see IsObsolete. The methods in the redefined classes will be used for new invokes in the target VM. The original method ID refers to the redefined method. All breakpoints in the redefined classes are cleared.If resetting of stack frames is desired, the PopFrames command can be used to pop frames with obsolete methods.

Unless the canUnrestrictedlyRedefineClasses capability is present the redefinition must follow the restrictions described in JVM TI RedefineClasses.

Requires canRedefineClasses capability - see CapabilitiesNew.

@Deprecated(since="15") In addition to the canRedefineClasses capability, the target VM must have the canAddMethod capability to add methods when redefining classes, or the canUnrestrictedlyRedefineClasses capability to redefine classes in ways that are normally restricted.

Out Data
Type Name Description
int classes Number of reference types that follow. 
Repeated classes times:
referenceTypeID
refType The reference type. 
int
classfile Number of bytes defining class (below) 
Repeated classfile times:
byte
classbyte byte in JVM class file format. 
Reply Data
(None)
Error Data
Value Description
INVALID_CLASSOne of the refTypes is not the ID of a reference type. 
INVALID_OBJECTOne of the refTypes is not a known ID. 
UNSUPPORTED_VERSIONA class file has a version number not supported by this VM. 
INVALID_CLASS_FORMATThe virtual machine attempted to read a class file and determined that the file is malformed or otherwise cannot be interpreted as a class file. 
CIRCULAR_CLASS_DEFINITIONA circularity has been detected while initializing a class. 
FAILS_VERIFICATIONThe verifier detected that a class file, though well formed, contained some sort of internal inconsistency or security problem. 
NAMES_DONT_MATCHThe class name defined in the new class file is different from the name in the old class object. 
NOT_IMPLEMENTEDNo aspect of this functionality is implemented (CapabilitiesNew.canRedefineClasses is false) 
ADD_METHOD_NOT_IMPLEMENTEDAdding methods has not been implemented. 
SCHEMA_CHANGE_NOT_IMPLEMENTEDSchema change has not been implemented. 
HIERARCHY_CHANGE_NOT_IMPLEMENTEDA direct superclass is different for the new class version, or the set of directly implemented interfaces is different and canUnrestrictedlyRedefineClasses is false. 
DELETE_METHOD_NOT_IMPLEMENTEDThe new class version does not declare a method declared in the old class version and canUnrestrictedlyRedefineClasses is false. 
CLASS_MODIFIERS_CHANGE_NOT_IMPLEMENTEDThe new class version has different modifiers and canUnrestrictedlyRedefineClasses is false. 
METHOD_MODIFIERS_CHANGE_NOT_IMPLEMENTEDA method in the new class version has different modifiers than its counterpart in the old class version and canUnrestrictedlyRedefineClasses is false. 
CLASS_ATTRIBUTE_CHANGE_NOT_IMPLEMENTEDThe new class version has a different NestHost, NestMembers, PermittedSubclasses, or Record class attribute and canUnrestrictedlyRedefineClasses is false. 
VM_DEADThe virtual machine is not running. 

SetDefaultStratum Command (19)

Set the default stratum. Requires canSetDefaultStratum capability - see CapabilitiesNew.
Out Data
Type Name Description
string stratumID default stratum, or empty string to use reference type default. 
Reply Data
(None)
Error Data
Value Description
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

AllClassesWithGeneric Command (20)

Returns reference types for all classes currently loaded by the target VM. Both the JNI signature and the generic signature are returned for each class. Generic signatures are described in the signature attribute section in The Java Virtual Machine Specification. Since JDWP version 1.5.
Out Data
(None)
Reply Data
Type Name Description
int classes Number of reference types that follow. 
Repeated classes times:
byte
refTypeTag Kind of following reference type.  
referenceTypeID
typeID Loaded reference type 
string
signature The JNI signature of the loaded reference type. 
string
genericSignature The generic signature of the loaded reference type or an empty string if there is none. 
int
status The current class status.  
Error Data
Value Description
VM_DEADThe virtual machine is not running. 

InstanceCounts Command (21)

Returns the number of instances of each reference type in the input list. Only instances that are reachable for the purposes of garbage collection are counted. If a reference type is invalid, eg. it has been unloaded, zero is returned for its instance count.

Since JDWP version 1.6. Requires canGetInstanceInfo capability - see CapabilitiesNew.

Out Data
Type Name Description
int refTypesCount Number of reference types that follow. Must be non-negative. 
Repeated refTypesCount times:
referenceTypeID
refType A reference type ID. 
Reply Data
Type Name Description
int counts The number of counts that follow. 
Repeated counts times:
long
instanceCount The number of instances for the corresponding reference type in 'Out Data'. 
Error Data
Value Description
ILLEGAL_ARGUMENTrefTypesCount is less than zero. 
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

AllModules Command (22)

Returns all modules in the target VM.

Since JDWP version 9.

Out Data
(None)
Reply Data
Type Name Description
int modules The number of the modules that follow. 
Repeated modules times:
moduleID
module One of the modules. 
Error Data
Value Description
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

ReferenceType Command Set (2)

Signature Command (1)

Returns the type signature of a reference type. Type signature formats are the same as specified in JVM TI GetClassSignature.
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
Reply Data
Type Name Description
string signature The JNI signature for the reference type. 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
VM_DEADThe virtual machine is not running. 

ClassLoader Command (2)

Returns the instance of java.lang.ClassLoader which loaded a given reference type. If the reference type was loaded by the system class loader, the returned object ID is null.
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
Reply Data
Type Name Description
classLoaderID classLoader The class loader for the reference type.  
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
VM_DEADThe virtual machine is not running. 

Modifiers Command (3)

Returns the modifiers (also known as access flags) for a reference type. The returned bit mask contains information on the declaration of the reference type. If the reference type is an array or a primitive class (for example, java.lang.Integer.TYPE), the value of the returned bit mask is undefined.
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
Reply Data
Type Name Description
int modBits Modifier bits as defined in Chapter 4 of The Java Virtual Machine Specification 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
VM_DEADThe virtual machine is not running. 

Fields Command (4)

Returns information for each field in a reference type. Inherited fields are not included. The field list will include any synthetic fields created by the compiler. Fields are returned in the order they occur in the class file.
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
Reply Data
Type Name Description
int declared Number of declared fields. 
Repeated declared times:
fieldID
fieldID Field ID. 
string
name Name of field. 
string
signature JNI Signature of field. 
int
modBits The modifier bit flags (also known as access flags) which provide additional information on the field declaration. Individual flag values are defined in Chapter 4 of The Java Virtual Machine Specification. In addition, The 0xf0000000 bit identifies the field as synthetic, if the synthetic attribute capability is available. 
Error Data
Value Description
CLASS_NOT_PREPAREDClass has been loaded but not yet prepared. 
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
VM_DEADThe virtual machine is not running. 

Methods Command (5)

Returns information for each method in a reference type. Inherited methods are not included. The list of methods will include constructors (identified with the name "<init>"), the initialization method (identified with the name "<clinit>") if present, and any synthetic methods created by the compiler. Methods are returned in the order they occur in the class file.
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
Reply Data
Type Name Description
int declared Number of declared methods. 
Repeated declared times:
methodID
methodID Method ID. 
string
name Name of method. 
string
signature JNI signature of method. 
int
modBits The modifier bit flags (also known as access flags) which provide additional information on the method declaration. Individual flag values are defined in Chapter 4 of The Java Virtual Machine Specification. In addition, The 0xf0000000 bit identifies the method as synthetic, if the synthetic attribute capability is available. 
Error Data
Value Description
CLASS_NOT_PREPAREDClass has been loaded but not yet prepared. 
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
VM_DEADThe virtual machine is not running. 

GetValues Command (6)

Returns the value of one or more static fields of the reference type. Each field must be member of the reference type or one of its superclasses, superinterfaces, or implemented interfaces. Access control is not enforced; for example, the values of private fields can be obtained.
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
int fields The number of values to get 
Repeated fields times:
fieldID
fieldID A field to get 
Reply Data
Type Name Description
int values The number of values returned, always equal to fields, the number of values to get. 
Repeated values times:
value
value The field value 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
INVALID_FIELDIDInvalid field. 
VM_DEADThe virtual machine is not running. 

SourceFile Command (7)

Returns the name of source file in which a reference type was declared.
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
Reply Data
Type Name Description
string sourceFile The source file name. No path information for the file is included 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
ABSENT_INFORMATIONThe source file attribute is absent. 
VM_DEADThe virtual machine is not running. 

NestedTypes Command (8)

Returns the classes and interfaces directly nested within this type.Types further nested within those types are not included.
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
Reply Data
Type Name Description
int classes The number of nested classes and interfaces 
Repeated classes times:
byte
refTypeTag Kind of following reference type.  
referenceTypeID
typeID The nested class or interface ID. 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
VM_DEADThe virtual machine is not running. 

Status Command (9)

Returns the current status of the reference type. The status indicates the extent to which the reference type has been initialized, as described in section 2.1.6 of The Java Virtual Machine Specification. If the class is linked the PREPARED and VERIFIED bits in the returned status bits will be set. If the class is initialized the INITIALIZED bit in the returned status bits will be set. If an error occured during initialization then the ERROR bit in the returned status bits will be set. The returned status bits are undefined for array types and for primitive classes (such as java.lang.Integer.TYPE).
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
Reply Data
Type Name Description
int status Status bits:See JDWP.ClassStatus 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
VM_DEADThe virtual machine is not running. 

Interfaces Command (10)

Returns the interfaces declared as implemented by this class. Interfaces indirectly implemented (extended by the implemented interface or implemented by a superclass) are not included.
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
Reply Data
Type Name Description
int interfaces The number of implemented interfaces 
Repeated interfaces times:
interfaceID
interfaceType implemented interface. 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
VM_DEADThe virtual machine is not running. 

