Class AccessController
The AccessController
class is used for access control operations
and decisions.
More specifically, the AccessController
class is used for
three purposes:
- to decide whether an access to a critical system resource is to be allowed or denied, based on the security policy currently in effect,
- to mark code as being "privileged", thus affecting subsequent access determinations, and
- to obtain a "snapshot" of the current calling context so access-control decisions from a different context can be made with respect to the saved context.
The checkPermission
method
determines whether the access request indicated by a specified
permission should be granted or denied. A sample call appears
below. In this example, checkPermission
will determine
whether or not to grant "read" access to the file named "testFile" in
the "/temp" directory.
FilePermission perm = new FilePermission("/temp/testFile", "read"); AccessController.checkPermission(perm);
If a requested access is allowed,
checkPermission
returns quietly. If denied, an
AccessControlException
is
thrown. AccessControlException
can also be thrown if the requested
permission is of an incorrect type or contains an invalid value.
Such information is given whenever possible.
Suppose the current thread traversed m callers, in the order of caller 1
to caller 2 to caller m. Then caller m invoked the
checkPermission
method.
The checkPermission
method determines whether access
is granted or denied based on the following algorithm:
for (int i = m; i > 0; i--) {
if (caller i's domain does not have the permission)
throw AccessControlException
else if (caller i is marked as privileged) {
if (a context was specified in the call to doPrivileged)
context.checkPermission(permission)
if (limited permissions were specified in the call to doPrivileged) {
for (each limited permission) {
if (the limited permission implies the requested permission)
return;
}
} else
return;
}
}
// Next, check the context inherited when the thread was created.
// Whenever a new thread is created, the AccessControlContext at
// that time is stored and associated with the new thread, as the
// "inherited" context.
inheritedContext.checkPermission(permission);
A caller can be marked as being "privileged"
(see doPrivileged
and below).
When making access control decisions, the checkPermission
method stops checking if it reaches a caller that
was marked as "privileged" via a doPrivileged
call without a context argument (see below for information about a
context argument). If that caller's domain has the
specified permission and at least one limiting permission argument (if any)
implies the requested permission, no further checking is done and
checkPermission
returns quietly, indicating that the requested access is allowed.
If that domain does not have the specified permission, an exception
is thrown, as usual. If the caller's domain had the specified permission
but it was not implied by any limiting permission arguments given in the call
to doPrivileged
then the permission checking continues
until there are no more callers or another doPrivileged
call matches the requested permission and returns normally.
The normal use of the "privileged" feature is as follows. If you don't need to return a value from within the "privileged" block, do the following:
somemethod() {
...normal code here...
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
// privileged code goes here, for example:
System.loadLibrary("awt");
return null; // nothing to return
}
});
...normal code here...
}
PrivilegedAction
is an interface with a single method, named
run
.
The above example shows creation of an implementation
of that interface; a concrete implementation of the
run
method is supplied.
When the call to doPrivileged
is made, an
instance of the PrivilegedAction
implementation is passed
to it. The doPrivileged
method calls the
run
method from the PrivilegedAction
implementation after enabling privileges, and returns the
run
method's return value as the
doPrivileged
return value (which is
ignored in this example).
If you need to return a value, you can do something like the following:
somemethod() {
...normal code here...
String user = AccessController.doPrivileged(
new PrivilegedAction<String>() {
public String run() {
return System.getProperty("user.name");
}
});
...normal code here...
}
If the action performed in your run
method could
throw a "checked" exception (those listed in the throws
clause
of a method), then you need to use the
PrivilegedExceptionAction
interface instead of the
PrivilegedAction
interface:
somemethod() throws FileNotFoundException {
...normal code here...
try {
FileInputStream fis = AccessController.doPrivileged(
new PrivilegedExceptionAction<FileInputStream>() {
public FileInputStream run() throws FileNotFoundException {
return new FileInputStream("someFile");
}
});
} catch (PrivilegedActionException e) {
// e.getException() should be an instance of FileNotFoundException,
// as only "checked" exceptions will be "wrapped" in a
// PrivilegedActionException.
throw (FileNotFoundException) e.getException();
}
...normal code here...
}
Be *very* careful in your use of the "privileged" construct, and
always remember to make the privileged code section as small as possible.
You can pass Permission
arguments to further limit the
scope of the "privilege" (see below).
Note that checkPermission
always performs security checks
within the context of the currently executing thread.
Sometimes a security check that should be made within a given context
will actually need to be done from within a
different context (for example, from within a worker thread).
The getContext
method and
AccessControlContext
class are provided
for this situation. The getContext
method takes a "snapshot"
of the current calling context, and places
it in an AccessControlContext
object, which it returns. A sample call is
the following:
AccessControlContext acc = AccessController.getContext()
AccessControlContext
itself has a checkPermission
method
that makes access decisions based on the context it encapsulates,
rather than that of the current execution thread.
