Interface EventContext

All Superinterfaces:

Context

All Known Subinterfaces:

EventDirContext

public interface EventContext
extends Context

Contains methods for registering/deregistering listeners to be notified of events fired when objects named in a context changes.

Target

The name parameter in the addNamingListener() methods is referred to as the target. The target, along with the scope, identify the object(s) that the listener is interested in. It is possible to register interest in a target that does not exist, but there might be limitations in the extent to which this can be supported by the service provider and underlying protocol/service.

If a service only supports registration for existing targets, an attempt to register for a nonexistent target results in a NameNotFoundException being thrown as early as possible, preferably at the time addNamingListener() is called, or if that is not possible, the listener will receive the exception through the NamingExceptionEvent.

Also, for service providers that only support registration for existing targets, when the target that a listener has registered for is subsequently removed from the namespace, the listener is notified via a NamingExceptionEvent (containing a NameNotFoundException).

An application can use the method targetMustExist() to check whether an EventContext supports registration of nonexistent targets.

Event Source

The EventContext instance on which you invoke the registration methods is the event source of the events that are (potentially) generated. The source is not necessarily the object named by the target. Only when the target is the empty name is the object named by the target the source. In other words, the target, along with the scope parameter, are used to identify the object(s) that the listener is interested in, but the event source is the EventContext instance with which the listener has registered.

For example, suppose a listener makes the following registration:

      NamespaceChangeListener listener = ...;
      src.addNamingListener("x", SUBTREE_SCOPE, listener);

When an object named "x/y" is subsequently deleted, the corresponding NamingEvent (evt) must contain:

      evt.getEventContext() == src
      evt.getOldBinding().getName().equals("x/y")

Furthermore, listener registration/deregistration is with the EventContext instance, and not with the corresponding object in the namespace. If the program intends at some point to remove a listener, then it needs to keep a reference to the EventContext instance on which it invoked addNamingListener() (just as it needs to keep a reference to the listener in order to remove it later). It cannot expect to do a lookup() and get another instance of an EventContext on which to perform the deregistration.

Lifetime of Registration

A registered listener becomes deregistered when:

• It is removed using removeNamingListener().
• An exception is thrown while collecting information about the events. That is, when the listener receives a NamingExceptionEvent.
• Context.close() is invoked on the EventContext instance with which it has registered.

Until that point, an EventContext instance that has outstanding listeners will continue to exist and be maintained by the service provider.

Listener Implementations

The registration/deregistration methods accept an instance of NamingListener. There are subinterfaces of NamingListener for different of event types of NamingEvent. For example, the ObjectChangeListener interface is for the NamingEvent.OBJECT_CHANGED event type. To register interest in multiple event types, the listener implementation should implement multiple NamingListener subinterfaces and use a single invocation of addNamingListener(). In addition to reducing the number of method calls and possibly the code size of the listeners, this allows some service providers to optimize the registration.

Threading Issues

Like Context instances in general, instances of EventContext are not guaranteed to be thread-safe. Care must be taken when multiple threads are accessing the same EventContext concurrently. See the package description for more information on threading issues.

Since:

1.3

Field Summary

Fields

Modifier and Type	Field	Description
static final int	OBJECT_SCOPE	Constant for expressing interest in events concerning the object named by the target.
static final int	ONELEVEL_SCOPE	Constant for expressing interest in events concerning objects in the context named by the target, excluding the context named by the target.
static final int	SUBTREE_SCOPE	Constant for expressing interest in events concerning objects in the subtree of the object named by the target, including the object named by the target.

Fields declared in interface Context

AUTHORITATIVE, BATCHSIZE, DNS_URL, INITIAL_CONTEXT_FACTORY, LANGUAGE, OBJECT_FACTORIES, PROVIDER_URL, REFERRAL, SECURITY_AUTHENTICATION, SECURITY_CREDENTIALS, SECURITY_PRINCIPAL, SECURITY_PROTOCOL, STATE_FACTORIES, URL_PKG_PREFIXES