ClassObject Command (11)

Returns the class object corresponding to this type.
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
Reply Data
Type Name Description
classObjectID classObject class object. 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
VM_DEADThe virtual machine is not running. 

SourceDebugExtension Command (12)

Returns the value of the SourceDebugExtension attribute. Since JDWP version 1.4. Requires canGetSourceDebugExtension capability - see CapabilitiesNew.
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
Reply Data
Type Name Description
string extension extension attribute 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
ABSENT_INFORMATIONIf the extension is not specified. 
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

SignatureWithGeneric Command (13)

Returns the JNI signature of a reference type along with the generic signature if there is one. Generic signatures are described in the signature attribute section in The Java Virtual Machine Specification. Since JDWP version 1.5.
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
Reply Data
Type Name Description
string signature The JNI signature for the reference type. 
string genericSignature The generic signature for the reference type or an empty string if there is none. 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
VM_DEADThe virtual machine is not running. 

FieldsWithGeneric Command (14)

Returns information, including the generic signature if any, for each field in a reference type. Inherited fields are not included. The field list will include any synthetic fields created by the compiler. Fields are returned in the order they occur in the class file. Generic signatures are described in the signature attribute section in The Java Virtual Machine Specification. Since JDWP version 1.5.
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
Reply Data
Type Name Description
int declared Number of declared fields. 
Repeated declared times:
fieldID
fieldID Field ID. 
string
name The name of the field. 
string
signature The JNI signature of the field. 
string
genericSignature The generic signature of the field, or an empty string if there is none. 
int
modBits The modifier bit flags (also known as access flags) which provide additional information on the field declaration. Individual flag values are defined in Chapter 4 of The Java Virtual Machine Specification. In addition, The 0xf0000000 bit identifies the field as synthetic, if the synthetic attribute capability is available. 
Error Data
Value Description
CLASS_NOT_PREPAREDClass has been loaded but not yet prepared. 
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
VM_DEADThe virtual machine is not running. 

MethodsWithGeneric Command (15)

Returns information, including the generic signature if any, for each method in a reference type. Inherited methodss are not included. The list of methods will include constructors (identified with the name "<init>"), the initialization method (identified with the name "<clinit>") if present, and any synthetic methods created by the compiler. Methods are returned in the order they occur in the class file. Generic signatures are described in the signature attribute section in The Java Virtual Machine Specification. Since JDWP version 1.5.
Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
Reply Data
Type Name Description
int declared Number of declared methods. 
Repeated declared times:
methodID
methodID Method ID. 
string
name The name of the method. 
string
signature The JNI signature of the method. 
string
genericSignature The generic signature of the method, or an empty string if there is none. 
int
modBits The modifier bit flags (also known as access flags) which provide additional information on the method declaration. Individual flag values are defined in Chapter 4 of The Java Virtual Machine Specification. In addition, The 0xf0000000 bit identifies the method as synthetic, if the synthetic attribute capability is available. 
Error Data
Value Description
CLASS_NOT_PREPAREDClass has been loaded but not yet prepared. 
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
VM_DEADThe virtual machine is not running. 

Instances Command (16)

Returns instances of this reference type. Only instances that are reachable for the purposes of garbage collection are returned.

Since JDWP version 1.6. Requires canGetInstanceInfo capability - see CapabilitiesNew.

Out Data
Type Name Description
referenceTypeID refType The reference type ID. 
int maxInstances Maximum number of instances to return. Must be non-negative. If zero, all instances are returned. 
Reply Data
Type Name Description
int instances The number of instances that follow. 
Repeated instances times:
tagged-objectID
instance An instance of this reference type. 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
ILLEGAL_ARGUMENTmaxInstances is less than zero. 
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

ClassFileVersion Command (17)

Returns the class file major and minor version numbers, as defined in the class file format of the Java Virtual Machine specification.

Since JDWP version 1.6.

Out Data
Type Name Description
referenceTypeID refType The class. 
Reply Data
Type Name Description
int majorVersion Major version number 
int minorVersion Minor version number 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
ABSENT_INFORMATIONThe class file version information is absent for primitive and array types. 
VM_DEADThe virtual machine is not running. 

ConstantPool Command (18)

Return the raw bytes of the constant pool in the format of the constant_pool item of the Class File Format in The Java Virtual Machine Specification.

Since JDWP version 1.6. Requires canGetConstantPool capability - see CapabilitiesNew.

Out Data
Type Name Description
referenceTypeID refType The class. 
Reply Data
Type Name Description
int count Total number of constant pool entries plus one. This corresponds to the constant_pool_count item of the Class File Format in The Java Virtual Machine Specification.  
int bytes  
Repeated bytes times:
byte
cpbytes Raw bytes of constant pool 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
NOT_IMPLEMENTEDIf the target virtual machine does not support the retrieval of constant pool information. 
ABSENT_INFORMATIONThe Constant Pool information is absent for primitive and array types. 
VM_DEADThe virtual machine is not running. 

Module Command (19)

Returns the module that this reference type belongs to.

Since JDWP version 9.

Out Data
Type Name Description
referenceTypeID refType The reference type. 
Reply Data
Type Name Description
moduleID module The module this reference type belongs to. 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

ClassType Command Set (3)

Superclass Command (1)

Returns the immediate superclass of a class.
Out Data
Type Name Description
classID clazz The class type ID. 
Reply Data
Type Name Description
classID superclass The superclass (null if the class ID for java.lang.Object is specified). 
Error Data
Value Description
INVALID_CLASSclazz is not the ID of a class. 
INVALID_OBJECTclazz is not a known ID. 
VM_DEADThe virtual machine is not running. 

SetValues Command (2)

Sets the value of one or more static fields. Each field must be member of the class type or one of its superclasses, superinterfaces, or implemented interfaces. Access control is not enforced; for example, the values of private fields can be set. Final fields cannot be set.For primitive values, the value's type must match the field's type exactly. For object values, there must exist a widening reference conversion from the value's type to thefield's type and the field's type must be loaded.
Out Data
Type Name Description
classID clazz The class type ID. 
int values The number of fields to set. 
Repeated values times:
fieldID
fieldID Field to set. 
untagged-value
value Value to put in the field. 
Reply Data
(None)
Error Data
Value Description
INVALID_CLASSclazz is not the ID of a class. 
CLASS_NOT_PREPAREDClass has been loaded but not yet prepared. 
INVALID_OBJECTclazz is not a known ID or a value of an object field is not a known ID. 
INVALID_FIELDIDInvalid field. 
VM_DEADThe virtual machine is not running. 

InvokeMethod Command (3)

Invokes a static method. The method must be member of the class type or one of its superclasses. Access control is not enforced; for example, private methods can be invoked.

The method invocation will occur in the specified thread. Method invocation can occur only if the specified thread has been suspended by an event. Method invocation is not supported when the target VM has been suspended by the front-end.

The specified method is invoked with the arguments in the specified argument list. The method invocation is synchronous; the reply packet is not sent until the invoked method returns in the target VM. The return value (possibly the void value) is included in the reply packet. If the invoked method throws an exception, the exception object ID is set in the reply packet; otherwise, the exception object ID is null.

For primitive arguments, the argument value's type must match the argument's type exactly. For object arguments, there must exist a widening reference conversion from the argument value's type to the argument's type and the argument's type must be loaded.

By default, all threads in the target VM are resumed while the method is being invoked if they were previously suspended by an event or by command. This is done to prevent the deadlocks that will occur if any of the threads own monitors that will be needed by the invoked method. It is possible that breakpoints or other events might occur during the invocation. Note, however, that this implicit resume acts exactly like the ThreadReference resume command, so if the thread's suspend count is greater than 1, it will remain in a suspended state during the invocation. By default, when the invocation completes, all threads in the target VM are suspended, regardless their state before the invocation.

The resumption of other threads during the invoke can be prevented by specifying the INVOKE_SINGLE_THREADED bit flag in the options field; however, there is no protection against or recovery from the deadlocks described above, so this option should be used with great caution. Only the specified thread will be resumed (as described for all threads above). Upon completion of a single threaded invoke, the invoking thread will be suspended once again. Note that any threads started during the single threaded invocation will not be suspended when the invocation completes.

If the target VM is disconnected during the invoke (for example, through the VirtualMachine dispose command) the method invocation continues.

Out Data
Type Name Description
classID clazz The class type ID. 
threadID thread The thread in which to invoke. 
methodID methodID The method to invoke. 
int arguments  
Repeated arguments times:
value
arg The argument value. 
int options Invocation options 
Reply Data
Type Name Description
value returnValue The returned value. 
tagged-objectID exception The thrown exception. 
Error Data
Value Description
INVALID_CLASSclazz is not the ID of a class. 
INVALID_OBJECTclazz is not a known ID. 
INVALID_METHODIDmethodID is not the ID of a static method in this class type or one of its superclasses. 
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
THREAD_NOT_SUSPENDEDIf the specified thread has not been suspended by an event. 
VM_DEADThe virtual machine is not running. 

NewInstance Command (4)

Creates a new object of this type, invoking the specified constructor. The constructor method ID must be a member of the class type.

Instance creation will occur in the specified thread. Instance creation can occur only if the specified thread has been suspended by an event. Method invocation is not supported when the target VM has been suspended by the front-end.

The specified constructor is invoked with the arguments in the specified argument list. The constructor invocation is synchronous; the reply packet is not sent until the invoked method returns in the target VM. The return value (possibly the void value) is included in the reply packet. If the constructor throws an exception, the exception object ID is set in the reply packet; otherwise, the exception object ID is null.

For primitive arguments, the argument value's type must match the argument's type exactly. For object arguments, there must exist a widening reference conversion from the argument value's type to the argument's type and the argument's type must be loaded.