Code within a different context can thus call that method on the
previously-saved AccessControlContext
object. A sample call is the
following:
acc.checkPermission(permission)
There are also times where you don't know a priori which permissions
to check the context against. In these cases you can use the
doPrivileged
method that takes a context. You can also limit the
scope of the privileged code by passing additional Permission
parameters.
somemethod() {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
public Object run() {
// Code goes here. Any permission checks within this
// run method will require that the intersection of the
// caller's protection domain and the snapshot's
// context have the desired permission. If a requested
// permission is not implied by the limiting FilePermission
// argument then checking of the thread continues beyond the
// caller of doPrivileged.
}
}, acc, new FilePermission("/temp/*", read));
...normal code here...
}
Passing a limiting Permission
argument of an instance of
AllPermission
is equivalent to calling the equivalent
doPrivileged
method without limiting Permission
arguments. Passing a zero length array of Permission
disables
the code privileges so that checking always continues beyond the caller of
that doPrivileged
method.
- Since:
- 1.2
- See Also:
-
Method Summary
Modifier and TypeMethodDescriptionstatic void
checkPermission
(Permission perm) Deprecated, for removal: This API element is subject to removal in a future version.Determines whether the access request indicated by the specified permission should be allowed or denied, based on the currentAccessControlContext
and security policy.static <T> T
doPrivileged
(PrivilegedAction<T> action) Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedAction
with privileges enabled.static <T> T
doPrivileged
(PrivilegedAction<T> action, AccessControlContext context) Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedAction
with privileges enabled and restricted by the specifiedAccessControlContext
.static <T> T
doPrivileged
(PrivilegedAction<T> action, AccessControlContext context, Permission... perms) Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedAction
with privileges enabled and restricted by the specifiedAccessControlContext
and with a privilege scope limited by specifiedPermission
arguments.static <T> T
doPrivileged
(PrivilegedExceptionAction<T> action) Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedExceptionAction
with privileges enabled.static <T> T
doPrivileged
(PrivilegedExceptionAction<T> action, AccessControlContext context) Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedExceptionAction
with privileges enabled and restricted by the specifiedAccessControlContext
.static <T> T
doPrivileged
(PrivilegedExceptionAction<T> action, AccessControlContext context, Permission... perms) Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedExceptionAction
with privileges enabled and restricted by the specifiedAccessControlContext
and with a privilege scope limited by specifiedPermission
arguments.static <T> T
doPrivilegedWithCombiner
(PrivilegedAction<T> action) Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedAction
with privileges enabled.static <T> T
doPrivilegedWithCombiner
(PrivilegedAction<T> action, AccessControlContext context, Permission... perms) Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedAction
with privileges enabled and restricted by the specifiedAccessControlContext
and with a privilege scope limited by specifiedPermission
arguments.static <T> T
Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedExceptionAction
with privileges enabled.static <T> T
doPrivilegedWithCombiner
(PrivilegedExceptionAction<T> action, AccessControlContext context, Permission... perms) Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedExceptionAction
with privileges enabled and restricted by the specifiedAccessControlContext
and with a privilege scope limited by specifiedPermission
arguments.static AccessControlContext
Deprecated, for removal: This API element is subject to removal in a future version.This method takes a "snapshot" of the current calling context, which includes the current thread's inheritedAccessControlContext
and any limited privilege scope, and places it in anAccessControlContext
object.
