- All Superinterfaces:
Context
- All Known Subinterfaces:
EventDirContext
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 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
TheEventContext 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);
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 theEventContextinstance with which it has registered.
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 ofNamingListener. 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
LikeContext 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
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Field Summary
FieldsModifier and TypeFieldDescriptionstatic final intConstant for expressing interest in events concerning the object named by the target.static final intConstant for expressing interest in events concerning objects in the context named by the target, excluding the context named by the target.static final intConstant 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 -
Method Summary
Modifier and TypeMethodDescriptionvoidaddNamingListener(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.voidRemoves a listener from receiving naming events fired by thisEventContext.booleanDetermines 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 Details
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OBJECT_SCOPE
static final int OBJECT_SCOPEConstant for expressing interest in events concerning the object named by the target.The value of this constant is
0.- See Also:
-
ONELEVEL_SCOPE
static final int ONELEVEL_SCOPEConstant 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:
-
SUBTREE_SCOPE
static final int SUBTREE_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.The value of this constant is
2.- See Also:
-
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Method Details
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addNamingListener
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:
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addNamingListener
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:
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removeNamingListener
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:
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targetMustExist
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.
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