By default, all threads in the target VM are resumed while the method is being invoked if they were previously suspended by an event or by command. This is done to prevent the deadlocks that will occur if any of the threads own monitors that will be needed by the invoked method. It is possible that breakpoints or other events might occur during the invocation. Note, however, that this implicit resume acts exactly like the ThreadReference resume command, so if the thread's suspend count is greater than 1, it will remain in a suspended state during the invocation. By default, when the invocation completes, all threads in the target VM are suspended, regardless their state before the invocation.

The resumption of other threads during the invoke can be prevented by specifying the INVOKE_SINGLE_THREADED bit flag in the options field; however, there is no protection against or recovery from the deadlocks described above, so this option should be used with great caution. Only the specified thread will be resumed (as described for all threads above). Upon completion of a single threaded invoke, the invoking thread will be suspended once again. Note that any threads started during the single threaded invocation will not be suspended when the invocation completes.

If the target VM is disconnected during the invoke (for example, through the VirtualMachine dispose command) the method invocation continues.

Out Data
Type Name Description
classID clazz The class type ID. 
threadID thread The thread in which to invoke the constructor. 
methodID methodID The constructor to invoke. 
int arguments  
Repeated arguments times:
value
arg The argument value. 
int options Constructor invocation options 
Reply Data
Type Name Description
tagged-objectID newObject The newly created object, or null if the constructor threw an exception. 
tagged-objectID exception The thrown exception, if any; otherwise, null. 
Error Data
Value Description
INVALID_CLASSclazz is not the ID of a class. 
INVALID_OBJECTclazz is not a known ID or a value of an object parameter is not a known ID.. 
INVALID_METHODIDmethodID is not the ID of a method. 
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
THREAD_NOT_SUSPENDEDIf the specified thread has not been suspended by an event. 
VM_DEADThe virtual machine is not running. 

ArrayType Command Set (4)

NewInstance Command (1)

Creates a new array object of this type with a given length.
Out Data
Type Name Description
arrayTypeID arrType The array type of the new instance. 
int length The length of the array. 
Reply Data
Type Name Description
tagged-objectID newArray The newly created array object.  
Error Data
Value Description
INVALID_ARRAYThe array is invalid. 
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
VM_DEADThe virtual machine is not running. 

InterfaceType Command Set (5)

InvokeMethod Command (1)

Invokes a static method. The method must not be a static initializer. The method must be a member of the interface type.

Since JDWP version 1.8

The method invocation will occur in the specified thread. Method invocation can occur only if the specified thread has been suspended by an event. Method invocation is not supported when the target VM has been suspended by the front-end.

The specified method is invoked with the arguments in the specified argument list. The method invocation is synchronous; the reply packet is not sent until the invoked method returns in the target VM. The return value (possibly the void value) is included in the reply packet. If the invoked method throws an exception, the exception object ID is set in the reply packet; otherwise, the exception object ID is null.

For primitive arguments, the argument value's type must match the argument's type exactly. For object arguments, there must exist a widening reference conversion from the argument value's type to the argument's type and the argument's type must be loaded.

By default, all threads in the target VM are resumed while the method is being invoked if they were previously suspended by an event or by a command. This is done to prevent the deadlocks that will occur if any of the threads own monitors that will be needed by the invoked method. It is possible that breakpoints or other events might occur during the invocation. Note, however, that this implicit resume acts exactly like the ThreadReference resume command, so if the thread's suspend count is greater than 1, it will remain in a suspended state during the invocation. By default, when the invocation completes, all threads in the target VM are suspended, regardless their state before the invocation.

The resumption of other threads during the invoke can be prevented by specifying the INVOKE_SINGLE_THREADED bit flag in the options field; however, there is no protection against or recovery from the deadlocks described above, so this option should be used with great caution. Only the specified thread will be resumed (as described for all threads above). Upon completion of a single threaded invoke, the invoking thread will be suspended once again. Note that any threads started during the single threaded invocation will not be suspended when the invocation completes.

If the target VM is disconnected during the invoke (for example, through the VirtualMachine dispose command) the method invocation continues.

Out Data
Type Name Description
interfaceID clazz The interface type ID. 
threadID thread The thread in which to invoke. 
methodID methodID The method to invoke. 
int arguments  
Repeated arguments times:
value
arg The argument value. 
int options Invocation options 
Reply Data
Type Name Description
value returnValue The returned value. 
tagged-objectID exception The thrown exception. 
Error Data
Value Description
INVALID_CLASSclazz is not the ID of an interface. 
INVALID_OBJECTclazz is not a known ID. 
INVALID_METHODIDmethodID is not the ID of a static method in this interface type or is the ID of a static initializer. 
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
THREAD_NOT_SUSPENDEDIf the specified thread has not been suspended by an event. 
VM_DEADThe virtual machine is not running. 

Method Command Set (6)

LineTable Command (1)

Returns line number information for the method, if present. The line table maps source line numbers to the initial code index of the line. The line table is ordered by code index (from lowest to highest). The line number information is constant unless a new class definition is installed using RedefineClasses.
Out Data
Type Name Description
referenceTypeID refType The class. 
methodID methodID The method. 
Reply Data
Type Name Description
long start Lowest valid code index for the method, >=0, or -1 if the method is native  
long end Highest valid code index for the method, >=0, or -1 if the method is native 
int lines The number of entries in the line table for this method. 
Repeated lines times:
long
lineCodeIndex Initial code index of the line, start <= lineCodeIndex < end 
int
lineNumber Line number. 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
INVALID_METHODIDmethodID is not the ID of a method. 
VM_DEADThe virtual machine is not running. 

VariableTable Command (2)

Returns variable information for the method. The variable table includes arguments and locals declared within the method. For instance methods, the "this" reference is included in the table. Also, synthetic variables may be present.
Out Data
Type Name Description
referenceTypeID refType The class. 
methodID methodID The method. 
Reply Data
Type Name Description
int argCnt The number of words in the frame used by arguments. Eight-byte arguments use two words; all others use one.  
int slots The number of variables. 
Repeated slots times:
long
codeIndex First code index at which the variable is visible (unsigned). Used in conjunction with length. The variable can be get or set only when the current codeIndex <= current frame code index < codeIndex + length  
string
name The variable's name. 
string
signature The variable type's JNI signature. 
int
length Unsigned value used in conjunction with codeIndex. The variable can be get or set only when the current codeIndex <= current frame code index < code index + length  
int
slot The local variable's index in its frame 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
INVALID_METHODIDmethodID is not the ID of a method. 
ABSENT_INFORMATIONthere is no variable information for the method. 
VM_DEADThe virtual machine is not running. 

Bytecodes Command (3)

Retrieve the method's bytecodes as defined in The Java Virtual Machine Specification. Requires canGetBytecodes capability - see CapabilitiesNew.
Out Data
Type Name Description
referenceTypeID refType The class. 
methodID methodID The method. 
Reply Data
Type Name Description
int bytes  
Repeated bytes times:
byte
bytecode A Java bytecode. 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
INVALID_METHODIDmethodID is not the ID of a method. 
NOT_IMPLEMENTEDIf the target virtual machine does not support the retrieval of bytecodes. 
VM_DEADThe virtual machine is not running. 

IsObsolete Command (4)

Determine if this method is obsolete. A method is obsolete if it has been replaced by a non-equivalent method using the RedefineClasses command. The original and redefined methods are considered equivalent if their bytecodes are the same except for indices into the constant pool and the referenced constants are equal.
Out Data
Type Name Description
referenceTypeID refType The class. 
methodID methodID The method. 
Reply Data
Type Name Description
boolean isObsolete true if this method has been replacedby a non-equivalent method usingthe RedefineClasses command. 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
INVALID_METHODIDmethodID is not the ID of a method. 
NOT_IMPLEMENTEDIf the target virtual machine does not support this query. 
VM_DEADThe virtual machine is not running. 

VariableTableWithGeneric Command (5)

Returns variable information for the method, including generic signatures for the variables. The variable table includes arguments and locals declared within the method. For instance methods, the "this" reference is included in the table. Also, synthetic variables may be present. Generic signatures are described in the signature attribute section in The Java Virtual Machine Specification. Since JDWP version 1.5.
Out Data
Type Name Description
referenceTypeID refType The class. 
methodID methodID The method. 
Reply Data
Type Name Description
int argCnt The number of words in the frame used by arguments. Eight-byte arguments use two words; all others use one.  
int slots The number of variables. 
Repeated slots times:
long
codeIndex First code index at which the variable is visible (unsigned). Used in conjunction with length. The variable can be get or set only when the current codeIndex <= current frame code index < codeIndex + length  
string
name The variable's name. 
string
signature The variable type's JNI signature. 
string
genericSignature The variable type's generic signature or an empty string if there is none. 
int
length Unsigned value used in conjunction with codeIndex. The variable can be get or set only when the current codeIndex <= current frame code index < code index + length  
int
slot The local variable's index in its frame 
Error Data
Value Description
INVALID_CLASSrefType is not the ID of a reference type. 
INVALID_OBJECTrefType is not a known ID. 
INVALID_METHODIDmethodID is not the ID of a method. 
ABSENT_INFORMATIONthere is no variable information for the method. 
VM_DEADThe virtual machine is not running. 

Field Command Set (8)

ObjectReference Command Set (9)

ReferenceType Command (1)

Returns the runtime type of the object. The runtime type will be a class or an array.
Out Data
Type Name Description
objectID object The object ID 
Reply Data
Type Name Description
byte refTypeTag Kind of following reference type.  
referenceTypeID typeID The runtime reference type. 
Error Data
Value Description
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
VM_DEADThe virtual machine is not running. 

GetValues Command (2)

Returns the value of one or more instance fields. Each field must be member of the object's type or one of its superclasses, superinterfaces, or implemented interfaces. Access control is not enforced; for example, the values of private fields can be obtained.
Out Data
Type Name Description
objectID object The object ID 
int fields The number of values to get 
Repeated fields times:
fieldID
fieldID Field to get. 
Reply Data
Type Name Description
int values The number of values returned, always equal to 'fields', the number of values to get. Field values are ordered in the reply in the same order as corresponding fieldIDs in the command. 
Repeated values times:
value
value The field value 
Error Data
Value Description
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
INVALID_FIELDIDInvalid field. 
VM_DEADThe virtual machine is not running. 