-
Method Details
-
doPrivileged
Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedAction
with privileges enabled. The action is performed with all of the permissions possessed by the caller's protection domain.If the action's
run
method throws an (unchecked) exception, it will propagate through this method.Note that any
DomainCombiner
associated with the currentAccessControlContext
will be ignored while the action is performed.- Type Parameters:
T
- the type of the value returned by the PrivilegedAction'srun
method.- Parameters:
action
- the action to be performed.- Returns:
- the value returned by the action's
run
method. - Throws:
NullPointerException
- if the action isnull
- See Also:
-
doPrivilegedWithCombiner
Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedAction
with privileges enabled. The action is performed with all of the permissions possessed by the caller's protection domain.If the action's
run
method throws an (unchecked) exception, it will propagate through this method.This method preserves the current AccessControlContext's
DomainCombiner
(which may be null) while the action is performed.- Type Parameters:
T
- the type of the value returned by the PrivilegedAction'srun
method.- Parameters:
action
- the action to be performed.- Returns:
- the value returned by the action's
run
method. - Throws:
NullPointerException
- if the action isnull
- Since:
- 1.6
- See Also:
-
doPrivileged
Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedAction
with privileges enabled and restricted by the specifiedAccessControlContext
. The action is performed with the intersection of the permissions possessed by the caller's protection domain, and those possessed by the domains represented by the specifiedAccessControlContext
.If the action's
run
method throws an (unchecked) exception, it will propagate through this method.If a security manager is installed and the specified
AccessControlContext
was not created by system code and the caller'sProtectionDomain
has not been granted the "createAccessControlContext"SecurityPermission
, then the action is performed with no permissions.- Type Parameters:
T
- the type of the value returned by the PrivilegedAction'srun
method.- Parameters:
action
- the action to be performed.context
- an access control context representing the restriction to be applied to the caller's domain's privileges before performing the specified action. If the context isnull
, then no additional restriction is applied.- Returns:
- the value returned by the action's
run
method. - Throws:
NullPointerException
- if the action isnull
- See Also:
-
doPrivileged
public static <T> T doPrivileged(PrivilegedAction<T> action, AccessControlContext context, Permission... perms) Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedAction
with privileges enabled and restricted by the specifiedAccessControlContext
and with a privilege scope limited by specifiedPermission
arguments. The action is performed with the intersection of the permissions possessed by the caller's protection domain, and those possessed by the domains represented by the specifiedAccessControlContext
.If the action's
run
method throws an (unchecked) exception, it will propagate through this method.If a security manager is installed and the specified
AccessControlContext
was not created by system code and the caller'sProtectionDomain
has not been granted the "createAccessControlContext"SecurityPermission
, then the action is performed with no permissions.- Type Parameters:
T
- the type of the value returned by the PrivilegedAction'srun
method.- Parameters:
action
- the action to be performed.context
- an access control context representing the restriction to be applied to the caller's domain's privileges before performing the specified action. If the context isnull
, then no additional restriction is applied.perms
- thePermission
arguments which limit the scope of the caller's privileges. The number of arguments is variable.- Returns:
- the value returned by the action's
run
method. - Throws:
NullPointerException
- if action or perms or any element of perms isnull
- Since:
- 1.8
- See Also:
-
doPrivilegedWithCombiner
public static <T> T doPrivilegedWithCombiner(PrivilegedAction<T> action, AccessControlContext context, Permission... perms) Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedAction
with privileges enabled and restricted by the specifiedAccessControlContext
and with a privilege scope limited by specifiedPermission
arguments. The action is performed with the intersection of the permissions possessed by the caller's protection domain, and those possessed by the domains represented by the specifiedAccessControlContext
.If the action's
run
method throws an (unchecked) exception, it will propagate through this method.This method preserves the current AccessControlContext's
DomainCombiner
(which may be null) while the action is performed.If a security manager is installed and the specified
AccessControlContext
was not created by system code and the caller'sProtectionDomain
has not been granted the "createAccessControlContext"SecurityPermission
, then the action is performed with no permissions.- Type Parameters:
T
- the type of the value returned by the PrivilegedAction'srun
method.- Parameters:
action
- the action to be performed.context
- an access control context representing the restriction to be applied to the caller's domain's privileges before performing the specified action. If the context isnull
, then no additional restriction is applied.perms
- thePermission
arguments which limit the scope of the caller's privileges. The number of arguments is variable.- Returns:
- the value returned by the action's
run
method. - Throws:
NullPointerException
- if action or perms or any element of perms isnull
- Since:
- 1.8
- See Also:
-
doPrivileged
public static <T> T doPrivileged(PrivilegedExceptionAction<T> action) throws PrivilegedActionException Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedExceptionAction
with privileges enabled. The action is performed with all of the permissions possessed by the caller's protection domain.If the action's
run
method throws an unchecked exception, it will propagate through this method.Note that any
DomainCombiner
associated with the currentAccessControlContext
will be ignored while the action is performed.- Type Parameters:
T
- the type of the value returned by the PrivilegedExceptionAction'srun
method.- Parameters:
action
- the action to be performed- Returns:
- the value returned by the action's
run
method - Throws:
PrivilegedActionException
- if the specified action'srun
method threw a checked exceptionNullPointerException
- if the action isnull
- See Also:
-
doPrivilegedWithCombiner
public static <T> T doPrivilegedWithCombiner(PrivilegedExceptionAction<T> action) throws PrivilegedActionException Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedExceptionAction
