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- 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 theaddNamingListener()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
NameNotFoundExceptionbeing thrown as early as possible, preferably at the timeaddNamingListener()is called, or if that is not possible, the listener will receive the exception through theNamingExceptionEvent.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 aNameNotFoundException).An application can use the method
targetMustExist()to check whether anEventContextsupports registration of nonexistent targets.Event Source
TheEventContextinstance 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 theEventContextinstance with which the listener has registered.For example, suppose a listener makes the following registration:
When an object named "x/y" is subsequently deleted, the correspondingNamespaceChangeListener listener = ...; src.addNamingListener("x", SUBTREE_SCOPE, listener);NamingEvent(evt) must contain:evt.getEventContext() == src evt.getOldBinding().getName().equals("x/y")Furthermore, listener registration/deregistration is with the
EventContextinstance, 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 theEventContextinstance on which it invokedaddNamingListener()(just as it needs to keep a reference to the listener in order to remove it later). It cannot expect to do alookup()and get another instance of anEventContexton 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 theEventContextinstance with which it has registered.
EventContextinstance that has outstanding listeners will continue to exist and be maintained by the service provider.Listener Implementations
The registration/deregistration methods accept an instance ofNamingListener. There are subinterfaces ofNamingListenerfor different of event types ofNamingEvent. For example, theObjectChangeListenerinterface is for theNamingEvent.OBJECT_CHANGEDevent type. To register interest in multiple event types, the listener implementation should implement multipleNamingListenersubinterfaces and use a single invocation ofaddNamingListener(). 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
LikeContextinstances in general, instances ofEventContextare not guaranteed to be thread-safe. Care must be taken when multiple threads are accessing the sameEventContextconcurrently. See the package description for more information on threading issues.- Since:
- 1.3
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Field Summary
Fields Modifier and Type Field Description static intOBJECT_SCOPEConstant for expressing interest in events concerning the object named by the target.static intONELEVEL_SCOPEConstant for expressing interest in events concerning objects in the context named by the target, excluding the context named by the target.static intSUBTREE_SCOPEConstant 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 javax.naming.Context
APPLET, 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
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description voidaddNamingListener(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.voidaddNamingListener(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.voidremoveNamingListener(NamingListener l)Removes a listener from receiving naming events fired by thisEventContext.booleantargetMustExist()Determines whether a listener can register interest in a target that does not exist.-
Methods declared in interface javax.naming.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
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Field Detail
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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
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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
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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
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Method Detail
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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 constantsOBJECT_SCOPE,ONELEVEL_SCOPE, andSUBTREE_SCOPEto see howscopeaffects the registration.targetneeds to name a context only whenscopeisONELEVEL_SCOPE.targetmay name a non-context ifscopeis eitherOBJECT_SCOPEorSUBTREE_SCOPE. UsingSUBTREE_SCOPEfor a non-context might be useful, for example, if the caller does not know in advance whethertargetis a context and just wants to register interest in the (possibly degenerate subtree) rooted attarget.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 sameEventContextconcurrently. See the package description for more information on threading issues.- Parameters:
target- A nonnull name to be resolved relative to this context.scope- One ofOBJECT_SCOPE,ONELEVEL_SCOPE, orSUBTREE_SCOPE.l- The nonnull listener.- Throws:
NamingException- If a problem was encountered while adding the listener.- See Also:
removeNamingListener(javax.naming.event.NamingListener)
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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 aNamefor details.- Parameters:
target- The nonnull string name of the object resolved relative to this context.scope- One ofOBJECT_SCOPE,ONELEVEL_SCOPE, orSUBTREE_SCOPE.l- The nonnull listener.- Throws:
NamingException- If a problem was encountered while adding the listener.- See Also:
removeNamingListener(javax.naming.event.NamingListener)
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removeNamingListener
void removeNamingListener(NamingListener l) throws NamingException
Removes a listener from receiving naming events fired by thisEventContext. The listener may have registered more than once with thisEventContext, perhaps with different target/scope arguments. After this method is invoked, the listener will no longer receive events with thisEventContextinstance 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 thisEventContextinstance, 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(javax.naming.Name, int, javax.naming.event.NamingListener)
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targetMustExist
boolean targetMustExist() throws NamingExceptionDetermines 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.
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