SetValues Command (3)

Sets the value of one or more instance fields. Each field must be member of the object's type or one of its superclasses, superinterfaces, or implemented interfaces. Access control is not enforced; for example, the values of private fields can be set. For primitive values, the value's type must match the field's type exactly. For object values, there must be a widening reference conversion from the value's type to thefield's type and the field's type must be loaded.
Out Data
Type Name Description
objectID object The object ID 
int values The number of fields to set. 
Repeated values times:
fieldID
fieldID Field to set. 
untagged-value
value Value to put in the field. 
Reply Data
(None)
Error Data
Value Description
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
INVALID_FIELDIDInvalid field. 
VM_DEADThe virtual machine is not running. 

MonitorInfo Command (5)

Returns monitor information for an object. All threads int the VM must be suspended.Requires canGetMonitorInfo capability - see CapabilitiesNew.
Out Data
Type Name Description
objectID object The object ID 
Reply Data
Type Name Description
threadID owner The monitor owner, or null if it is not currently owned. 
int entryCount The number of times the monitor has been entered. 
int waiters The number of threads that are waiting for the monitor 0 if there is no current owner 
Repeated waiters times:
threadID
thread A thread waiting for this monitor. 
Error Data
Value Description
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

InvokeMethod Command (6)

Invokes a instance method. The method must be member of the object's type or one of its superclasses, superinterfaces, or implemented interfaces. Access control is not enforced; for example, private methods can be invoked.

The method invocation will occur in the specified thread. Method invocation can occur only if the specified thread has been suspended by an event. Method invocation is not supported when the target VM has been suspended by the front-end.

The specified method is invoked with the arguments in the specified argument list. The method invocation is synchronous; the reply packet is not sent until the invoked method returns in the target VM. The return value (possibly the void value) is included in the reply packet. If the invoked method throws an exception, the exception object ID is set in the reply packet; otherwise, the exception object ID is null.

For primitive arguments, the argument value's type must match the argument's type exactly. For object arguments, there must be a widening reference conversion from the argument value's type to the argument's type and the argument's type must be loaded.

By default, all threads in the target VM are resumed while the method is being invoked if they were previously suspended by an event or by a command. This is done to prevent the deadlocks that will occur if any of the threads own monitors that will be needed by the invoked method. It is possible that breakpoints or other events might occur during the invocation. Note, however, that this implicit resume acts exactly like the ThreadReference resume command, so if the thread's suspend count is greater than 1, it will remain in a suspended state during the invocation. By default, when the invocation completes, all threads in the target VM are suspended, regardless their state before the invocation.

The resumption of other threads during the invoke can be prevented by specifying the INVOKE_SINGLE_THREADED bit flag in the options field; however, there is no protection against or recovery from the deadlocks described above, so this option should be used with great caution. Only the specified thread will be resumed (as described for all threads above). Upon completion of a single threaded invoke, the invoking thread will be suspended once again. Note that any threads started during the single threaded invocation will not be suspended when the invocation completes.

If the target VM is disconnected during the invoke (for example, through the VirtualMachine dispose command) the method invocation continues.

Out Data
Type Name Description
objectID object The object ID 
threadID thread The thread in which to invoke. 
classID clazz The class type. 
methodID methodID The method to invoke. 
int arguments The number of arguments. 
Repeated arguments times:
value
arg The argument value. 
int options Invocation options 
Reply Data
Type Name Description
value returnValue The returned value, or null if an exception is thrown. 
tagged-objectID exception The thrown exception, if any. 
Error Data
Value Description
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
INVALID_CLASSclazz is not the ID of a reference type. 
INVALID_METHODIDmethodID is not the ID of an instance method in this object's type or one of its superclasses, superinterfaces, or implemented interfaces. 
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
THREAD_NOT_SUSPENDEDIf the specified thread has not been suspended by an event. 
VM_DEADThe virtual machine is not running. 

DisableCollection Command (7)

Prevents garbage collection for the given object. By default all objects in back-end replies may be collected at any time the target VM is running. A call to this command guarantees that the object will not be collected. The EnableCollection command can be used to allow collection once again.

Note that while the target VM is suspended, no garbage collection will occur because all threads are suspended. The typical examination of variables, fields, and arrays during the suspension is safe without explicitly disabling garbage collection.

This method should be used sparingly, as it alters the pattern of garbage collection in the target VM and, consequently, may result in application behavior under the debugger that differs from its non-debugged behavior.

Out Data
Type Name Description
objectID object The object ID 
Reply Data
(None)
Error Data
Value Description
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
VM_DEADThe virtual machine is not running. 

EnableCollection Command (8)

Permits garbage collection for this object. By default all objects returned by JDWP may become unreachable in the target VM, and hence may be garbage collected. A call to this command is necessary only if garbage collection was previously disabled with the DisableCollection command.
Out Data
Type Name Description
objectID object The object ID 
Reply Data
(None)
Error Data
Value Description
VM_DEADThe virtual machine is not running. 

IsCollected Command (9)

Determines whether an object has been garbage collected in the target VM.
Out Data
Type Name Description
objectID object The object ID 
Reply Data
Type Name Description
boolean isCollected true if the object has been collected; false otherwise 
Error Data
Value Description
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
VM_DEADThe virtual machine is not running. 

ReferringObjects Command (10)

Returns objects that directly reference this object. Only objects that are reachable for the purposes of garbage collection are returned. Note that an object can also be referenced in other ways, such as from a local variable in a stack frame, or from a JNI global reference. Such non-object referrers are not returned by this command.

Since JDWP version 1.6. Requires canGetInstanceInfo capability - see CapabilitiesNew.

Out Data
Type Name Description
objectID object The object ID 
int maxReferrers Maximum number of referring objects to return. Must be non-negative. If zero, all referring objects are returned. 
Reply Data
Type Name Description
int referringObjects The number of objects that follow. 
Repeated referringObjects times:
tagged-objectID
instance An object that references this object. 
Error Data
Value Description
INVALID_OBJECTobject is not a known ID. 
ILLEGAL_ARGUMENTmaxReferrers is less than zero. 
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

StringReference Command Set (10)

Value Command (1)

Returns the characters contained in the string.
Out Data
Type Name Description
objectID stringObject The String object ID.  
Reply Data
Type Name Description
string stringValue UTF-8 representation of the string value. 
Error Data
Value Description
INVALID_STRINGThe string is invalid. 
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
VM_DEADThe virtual machine is not running. 

ThreadReference Command Set (11)

Name Command (1)

Returns the thread name.
Out Data
Type Name Description
threadID thread The thread object ID.  
Reply Data
Type Name Description
string threadName The thread name. 
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTthread is not a known ID. 
VM_DEADThe virtual machine is not running. 

Suspend Command (2)

Suspends the thread.

Unlike java.lang.Thread.suspend(), suspends of both the virtual machine and individual threads are counted. Before a thread will run again, it must be resumed the same number of times it has been suspended.

Suspending single threads with command has the same dangers java.lang.Thread.suspend(). If the suspended thread holds a monitor needed by another running thread, deadlock is possible in the target VM (at least until the suspended thread is resumed again).

The suspended thread is guaranteed to remain suspended until resumed through one of the JDI resume methods mentioned above; the application in the target VM cannot resume the suspended thread through {@link java.lang.Thread#resume}.

Note that this doesn't change the status of the thread (see the ThreadStatus command.) For example, if it was Running, it will still appear running to other threads.

Out Data
Type Name Description
threadID thread The thread object ID.  
Reply Data
(None)
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTthread is not a known ID. 
VM_DEADThe virtual machine is not running. 

Resume Command (3)

Resumes the execution of a given thread. If this thread was not previously suspended by the front-end, calling this command has no effect. Otherwise, the count of pending suspends on this thread is decremented. If it is decremented to 0, the thread will continue to execute.
Out Data
Type Name Description
threadID thread The thread object ID.  
Reply Data
(None)
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTthread is not a known ID. 
VM_DEADThe virtual machine is not running. 

Status Command (4)

Returns the current status of a thread. The thread status reply indicates the thread status the last time it was running. the suspend status provides information on the thread's suspension, if any.
Out Data
Type Name Description
threadID thread The thread object ID.  
Reply Data
Type Name Description
int threadStatus One of the thread status codes See JDWP.ThreadStatus 
int suspendStatus One of the suspend status codes See JDWP.SuspendStatus 
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTthread is not a known ID. 
VM_DEADThe virtual machine is not running. 

ThreadGroup Command (5)

Returns the thread group that contains a given thread.
Out Data
Type Name Description
threadID thread The thread object ID.  
Reply Data
Type Name Description
threadGroupID group The thread group of this thread.  
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTthread is not a known ID. 
VM_DEADThe virtual machine is not running. 

Frames Command (6)

Returns the current call stack of a suspended thread. The sequence of frames starts with the currently executing frame, followed by its caller, and so on. The thread must be suspended, and the returned frameID is valid only while the thread is suspended.
Out Data
Type Name Description
threadID thread The thread object ID.  
int startFrame The index of the first frame to retrieve. 
int length The count of frames to retrieve (-1 means all remaining).  
Reply Data
Type Name Description
int frames The number of frames retreived 
Repeated frames times:
frameID
frameID The ID of this frame.  
location
location The current location of this frame 
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTthread is not a known ID. 
VM_DEADThe virtual machine is not running. 