with privileges enabled. The action is performed with all of the permissions possessed by the caller's protection domain.If the action's
run
method throws an unchecked exception, it will propagate through this method.This method preserves the current AccessControlContext's
DomainCombiner
(which may be null) while the action is performed.- Type Parameters:
T
- the type of the value returned by the PrivilegedExceptionAction'srun
method.- Parameters:
action
- the action to be performed.- Returns:
- the value returned by the action's
run
method - Throws:
PrivilegedActionException
- if the specified action'srun
method threw a checked exceptionNullPointerException
- if the action isnull
- Since:
- 1.6
- See Also:
-
doPrivileged
public static <T> T doPrivileged(PrivilegedExceptionAction<T> action, AccessControlContext context) throws PrivilegedActionException Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedExceptionAction
with privileges enabled and restricted by the specifiedAccessControlContext
. The action is performed with the intersection of the permissions possessed by the caller's protection domain, and those possessed by the domains represented by the specifiedAccessControlContext
.If the action's
run
method throws an unchecked exception, it will propagate through this method.If a security manager is installed and the specified
AccessControlContext
was not created by system code and the caller'sProtectionDomain
has not been granted the "createAccessControlContext"SecurityPermission
, then the action is performed with no permissions.- Type Parameters:
T
- the type of the value returned by the PrivilegedExceptionAction'srun
method.- Parameters:
action
- the action to be performedcontext
- an access control context representing the restriction to be applied to the caller's domain's privileges before performing the specified action. If the context isnull
, then no additional restriction is applied.- Returns:
- the value returned by the action's
run
method - Throws:
PrivilegedActionException
- if the specified action'srun
method threw a checked exceptionNullPointerException
- if the action isnull
- See Also:
-
doPrivileged
public static <T> T doPrivileged(PrivilegedExceptionAction<T> action, AccessControlContext context, Permission... perms) throws PrivilegedActionException Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedExceptionAction
with privileges enabled and restricted by the specifiedAccessControlContext
and with a privilege scope limited by specifiedPermission
arguments. The action is performed with the intersection of the permissions possessed by the caller's protection domain, and those possessed by the domains represented by the specifiedAccessControlContext
.If the action's
run
method throws an (unchecked) exception, it will propagate through this method.If a security manager is installed and the specified
AccessControlContext
was not created by system code and the caller'sProtectionDomain
has not been granted the "createAccessControlContext"SecurityPermission
, then the action is performed with no permissions.- Type Parameters:
T
- the type of the value returned by the PrivilegedExceptionAction'srun
method.- Parameters:
action
- the action to be performed.context
- an access control context representing the restriction to be applied to the caller's domain's privileges before performing the specified action. If the context isnull
, then no additional restriction is applied.perms
- thePermission
arguments which limit the scope of the caller's privileges. The number of arguments is variable.- Returns:
- the value returned by the action's
run
method. - Throws:
PrivilegedActionException
- if the specified action'srun
method threw a checked exceptionNullPointerException
- if action or perms or any element of perms isnull
- Since:
- 1.8
- See Also:
-
doPrivilegedWithCombiner
public static <T> T doPrivilegedWithCombiner(PrivilegedExceptionAction<T> action, AccessControlContext context, Permission... perms) throws PrivilegedActionException Deprecated, for removal: This API element is subject to removal in a future version.Performs the specifiedPrivilegedExceptionAction
with privileges enabled and restricted by the specifiedAccessControlContext
and with a privilege scope limited by specifiedPermission
arguments. The action is performed with the intersection of the permissions possessed by the caller's protection domain, and those possessed by the domains represented by the specifiedAccessControlContext
.If the action's
run
method throws an (unchecked) exception, it will propagate through this method.This method preserves the current AccessControlContext's
DomainCombiner
(which may be null) while the action is performed.If a security manager is installed and the specified
AccessControlContext
was not created by system code and the caller'sProtectionDomain
has not been granted the "createAccessControlContext"SecurityPermission
, then the action is performed with no permissions.- Type Parameters:
T
- the type of the value returned by the PrivilegedExceptionAction'srun
method.- Parameters:
action
- the action to be performed.context
- an access control context representing the restriction to be applied to the caller's domain's privileges before performing the specified action. If the context isnull
, then no additional restriction is applied.perms
- thePermission
arguments which limit the scope of the caller's privileges. The number of arguments is variable.- Returns:
- the value returned by the action's
run
method. - Throws:
PrivilegedActionException
- if the specified action'srun
method threw a checked exceptionNullPointerException
- if action or perms or any element of perms isnull
- Since:
- 1.8
- See Also:
-
getContext
Deprecated, for removal: This API element is subject to removal in a future version.This method takes a "snapshot" of the current calling context, which includes the current thread's inheritedAccessControlContext
and any limited privilege scope, and places it in anAccessControlContext
object. This context may then be checked at a later point, possibly in another thread.- Returns:
- the
AccessControlContext
based on the current context. - See Also:
-
checkPermission
Deprecated, for removal: This API element is subject to removal in a future version.Determines whether the access request indicated by the specified permission should be allowed or denied, based on the currentAccessControlContext
and security policy. This method quietly returns if the access request is permitted, or throws anAccessControlException
otherwise. ThegetPermission
method of theAccessControlException
returns thePermission
object instance (perm
}.- Parameters:
perm
- the requested permission.- Throws:
AccessControlException
- if the specified permission is not permitted, based on the current security policy.NullPointerException
- if the specified permission isnull
and is checked based on the security policy currently in effect.
-