Modifier and Type	Field	Description
static final String	AUTHORITATIVE	Constant that holds the name of the environment property for specifying the authoritativeness of the service requested.
static final String	BATCHSIZE	Constant that holds the name of the environment property for specifying the batch size to use when returning data via the service's protocol.
static final String	DNS_URL	Constant that holds the name of the environment property for specifying the DNS host and domain names to use for the JNDI URL context (for example, "dns://somehost/wiz.com").
static final String	INITIAL_CONTEXT_FACTORY	Constant that holds the name of the environment property for specifying the initial context factory to use.
static final String	LANGUAGE	Constant that holds the name of the environment property for specifying the preferred language to use with the service.
static final String	OBJECT_FACTORIES	Constant that holds the name of the environment property for specifying the list of object factories to use.
static final String	PROVIDER_URL	Constant that holds the name of the environment property for specifying configuration information for the service provider to use.
static final String	REFERRAL	Constant that holds the name of the environment property for specifying how referrals encountered by the service provider are to be processed.
static final String	SECURITY_AUTHENTICATION	Constant that holds the name of the environment property for specifying the security level to use.
static final String	SECURITY_CREDENTIALS	Constant that holds the name of the environment property for specifying the credentials of the principal for authenticating the caller to the service.
static final String	SECURITY_PRINCIPAL	Constant that holds the name of the environment property for specifying the identity of the principal for authenticating the caller to the service.
static final String	SECURITY_PROTOCOL	Constant that holds the name of the environment property for specifying the security protocol to use.
static final String	STATE_FACTORIES	Constant that holds the name of the environment property for specifying the list of state factories to use.
static final String	URL_PKG_PREFIXES	Constant that holds the name of the environment property for specifying the list of package prefixes to use when loading in URL context factories.

Method Summary

Modifier and Type	Method	Description
void	addNamingListener(String target, int scope, NamingListener l)	Adds a listener for receiving naming events fired when the object named by the string target name and scope changes.
void	addNamingListener(Name target, int scope, NamingListener l)	Adds a listener for receiving naming events fired when the object(s) identified by a target and scope changes.
void	removeNamingListener(NamingListener l)	Removes a listener from receiving naming events fired by this EventContext.
boolean	targetMustExist()	Determines whether a listener can register interest in a target that does not exist.

Methods declared in interface Context

addToEnvironment, bind, bind, close, composeName, composeName, createSubcontext, createSubcontext, destroySubcontext, destroySubcontext, getEnvironment, getNameInNamespace, getNameParser, getNameParser, list, list, listBindings, listBindings, lookup, lookup, lookupLink, lookupLink, rebind, rebind, removeFromEnvironment, rename, rename, unbind, unbind

Modifier and Type	Method	Description
Object	addToEnvironment(String propName, Object propVal)	Adds a new environment property to the environment of this context.
void	bind(String name, Object obj)	Binds a name to an object.
void	bind(Name name, Object obj)	Binds a name to an object.
void	close()	Closes this context.
String	composeName(String name, String prefix)	Composes the name of this context with a name relative to this context.
Name	composeName(Name name, Name prefix)	Composes the name of this context with a name relative to this context.
Context	createSubcontext(String name)	Creates and binds a new context.
Context	createSubcontext(Name name)	Creates and binds a new context.
void	destroySubcontext(String name)	Destroys the named context and removes it from the namespace.
void	destroySubcontext(Name name)	Destroys the named context and removes it from the namespace.
Hashtable<?,?>	getEnvironment()	Retrieves the environment in effect for this context.
String	getNameInNamespace()	Retrieves the full name of this context within its own namespace.
NameParser	getNameParser(String name)	Retrieves the parser associated with the named context.
NameParser	getNameParser(Name name)	Retrieves the parser associated with the named context.
NamingEnumeration<NameClassPair>	list(String name)	Enumerates the names bound in the named context, along with the class names of objects bound to them.
NamingEnumeration<NameClassPair>	list(Name name)	Enumerates the names bound in the named context, along with the class names of objects bound to them.
NamingEnumeration<Binding>	listBindings(String name)	Enumerates the names bound in the named context, along with the objects bound to them.
NamingEnumeration<Binding>	listBindings(Name name)	Enumerates the names bound in the named context, along with the objects bound to them.
Object	lookup(String name)	Retrieves the named object.
Object	lookup(Name name)	Retrieves the named object.
Object	lookupLink(String name)	Retrieves the named object, following links except for the terminal atomic component of the name.
Object	lookupLink(Name name)	Retrieves the named object, following links except for the terminal atomic component of the name.
void	rebind(String name, Object obj)	Binds a name to an object, overwriting any existing binding.
void	rebind(Name name, Object obj)	Binds a name to an object, overwriting any existing binding.
Object	removeFromEnvironment(String propName)	Removes an environment property from the environment of this context.
void	rename(String oldName, String newName)	Binds a new name to the object bound to an old name, and unbinds the old name.
void	rename(Name oldName, Name newName)	Binds a new name to the object bound to an old name, and unbinds the old name.
void	unbind(String name)	Unbinds the named object.
void	unbind(Name name)	Unbinds the named object.