FrameCount Command (7)

Returns the count of frames on this thread's stack. The thread must be suspended, and the returned count is valid only while the thread is suspended. Returns JDWP.Error.errorThreadNotSuspended if not suspended.
Out Data
Type Name Description
threadID thread The thread object ID.  
Reply Data
Type Name Description
int frameCount The count of frames on this thread's stack.  
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTthread is not a known ID. 
VM_DEADThe virtual machine is not running. 

OwnedMonitors Command (8)

Returns the objects whose monitors have been entered by this thread. The thread must be suspended, and the returned information is relevant only while the thread is suspended. Requires canGetOwnedMonitorInfo capability - see CapabilitiesNew.
Out Data
Type Name Description
threadID thread The thread object ID.  
Reply Data
Type Name Description
int owned The number of owned monitors 
Repeated owned times:
tagged-objectID
monitor An owned monitor 
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTthread is not a known ID. 
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

CurrentContendedMonitor Command (9)

Returns the object, if any, for which this thread is waiting. The thread may be waiting to enter a monitor, or it may be waiting, via the java.lang.Object.wait method, for another thread to invoke the notify method. The thread must be suspended, and the returned information is relevant only while the thread is suspended. Requires canGetCurrentContendedMonitor capability - see CapabilitiesNew.
Out Data
Type Name Description
threadID thread The thread object ID.  
Reply Data
Type Name Description
tagged-objectID monitor The contended monitor, or null if there is no current contended monitor.  
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTthread is not a known ID. 
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

Stop Command (10)

Stops the thread with an asynchronous exception.
Out Data
Type Name Description
threadID thread The thread object ID.  
objectID throwable Asynchronous exception. This object must be an instance of java.lang.Throwable or a subclass 
Reply Data
(None)
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTIf thread is not a known ID or the asynchronous exception has been garbage collected. 
VM_DEADThe virtual machine is not running. 

Interrupt Command (11)

Interrupt the thread, as if done by java.lang.Thread.interrupt
Out Data
Type Name Description
threadID thread The thread object ID.  
Reply Data
(None)
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTthread is not a known ID. 
VM_DEADThe virtual machine is not running. 

SuspendCount Command (12)

Get the suspend count for this thread. The suspend count is the number of times the thread has been suspended through the thread-level or VM-level suspend commands without a corresponding resume
Out Data
Type Name Description
threadID thread The thread object ID.  
Reply Data
Type Name Description
int suspendCount The number of outstanding suspends of this thread.  
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTthread is not a known ID. 
VM_DEADThe virtual machine is not running. 

OwnedMonitorsStackDepthInfo Command (13)

Returns monitor objects owned by the thread, along with stack depth at which the monitor was acquired. Returns stack depth of -1 if the implementation cannot determine the stack depth (e.g., for monitors acquired by JNI MonitorEnter).The thread must be suspended, and the returned information is relevant only while the thread is suspended. Requires canGetMonitorFrameInfo capability - see CapabilitiesNew.

Since JDWP version 1.6.

Out Data
Type Name Description
threadID thread The thread object ID.  
Reply Data
Type Name Description
int owned The number of owned monitors 
Repeated owned times:
tagged-objectID
monitor An owned monitor 
int
stack_depth Stack depth location where monitor was acquired 
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTthread is not a known ID. 
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

ForceEarlyReturn Command (14)

Force a method to return before it reaches a return statement.

The method which will return early is referred to as the called method. The called method is the current method (as defined by the Frames section in The Java Virtual Machine Specification) for the specified thread at the time this command is received.

The specified thread must be suspended. The return occurs when execution of Java programming language code is resumed on this thread. Between sending this command and resumption of thread execution, the state of the stack is undefined.

No further instructions are executed in the called method. Specifically, finally blocks are not executed. Note: this can cause inconsistent states in the application.

A lock acquired by calling the called method (if it is a synchronized method) and locks acquired by entering synchronized blocks within the called method are released. Note: this does not apply to JNI locks or java.util.concurrent.locks locks.

Events, such as MethodExit, are generated as they would be in a normal return.

The called method must be a non-native Java programming language method. Forcing return on a thread with only one frame on the stack causes the thread to exit when resumed.

For void methods, the value must be a void value. For methods that return primitive values, the value's type must match the return type exactly. For object values, there must be a widening reference conversion from the value's type to the return type type and the return type must be loaded.

Since JDWP version 1.6. Requires canForceEarlyReturn capability - see CapabilitiesNew.

Out Data
Type Name Description
threadID thread The thread object ID.  
value value The value to return.  
Reply Data
(None)
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTThread or value is not a known ID. 
THREAD_NOT_SUSPENDEDIf the specified thread has not been suspended by an event. 
THREAD_NOT_ALIVEThread has not been started or is now dead. 
OPAQUE_FRAMEAttempted to return early from a frame corresponding to a native method. Or the implementation is unable to provide this functionality on this frame. 
NO_MORE_FRAMESThere are no more Java or JNI frames on the call stack. 
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
TYPE_MISMATCHValue is not an appropriate type for the return value of the method. 
VM_DEADThe virtual machine is not running. 

IsVirtual Command (15)

Determine if a thread is a virtual thread.
Out Data
Type Name Description
threadID thread The thread object ID. 
Reply Data
Type Name Description
boolean isVirtual true if the thread is a virtual thread. 
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTthread is not a known ID. 
VM_DEADThe virtual machine is not running. 

ThreadGroupReference Command Set (12)

Name Command (1)

Returns the thread group name.
Out Data
Type Name Description
threadGroupID group The thread group object ID.  
Reply Data
Type Name Description
string groupName The thread group's name. 
Error Data
Value Description
INVALID_THREAD_GROUPThread group invalid. 
INVALID_OBJECTgroup is not a known ID. 
VM_DEADThe virtual machine is not running. 

Parent Command (2)

Returns the thread group, if any, which contains a given thread group.
Out Data
Type Name Description
threadGroupID group The thread group object ID.  
Reply Data
Type Name Description
threadGroupID parentGroup The parent thread group object, or null if the given thread group is a top-level thread group 
Error Data
Value Description
INVALID_THREAD_GROUPThread group invalid. 
INVALID_OBJECTgroup is not a known ID. 
VM_DEADThe virtual machine is not running. 

Children Command (3)

Returns the live threads and active thread groups directly contained in this thread group. Virtual threads are not considered live threads in a thread group and are not included. Threads and thread groups in child thread groups are not included. A thread is alive if it has been started and has not yet been stopped. See java.lang.ThreadGroup for information about active ThreadGroups.
Out Data
Type Name Description
threadGroupID group The thread group object ID.  
Reply Data
Type Name Description
int childThreads The number of live child threads.  
Repeated childThreads times:
threadID
childThread A direct child thread ID.  
int childGroups The number of active child thread groups.  
Repeated childGroups times:
threadGroupID
childGroup A direct child thread group ID.  
Error Data
Value Description
INVALID_THREAD_GROUPThread group invalid. 
INVALID_OBJECTgroup is not a known ID. 
VM_DEADThe virtual machine is not running. 

ArrayReference Command Set (13)

Length Command (1)

Returns the number of components in a given array.
Out Data
Type Name Description
arrayID arrayObject The array object ID.  
Reply Data
Type Name Description
int arrayLength The length of the array. 
Error Data
Value Description
INVALID_OBJECTarrayObject is not a known ID. 
INVALID_ARRAYThe array is invalid. 
VM_DEADThe virtual machine is not running. 

GetValues Command (2)

Returns a range of array components. The specified range must be within the bounds of the array.
Out Data
Type Name Description
arrayID arrayObject The array object ID.  
int firstIndex The first index to retrieve. 
int length The number of components to retrieve. 
Reply Data
Type Name Description
arrayregion values The retrieved values. If the values are objects, they are tagged-values; otherwise, they are untagged-values 
Error Data
Value Description
INVALID_LENGTHIf index is beyond the end of this array. 
INVALID_OBJECTarrayObject is not a known ID. 
INVALID_ARRAYThe array is invalid. 
VM_DEADThe virtual machine is not running. 

SetValues Command (3)

Sets a range of array components. The specified range must be within the bounds of the array. For primitive values, each value's type must match the array component type exactly. For object values, there must be a widening reference conversion from the value's type to thearray component type and the array component type must be loaded.
Out Data
Type Name Description
arrayID arrayObject The array object ID.  
int firstIndex The first index to set. 
int values The number of values to set.  
Repeated values times:
untagged-value
value A value to set.  
Reply Data
(None)
Error Data
Value Description
INVALID_LENGTHIf index is beyond the end of this array. 
INVALID_OBJECTarrayObject is not a known ID. 
INVALID_ARRAYThe array is invalid. 
VM_DEADThe virtual machine is not running. 

ClassLoaderReference Command Set (14)

VisibleClasses Command (1)

Returns a list of all classes which this class loader can find by name via ClassLoader::loadClass, Class::forName and bytecode linkage. That is, all classes for which this class loader has been recorded as an initiating loader. The list contains each reference type created by this loader and any types for which loading was delegated by this class loader to another class loader.

The visible class list has useful properties with respect to the type namespace. A particular type name will occur at most once in the list. Each field or variable declared with that type name in a class defined by this class loader must be resolved to that single type.

No ordering of the returned list is guaranteed.

See JVM TI GetClassLoaderClasses.

Out Data
Type Name Description
classLoaderID classLoaderObject The class loader object ID.  
Reply Data
Type Name Description
int classes The number of visible classes.  
Repeated classes times:
byte
refTypeTag Kind of following reference type.  
referenceTypeID
typeID A class visible to this class loader. 
Error Data
Value Description
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
INVALID_CLASS_LOADERThe class loader is invalid. 
VM_DEADThe virtual machine is not running. 

