Context
EventDirContext
public interface EventContext extends Context
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.
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:
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 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.
removeNamingListener()
. NamingExceptionEvent
. Context.close()
is invoked on the EventContext
instance with which it has registered. EventContext
instance that has outstanding listeners will continue to exist and be maintained by the service provider. 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. 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.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. |
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
Modifier and Type | Method | Description |
---|---|---|
void |
addNamingListener |
Adds a listener for receiving naming events fired when the object named by the string target name and scope changes. |
void |
addNamingListener |
Adds a listener for receiving naming events fired when the object(s) identified by a target and scope changes. |
void |
removeNamingListener |
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. |
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
static final int OBJECT_SCOPE
The value of this constant is 0
.
static final int ONELEVEL_SCOPE
The value of this constant is 1
.
static final int SUBTREE_SCOPE
The value of this constant is 2
.
void addNamingListener(Name target, int scope, NamingListener l) throws NamingException
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.
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.NamingException
- If a problem was encountered while adding the listener.void addNamingListener(String target, int scope, NamingListener l) throws NamingException
Name
for details.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.NamingException
- If a problem was encountered while adding the listener.void removeNamingListener(NamingListener l) throws NamingException
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.l
- The nonnull listener.NamingException
- If a problem was encountered while removing the listener.boolean targetMustExist() throws NamingException
NamingException
- If the context's behavior in this regard cannot be determined.
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/21/docs/api/java.naming/javax/naming/event/EventContext.html