Field Details

OBJECT_SCOPE

static final int OBJECT_SCOPE

Constant for expressing interest in events concerning the object named by the target.

The value of this constant is 0.

See Also:

• Constant Field Values

ONELEVEL_SCOPE

static final int ONELEVEL_SCOPE

Constant for expressing interest in events concerning objects in the context named by the target, excluding the context named by the target.

The value of this constant is 1.

See Also:

• Constant Field Values

SUBTREE_SCOPE

static final int SUBTREE_SCOPE

Constant for expressing interest in events concerning objects in the subtree of the object named by the target, including the object named by the target.

The value of this constant is 2.

See Also:

• Constant Field Values

Method Details

addNamingListener

void addNamingListener(Name target,
 int scope,
 NamingListener l)
                throws NamingException

Adds a listener for receiving naming events fired when the object(s) identified by a target and scope changes. The event source of those events is this context. See the class description for a discussion on event source and target. See the descriptions of the constants OBJECT_SCOPE, ONELEVEL_SCOPE, and SUBTREE_SCOPE to see how scope affects the registration.

target needs to name a context only when scope is ONELEVEL_SCOPE. target may name a non-context if scope is either OBJECT_SCOPE or SUBTREE_SCOPE. Using SUBTREE_SCOPE for a non-context might be useful, for example, if the caller does not know in advance whether target is a context and just wants to register interest in the (possibly degenerate subtree) rooted at target.

When the listener is notified of an event, the listener may in invoked in a thread other than the one in which addNamingListener() is executed. Care must be taken when multiple threads are accessing the same EventContext concurrently. See the package description for more information on threading issues.

Parameters:

target - A nonnull name to be resolved relative to this context.

scope - One of OBJECT_SCOPE, ONELEVEL_SCOPE, or SUBTREE_SCOPE.

l - The nonnull listener.

Throws:

NamingException - If a problem was encountered while adding the listener.

See Also:

• removeNamingListener(NamingListener)

addNamingListener

void addNamingListener(String target,
 int scope,
 NamingListener l)
                throws NamingException

Adds a listener for receiving naming events fired when the object named by the string target name and scope changes. See the overload that accepts a Name for details.

Parameters:

target - The nonnull string name of the object resolved relative to this context.

scope - One of OBJECT_SCOPE, ONELEVEL_SCOPE, or SUBTREE_SCOPE.

l - The nonnull listener.

Throws:

NamingException - If a problem was encountered while adding the listener.

See Also:

• removeNamingListener(NamingListener)

removeNamingListener

void removeNamingListener(NamingListener l)
                   throws NamingException

Removes a listener from receiving naming events fired by this EventContext. The listener may have registered more than once with this EventContext, perhaps with different target/scope arguments. After this method is invoked, the listener will no longer receive events with this EventContext instance as the event source (except for those events already in the process of being dispatched). If the listener was not, or is no longer, registered with this EventContext instance, this method does not do anything.

Parameters:

l - The nonnull listener.

Throws:

NamingException - If a problem was encountered while removing the listener.

See Also:

• addNamingListener(Name, int, NamingListener)

targetMustExist

boolean targetMustExist()
                 throws NamingException

Determines whether a listener can register interest in a target that does not exist.

Returns:

true if the target must exist; false if the target need not exist.

Throws:

NamingException - If the context's behavior in this regard cannot be determined.