EventRequest Command Set (15)

Set Command (1)

Set an event request. When the event described by this request occurs, an event is sent from the target VM. If an event occurs that has not been requested then it is not sent from the target VM. The two exceptions to this are the VM Start Event and the VM Death Event which are automatically generated events - see Composite Command for further details.
Out Data
Type Name Description
byte eventKind Event kind to request. See JDWP.EventKind for a complete list of events that can be requested; some events may require a capability in order to be requested.  
byte suspendPolicy What threads are suspended when this event occurs? Note that the order of events and command replies accurately reflects the order in which threads are suspended and resumed. For example, if a VM-wide resume is processed before an event occurs which suspends the VM, the reply to the resume command will be written to the transport before the suspending event. 
int modifiers Constraints used to control the number of generated events.Modifiers specify additional tests that an event must satisfy before it is placed in the event queue. Events are filtered by applying each modifier to an event in the order they are specified in this collection Only events that satisfy all modifiers are reported. A value of 0 means there are no modifiers in the request.

Filtering can improve debugger performance dramatically byreducing the amount of event traffic sent from the target VM to the debugger VM.  

Repeated modifiers times:
byte
modKind Modifier kind 
Case Count - if modKind is 1:
Limit the requested event to be reported at most once after a given number of occurrences. The event is not reported the first count - 1 times this filter is reached. To request a one-off event, call this method with a count of 1.

Once the count reaches 0, any subsequent filters in this request are applied. If none of those filters cause the event to be suppressed, the event is reported. Otherwise, the event is not reported. In either case subsequent events are never reported for this request. This modifier can be used with any event kind. 

int
count Count before event. One for one-off. 
Case Conditional - if modKind is 2:
Conditional on expression 
int
exprID For the future 
Case ThreadOnly - if modKind is 3:
Restricts reported events to those in the given thread. This modifier can be used with any event kind except for class unload.  
threadID
thread Required thread 
Case ClassOnly - if modKind is 4:
For class prepare events, restricts the events generated by this request to be the preparation of the given reference type and any subtypes. For monitor wait and waited events, restricts the events generated by this request to those whose monitor object is of the given reference type or any of its subtypes. For other events, restricts the events generated by this request to those whose location is in the given reference type or any of its subtypes. An event will be generated for any location in a reference type that can be safely cast to the given reference type. This modifier can be used with any event kind except class unload, thread start, and thread end.  
referenceTypeID
clazz Required class 
Case ClassMatch - if modKind is 5:
Restricts reported events to those for classes whose name matches the given restricted regular expression. For class prepare events, the prepared class name is matched. For class unload events, the unloaded class name is matched. For monitor wait and waited events, the name of the class of the monitor object is matched. For other events, the class name of the event's location is matched. This modifier can be used with any event kind except thread start and thread end.  
string
classPattern Required class pattern. Matches are limited to exact matches of the given class pattern and matches of patterns that begin or end with '*'; for example, "*.Foo" or "java.*".  
Case ClassExclude - if modKind is 6:
Restricts reported events to those for classes whose name does not match the given restricted regular expression. For class prepare events, the prepared class name is matched. For class unload events, the unloaded class name is matched. For monitor wait and waited events, the name of the class of the monitor object is matched. For other events, the class name of the event's location is matched. This modifier can be used with any event kind except thread start and thread end.  
string
classPattern Disallowed class pattern. Matches are limited to exact matches of the given class pattern and matches of patterns that begin or end with '*'; for example, "*.Foo" or "java.*".  
Case LocationOnly - if modKind is 7:
Restricts reported events to those that occur at the given location. This modifier can be used with breakpoint, field access, field modification, step, and exception event kinds.  
location
loc Required location 
Case ExceptionOnly - if modKind is 8:
Restricts reported exceptions by their class and whether they are caught or uncaught. This modifier can be used with exception event kinds only.  
referenceTypeID
exceptionOrNull Exception to report. Null (0) means report exceptions of all types. A non-null type restricts the reported exception events to exceptions of the given type or any of its subtypes.  
boolean
caught Report caught exceptions 
boolean
uncaught Report uncaught exceptions. Note that it is not always possible to determine whether an exception is caught or uncaught at the time it is thrown. See the exception event catch location under composite events for more information.  
Case FieldOnly - if modKind is 9:
Restricts reported events to those that occur for a given field. This modifier can be used with field access and field modification event kinds only.  
referenceTypeID
declaring Type in which field is declared. 
fieldID
fieldID Required field 
Case Step - if modKind is 10:
Restricts reported step events to those which satisfy depth and size constraints. This modifier can be used with step event kinds only.  
threadID
thread Thread in which to step 
int
size size of each step. See JDWP.StepSize 
int
depth relative call stack limit. See JDWP.StepDepth 
Case InstanceOnly - if modKind is 11:
Restricts reported events to those whose active 'this' object is the given object. Match value is the null object for static methods. This modifier can be used with any event kind except class prepare, class unload, thread start, and thread end. Introduced in JDWP version 1.4. 
objectID
instance Required 'this' object 
Case SourceNameMatch - if modKind is 12:
Restricts reported class prepare events to those for reference types which have a source name which matches the given restricted regular expression. The source names are determined by the reference type's SourceDebugExtension. This modifier can only be used with class prepare events. Since JDWP version 1.6. Requires the canUseSourceNameFilters capability - see CapabilitiesNew
string
sourceNamePattern Required source name pattern. Matches are limited to exact matches of the given pattern and matches of patterns that begin or end with '*'; for example, "*.Foo" or "java.*".  
Case PlatformThreadsOnly - if modKind is 13:
For thread start and thread end events, restrict the events so they are only sent for platform threads. 
Reply Data
Type Name Description
int requestID ID of created request 
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_CLASSInvalid class. 
INVALID_STRINGThe string is invalid. 
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
INVALID_COUNTThe count is invalid. 
INVALID_FIELDIDInvalid field. 
INVALID_METHODIDInvalid method. 
INVALID_LOCATIONInvalid location. 
INVALID_EVENT_TYPEThe specified event type id is not recognized. 
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

Clear Command (2)

Clear an event request. See JDWP.EventKind for a complete list of events that can be cleared. Only the event request matching the specified event kind and requestID is cleared. If there isn't a matching event request the command is a no-op and does not result in an error. Automatically generated events do not have a corresponding event request and may not be cleared using this command.
Out Data
Type Name Description
byte eventKind Event kind to clear 
int requestID ID of request to clear 
Reply Data
(None)
Error Data
Value Description
VM_DEADThe virtual machine is not running. 
INVALID_EVENT_TYPEThe specified event type id is not recognized. 

ClearAllBreakpoints Command (3)

Removes all set breakpoints, a no-op if there are no breakpoints set.
Out Data
(None)
Reply Data
(None)
Error Data
Value Description
VM_DEADThe virtual machine is not running. 

StackFrame Command Set (16)

GetValues Command (1)

Returns the value of one or more local variables in a given frame. Each variable must be visible at the frame's code index. Even if local variable information is not available, values can be retrieved if the front-end is able to determine the correct local variable index. (Typically, this index can be determined for method arguments from the method signature without access to the local variable table information.)
Out Data
Type Name Description
threadID thread The frame's thread.  
frameID frame The frame ID.  
int slots The number of values to get.  
Repeated slots times:
int
slot The local variable's index in the frame.  
byte
sigbyte A tag identifying the type of the variable  
Reply Data
Type Name Description
int values The number of values retrieved, always equal to slots, the number of values to get. 
Repeated values times:
value
slotValue The value of the local variable.  
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
INVALID_FRAMEIDInvalid jframeID. 
INVALID_SLOTInvalid slot. 
VM_DEADThe virtual machine is not running. 

SetValues Command (2)

Sets the value of one or more local variables. Each variable must be visible at the current frame code index. For primitive values, the value's type must match the variable's type exactly. For object values, there must be a widening reference conversion from the value's type to thevariable's type and the variable's type must be loaded.

Even if local variable information is not available, values can be set, if the front-end is able to determine the correct local variable index. (Typically, thisindex can be determined for method arguments from the method signature without access to the local variable table information.)

Out Data
Type Name Description
threadID thread The frame's thread.  
frameID frame The frame ID.  
int slotValues The number of values to set.  
Repeated slotValues times:
int
slot The slot ID.  
value
slotValue The value to set.  
Reply Data
(None)
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
INVALID_FRAMEIDInvalid jframeID. 
VM_DEADThe virtual machine is not running. 

ThisObject Command (3)

Returns the value of the 'this' reference for this frame. If the frame's method is static or native, the reply will contain the null object reference.
Out Data
Type Name Description
threadID thread The frame's thread.  
frameID frame The frame ID.  
Reply Data
Type Name Description
tagged-objectID objectThis The 'this' object for this frame.  
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
INVALID_FRAMEIDInvalid jframeID. 
VM_DEADThe virtual machine is not running. 

PopFrames Command (4)

Pop the top-most stack frames of the thread stack, up to, and including 'frame'. The thread must be suspended to perform this command. The top-most stack frames are discarded and the stack frame previous to 'frame' becomes the current frame. The operand stack is restored -- the argument values are added back and if the invoke was not invokestatic, objectref is added back as well. The Java virtual machine program counter is restored to the opcode of the invoke instruction.

Since JDWP version 1.4. Requires canPopFrames capability - see CapabilitiesNew.

Out Data
Type Name Description
threadID thread The thread object ID.  
frameID frame The frame ID.  
Reply Data
(None)
Error Data
Value Description
INVALID_THREADPassed thread is null, is not a valid thread or has exited. 
INVALID_OBJECTthread is not a known ID. 
INVALID_FRAMEIDInvalid jframeID. 
THREAD_NOT_SUSPENDEDIf the specified thread has not been suspended by an event. 
NO_MORE_FRAMESThere are no more Java or JNI frames on the call stack. 
INVALID_FRAMEIDInvalid jframeID. 
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

ClassObjectReference Command Set (17)

ReflectedType Command (1)

Returns the reference type reflected by this class object.
Out Data
Type Name Description
classObjectID classObject The class object.  
Reply Data
Type Name Description
byte refTypeTag Kind of following reference type.  
referenceTypeID typeID reflected reference type 
Error Data
Value Description
INVALID_OBJECTIf this reference type has been unloaded and garbage collected. 
VM_DEADThe virtual machine is not running. 

ModuleReference Command Set (18)

Name Command (1)

Returns the name of this module.

Since JDWP version 9.

Out Data
Type Name Description
moduleID module This module. 
Reply Data
Type Name Description
string name The module's name. 
Error Data
Value Description
INVALID_MODULEInvalid module. 
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

ClassLoader Command (2)

Returns the class loader of this module.

Since JDWP version 9.

Out Data
Type Name Description
moduleID module This module. 
Reply Data
Type Name Description
classLoaderID classLoader The module's class loader. 
Error Data
Value Description
INVALID_MODULEInvalid module. 
NOT_IMPLEMENTEDThe functionality is not implemented in this virtual machine. 
VM_DEADThe virtual machine is not running. 

Event Command Set (64)

Composite Command (100)

Several events may occur at a given time in the target VM. For example, there may be more than one breakpoint request for a given location or you might single step to the same location as a breakpoint request. These events are delivered together as a composite event. For uniformity, a composite event is always used to deliver events, even if there is only one event to report.

The events that are grouped in a composite event are restricted in the following ways:

The VM Start Event and VM Death Event are automatically generated events. This means they do not need to be requested using the EventRequest.Set command. The VM Start event signals the completion of VM initialization. The VM Death event signals the termination of the VM.If there is a debugger connected at the time when an automatically generated event occurs it is sent from the target VM. Automatically generated events may also be requested using the EventRequest.Set command and thus multiple events of the same event kind will be sent from the target VM when an event occurs.Automatically generated events are sent with the requestID field in the Event Data set to 0. The value of the suspendPolicy field in the Event Data depends on the event. For the automatically generated VM Start Event the value of suspendPolicy is not defined and is therefore implementation or configuration specific. In the Sun implementation, for example, the suspendPolicy is specified as an option to the JDWP agent at launch-time.The automatically generated VM Death Event will have the suspendPolicy set to NONE.

Event Data
Type Name Description
byte suspendPolicy Which threads where suspended by this composite event? 
int events Events in set. 
Repeated events times:
byte
eventKind Event kind selector 
Case VMStart - if eventKind is JDWP.EventKind.VM_START:
Notification of initialization of a target VM. This event is received before the main thread is started and before any application code has been executed. Before this event occurs a significant amount of system code has executed and a number of system classes have been loaded. This event is always generated by the target VM, even if not explicitly requested. 
int
requestID Request that generated event (or 0 if this event is automatically generated. 
threadID
thread Initial thread 
Case SingleStep - if eventKind is JDWP.EventKind.SINGLE_STEP:
Notification of step completion in the target VM. The step event is generated before the code at its location is executed.  
int
requestID Request that generated event 
threadID
thread Stepped thread 
location
location Location stepped to 
Case Breakpoint - if eventKind is JDWP.EventKind.BREAKPOINT:
Notification of a breakpoint in the target VM. The breakpoint event is generated before the code at its location is executed.  
int
requestID Request that generated event 
threadID
thread Thread which hit breakpoint 
location
location Location hit 
Case MethodEntry - if eventKind is JDWP.EventKind.METHOD_ENTRY:
Notification of a method invocation in the target VM. This event is generated before any code in the invoked method has executed. Method entry events are generated for both native and non-native methods.

In some VMs method entry events can occur for a particular thread before its thread start event occurs if methods are called as part of the thread's initialization.  

int
requestID Request that generated event 
threadID
thread Thread which entered method 
location
location The initial executable location in the method. 
Case MethodExit - if eventKind is JDWP.EventKind.METHOD_EXIT:
Notification of a method return in the target VM. This event is generated after all code in the method has executed, but the location of this event is the last executed location in the method. Method exit events are generated for both native and non-native methods. Method exit events are not generated if the method terminates with a thrown exception.  
int
requestID Request that generated event 
threadID
thread Thread which exited method 
location
location Location of exit 
Case MethodExitWithReturnValue - if eventKind is JDWP.EventKind.METHOD_EXIT_WITH_RETURN_VALUE:
Notification of a method return in the target VM. This event is generated after all code in the method has executed, but the location of this event is the last executed location in the method. Method exit events are generated for both native and non-native methods. Method exit events are not generated if the method terminates with a thrown exception.

Since JDWP version 1.6.  

int
requestID Request that generated event 
threadID
thread Thread which exited method 
location
location Location of exit 
value
value Value that will be returned by the method 
Case MonitorContendedEnter - if eventKind is JDWP.EventKind.MONITOR_CONTENDED_ENTER:
Notification that a thread in the target VM is attempting to enter a monitor that is already acquired by another thread. Requires canRequestMonitorEvents capability - see CapabilitiesNew.

Since JDWP version 1.6.  

int
requestID Request that generated event 
threadID
thread Thread which is trying to enter the monitor 
tagged-objectID
object Monitor object reference 
location
location Location of contended monitor enter 
Case MonitorContendedEntered - if eventKind is JDWP.EventKind.MONITOR_CONTENDED_ENTERED:
Notification of a thread in the target VM is entering a monitor after waiting for it to be released by another thread. Requires canRequestMonitorEvents capability - see CapabilitiesNew.

Since JDWP version 1.6.  

int
requestID Request that generated event 
threadID
thread Thread which entered monitor 
tagged-objectID
object Monitor object reference 
location
location Location of contended monitor enter 
Case MonitorWait - if eventKind is JDWP.EventKind.MONITOR_WAIT:
Notification of a thread about to wait on a monitor object. Requires canRequestMonitorEvents capability - see CapabilitiesNew.

Since JDWP version 1.6.  

int
requestID Request that generated event 
threadID
thread Thread which is about to wait 
tagged-objectID
object Monitor object reference 
location
location Location at which the wait will occur 
long
timeout Thread wait time in milliseconds 
Case MonitorWaited - if eventKind is JDWP.EventKind.MONITOR_WAITED:
Notification that a thread in the target VM has finished waiting on Requires canRequestMonitorEvents capability - see CapabilitiesNew. a monitor object.

Since JDWP version 1.6.  

int
requestID Request that generated event 
threadID
thread Thread which waited 
tagged-objectID
object Monitor object reference 
location
location Location at which the wait occured 
boolean
timed_out True if timed out 
Case Exception - if eventKind is JDWP.EventKind.EXCEPTION:
Notification of an exception in the target VM. If the exception is thrown from a non-native method, the exception event is generated at the location where the exception is thrown. If the exception is thrown from a native method, the exception event is generated at the first non-native location reached after the exception is thrown.  
int
requestID Request that generated event 
threadID
thread Thread with exception 
location
location Location of exception throw (or first non-native location after throw if thrown from a native method) 
tagged-objectID
exception Thrown exception 
location
catchLocation Location of catch, or 0 if not caught. An exception is considered to be caught if, at the point of the throw, the current location is dynamically enclosed in a try statement that handles the exception. (See the JVM specification for details). If there is such a try statement, the catch location is the first location in the appropriate catch clause.

If there are native methods in the call stack at the time of the exception, there are important restrictions to note about the returned catch location. In such cases, it is not possible to predict whether an exception will be handled by some native method on the call stack. Thus, it is possible that exceptions considered uncaught here will, in fact, be handled by a native method and not cause termination of the target VM. Furthermore, it cannot be assumed that the catch location returned here will ever be reached by the throwing thread. If there is a native frame between the current location and the catch location, the exception might be handled and cleared in that native method instead.

Note that compilers can generate try-catch blocks in some cases where they are not explicit in the source code; for example, the code generated for synchronized and finally blocks can contain implicit try-catch blocks. If such an implicitly generated try-catch is present on the call stack at the time of the throw, the exception will be considered caught even though it appears to be uncaught from examination of the source code.  

Case ThreadStart - if eventKind is JDWP.EventKind.THREAD_START:
Notification of a new running thread in the target VM. The new thread can be the result of a call to java.lang.Thread.start or the result of attaching a new thread to the VM though JNI. The notification is generated by the new thread some time before its execution starts. Because of this timing, it is possible to receive other events for the thread before this event is received. (Notably, Method Entry Events and Method Exit Events might occur during thread initialization. It is also possible for the VirtualMachine AllThreads command to return a thread before its thread start event is received.

Note that this event gives no information about the creation of the thread object which may have happened much earlier, depending on the VM being debugged.  

int
requestID Request that generated event 
threadID
thread Started thread 
Case ThreadDeath - if eventKind is JDWP.EventKind.THREAD_DEATH:
Notification of a completed thread in the target VM. The notification is generated by the dying thread before it terminates. Because of this timing, it is possible for {@link VirtualMachine#allThreads} to return this thread after this event is received.

Note that this event gives no information about the lifetime of the thread object. It may or may not be collected soon depending on what references exist in the target VM.  

int
requestID Request that generated event 
threadID
thread Ending thread 
Case ClassPrepare - if eventKind is JDWP.EventKind.CLASS_PREPARE:
Notification of a class prepare in the target VM. See the JVM specification for a definition of class preparation. Class prepare events are not generated for primtiive classes (for example, java.lang.Integer.TYPE).  
int
requestID Request that generated event 
threadID
thread Preparing thread. In rare cases, this event may occur in a debugger system thread within the target VM. Debugger threads take precautions to prevent these events, but they cannot be avoided under some conditions, especially for some subclasses of java.lang.Error. If the event was generated by a debugger system thread, the value returned by this method is null, and if the requested suspend policy for the event was EVENT_THREAD all threads will be suspended instead, and the composite event's suspend policy will reflect this change.

Note that the discussion above does not apply to system threads created by the target VM during its normal (non-debug) operation.  

byte
refTypeTag Kind of reference type. See JDWP.TypeTag 
referenceTypeID
typeID Type being prepared 
string
signature Type signature 
int
status Status of type. See JDWP.ClassStatus 
Case ClassUnload - if eventKind is JDWP.EventKind.CLASS_UNLOAD:
Notification of a class unload in the target VM.

There are severe constraints on the debugger back-end during garbage collection, so unload information is greatly limited.  

int
requestID Request that generated event 
string
signature Type signature 
Case FieldAccess - if eventKind is JDWP.EventKind.FIELD_ACCESS:
Notification of a field access in the target VM. Field modifications are not considered field accesses. Requires canWatchFieldAccess capability - see CapabilitiesNew
int
requestID Request that generated event 
threadID
thread Accessing thread 
location
location Location of access 
byte
refTypeTag Kind of reference type. See JDWP.TypeTag 
referenceTypeID
typeID Type of field 
fieldID
fieldID Field being accessed 
tagged-objectID
object Object being accessed (null=0 for statics 
Case FieldModification - if eventKind is JDWP.EventKind.FIELD_MODIFICATION:
Notification of a field modification in the target VM. Requires canWatchFieldModification capability - see CapabilitiesNew
int
requestID Request that generated event 
threadID
thread Modifying thread 
location
location Location of modify 
byte
refTypeTag Kind of reference type. See JDWP.TypeTag 
referenceTypeID
typeID Type of field 
fieldID
fieldID Field being modified 
tagged-objectID
object Object being modified (null=0 for statics 
value
valueToBe Value to be assigned 
Case VMDeath - if eventKind is JDWP.EventKind.VM_DEATH:
 
int
requestID Request that generated event 

Error Constants

Name Value Description
NONE0No error has occurred. 
INVALID_THREAD10Passed thread is null, is not a valid thread or has exited. 
INVALID_THREAD_GROUP11Thread group invalid. 
INVALID_PRIORITY12Invalid priority. 
THREAD_NOT_SUSPENDED13If the specified thread has not been suspended by an event. 
THREAD_SUSPENDED14Thread already suspended. 
THREAD_NOT_ALIVE15Thread has not been started or is now dead. 
INVALID_OBJECT20If this reference type has been unloaded and garbage collected. 
INVALID_CLASS21Invalid class. 
CLASS_NOT_PREPARED22Class has been loaded but not yet prepared. 
INVALID_METHODID23Invalid method. 
INVALID_LOCATION24Invalid location. 
INVALID_FIELDID25Invalid field. 
INVALID_FRAMEID30Invalid jframeID. 
NO_MORE_FRAMES31There are no more Java or JNI frames on the call stack. 
OPAQUE_FRAME32Information about the frame is not available. 
NOT_CURRENT_FRAME33Operation can only be performed on current frame. 
TYPE_MISMATCH34The variable is not an appropriate type for the function used. 
INVALID_SLOT35Invalid slot. 
DUPLICATE40Item already set. 
NOT_FOUND41Desired element not found. 
INVALID_MODULE42Invalid module. 
INVALID_MONITOR50Invalid monitor. 
NOT_MONITOR_OWNER51This thread doesn't own the monitor. 
INTERRUPT52The call has been interrupted before completion. 
INVALID_CLASS_FORMAT60The virtual machine attempted to read a class file and determined that the file is malformed or otherwise cannot be interpreted as a class file. 
CIRCULAR_CLASS_DEFINITION61A circularity has been detected while initializing a class. 
FAILS_VERIFICATION62The verifier detected that a class file, though well formed, contained some sort of internal inconsistency or security problem. 
ADD_METHOD_NOT_IMPLEMENTED63Adding methods has not been implemented. 
SCHEMA_CHANGE_NOT_IMPLEMENTED64Schema change has not been implemented. 
INVALID_TYPESTATE65The state of the thread has been modified, and is now inconsistent. 
HIERARCHY_CHANGE_NOT_IMPLEMENTED66A direct superclass is different for the new class version, or the set of directly implemented interfaces is different and canUnrestrictedlyRedefineClasses is false. 
DELETE_METHOD_NOT_IMPLEMENTED67The new class version does not declare a method declared in the old class version and canUnrestrictedlyRedefineClasses is false. 
UNSUPPORTED_VERSION68A class file has a version number not supported by this VM. 
NAMES_DONT_MATCH69The class name defined in the new class file is different from the name in the old class object. 
CLASS_MODIFIERS_CHANGE_NOT_IMPLEMENTED70The new class version has different modifiers and canUnrestrictedlyRedefineClasses is false. 
METHOD_MODIFIERS_CHANGE_NOT_IMPLEMENTED71A method in the new class version has different modifiers than its counterpart in the old class version and canUnrestrictedlyRedefineClasses is false. 
CLASS_ATTRIBUTE_CHANGE_NOT_IMPLEMENTED72The new class version has a different NestHost, NestMembers, PermittedSubclasses, or Record class attribute and canUnrestrictedlyRedefineClasses is false. 
NOT_IMPLEMENTED99The functionality is not implemented in this virtual machine. 
NULL_POINTER100Invalid pointer. 
ABSENT_INFORMATION101Desired information is not available. 
INVALID_EVENT_TYPE102The specified event type id is not recognized. 
ILLEGAL_ARGUMENT103Illegal argument. 
OUT_OF_MEMORY110The function needed to allocate memory and no more memory was available for allocation. 
ACCESS_DENIED111Debugging has not been enabled in this virtual machine. JVMTI cannot be used. 
VM_DEAD112The virtual machine is not running. 
INTERNAL113An unexpected internal error has occurred. 
UNATTACHED_THREAD115The thread being used to call this function is not attached to the virtual machine. Calls must be made from attached threads. 
INVALID_TAG500object type id or class tag. 
ALREADY_INVOKING502Previous invoke not complete. 
INVALID_INDEX503Index is invalid. 
INVALID_LENGTH504The length is invalid. 
INVALID_STRING506The string is invalid. 
INVALID_CLASS_LOADER507The class loader is invalid. 
INVALID_ARRAY508The array is invalid. 
TRANSPORT_LOAD509Unable to load the transport. 
TRANSPORT_INIT510Unable to initialize the transport. 
NATIVE_METHOD511 
INVALID_COUNT512The count is invalid. 

EventKind Constants

Name Value Description
SINGLE_STEP1 
BREAKPOINT2 
FRAME_POP3 
EXCEPTION4 
USER_DEFINED5 
THREAD_START6 
THREAD_DEATH7 
THREAD_END7obsolete - was used in jvmdi 
CLASS_PREPARE8 
CLASS_UNLOAD9 
CLASS_LOAD10 
FIELD_ACCESS20 
FIELD_MODIFICATION21 
EXCEPTION_CATCH30 
METHOD_ENTRY40 
METHOD_EXIT41 
METHOD_EXIT_WITH_RETURN_VALUE42 
MONITOR_CONTENDED_ENTER43 
MONITOR_CONTENDED_ENTERED44 
MONITOR_WAIT45 
MONITOR_WAITED46 
VM_START90 
VM_INIT90obsolete - was used in jvmdi 
VM_DEATH99 
VM_DISCONNECTED100Never sent across JDWP 

ThreadStatus Constants

Name Value Description
ZOMBIE0Thread has terminated. 
RUNNING1Thread is runnable. 
SLEEPING2Thread is sleeping, in Thread.sleep. 
MONITOR3Thread is waiting to enter a synchronized block/method or, after an Object.wait, waiting to re-enter a synchronized block/method. 
WAIT4Thread is waiting, in Object.wait or LockSupport.park. A virtual thread that is sleeping in Thread.sleep may have this thread status instead of SLEEPING. 

SuspendStatus Constants

Name Value Description
SUSPEND_STATUS_SUSPENDED0x1 

ClassStatus Constants

Name Value Description
VERIFIED1 
PREPARED2 
INITIALIZED4 
ERROR8 

TypeTag Constants

Name Value Description
CLASS1ReferenceType is a class.  
INTERFACE2ReferenceType is an interface.  
ARRAY3ReferenceType is an array.  

Tag Constants

Name Value Description
ARRAY91'[' - an array object (objectID size).  
BYTE66'B' - a byte value (1 byte). 
CHAR67'C' - a character value (2 bytes). 
OBJECT76'L' - an object (objectID size). 
FLOAT70'F' - a float value (4 bytes). 
DOUBLE68'D' - a double value (8 bytes). 
INT73'I' - an int value (4 bytes). 
LONG74'J' - a long value (8 bytes). 
SHORT83'S' - a short value (2 bytes). 
VOID86'V' - a void value (no bytes). 
BOOLEAN90'Z' - a boolean value (1 byte). 
STRING115's' - a String object (objectID size).  
THREAD116't' - a Thread object (objectID size).  
THREAD_GROUP103'g' - a ThreadGroup object (objectID size).  
CLASS_LOADER108'l' - a ClassLoader object (objectID size).  
CLASS_OBJECT99'c' - a class object object (objectID size).  

StepDepth Constants

Name Value Description
INTO0Step into any method calls that occur before the end of the step.  
OVER1Step over any method calls that occur before the end of the step.  
OUT2Step out of the current method.  

StepSize Constants

Name Value Description
MIN0Step by the minimum possible amount (often a bytecode instruction).  
LINE1Step to the next source line unless there is no line number information in which case a MIN step is done instead. 

SuspendPolicy Constants

Name Value Description
NONE0Suspend no threads when this event is encountered.  
EVENT_THREAD1Suspend the event thread when this event is encountered.  
ALL2Suspend all threads when this event is encountered.  

InvokeOptions Constants

The invoke options are a combination of zero or more of the following bit flags:
Name Value Description
INVOKE_SINGLE_THREADED0x01otherwise, all threads started.  
INVOKE_NONVIRTUAL0x02otherwise, normal virtual invoke (instance methods only)