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package javax.naming.event;
import javax.naming.Name;
import javax.naming.Context;
import javax.naming.NamingException;
/**
* Contains methods for registering/deregistering listeners to be notified of
* events fired when objects named in a context changes.
*
*<h1>Target</h1>
* The name parameter in the {@code addNamingListener()} methods is referred
* to as the <em>target</em>. 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.
*<p>
* If a service only supports registration for existing
* targets, an attempt to register for a nonexistent target
* results in a {@code NameNotFoundException} being thrown as early as possible,
* preferably at the time {@code addNamingListener()} is called, or if that is
* not possible, the listener will receive the exception through the
* {@code NamingExceptionEvent}.
*<p>
* 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 {@code NamingExceptionEvent} (containing a
*{@code NameNotFoundException}).
*<p>
* An application can use the method {@code targetMustExist()} to check
* whether an {@code EventContext} supports registration
* of nonexistent targets.
*
*<h1>Event Source</h1>
* The {@code EventContext} instance on which you invoke the
* registration methods is the <em>event source</em> of the events that are
* (potentially) generated.
* The source is <em>not necessarily</em> 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 {@code EventContext} instance with which the listener
* has registered.
*<p>
* For example, suppose a listener makes the following registration:
*<blockquote><pre>
* NamespaceChangeListener listener = ...;
* src.addNamingListener("x", SUBTREE_SCOPE, listener);
*</pre></blockquote>
* When an object named "x/y" is subsequently deleted, the corresponding
* {@code NamingEvent} ({@code evt}) must contain:
*<blockquote><pre>
* evt.getEventContext() == src
* evt.getOldBinding().getName().equals("x/y")
*</pre></blockquote>
*<p>
* Furthermore, listener registration/deregistration is with
* the {@code EventContext}
* <em>instance</em>, 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 {@code EventContext} instance on
* which it invoked {@code addNamingListener()} (just as
* it needs to keep a reference to the listener in order to remove it
* later). It cannot expect to do a {@code lookup()} and get another instance of
* an {@code EventContext} on which to perform the deregistration.
*<h1>Lifetime of Registration</h1>
* A registered listener becomes deregistered when:
*<ul>
*<li>It is removed using {@code removeNamingListener()}.
*<li>An exception is thrown while collecting information about the events.
* That is, when the listener receives a {@code NamingExceptionEvent}.
*<li>{@code Context.close()} is invoked on the {@code EventContext}
* instance with which it has registered.
</ul>
* Until that point, an {@code EventContext} instance that has outstanding
* listeners will continue to exist and be maintained by the service provider.
*
*<h1>Listener Implementations</h1>
* The registration/deregistration methods accept an instance of
* {@code NamingListener}. There are subinterfaces of {@code NamingListener}
* for different of event types of {@code NamingEvent}.
* For example, the {@code ObjectChangeListener}
* interface is for the {@code NamingEvent.OBJECT_CHANGED} event type.
* To register interest in multiple event types, the listener implementation
* should implement multiple {@code NamingListener} subinterfaces and use a
* single invocation of {@code 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.
*
*<h1>Threading Issues</h1>
*
* Like {@code Context} instances in general, instances of
* {@code EventContext} are not guaranteed to be thread-safe.
* Care must be taken when multiple threads are accessing the same
* {@code EventContext} concurrently.
* See the
* <a href=package-summary.html#THREADING>package description</a>
* for more information on threading issues.
*
* @author Rosanna Lee
* @author Scott Seligman
* @since 1.3
*/
public interface EventContext extends Context {
/**
* Constant for expressing interest in events concerning the object named
* by the target.
*<p>
* The value of this constant is {@code 0}.
*/
public final static int OBJECT_SCOPE = 0;
/**
* Constant for expressing interest in events concerning objects
* in the context named by the target,
* excluding the context named by the target.
*<p>
* The value of this constant is {@code 1}.
*/
public final static int ONELEVEL_SCOPE = 1;
/**
* 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.
*<p>
* The value of this constant is {@code 2}.
*/
public final static int SUBTREE_SCOPE = 2;
/**
* 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 {@code OBJECT_SCOPE},
* {@code ONELEVEL_SCOPE}, and {@code SUBTREE_SCOPE} to see how
* {@code scope} affects the registration.
*<p>
* {@code target} needs to name a context only when {@code scope} is
* {@code ONELEVEL_SCOPE}.
* {@code target} may name a non-context if {@code scope} is either
* {@code OBJECT_SCOPE} or {@code SUBTREE_SCOPE}. Using
* {@code SUBTREE_SCOPE} for a non-context might be useful,
* for example, if the caller does not know in advance whether {@code target}
* is a context and just wants to register interest in the (possibly
* degenerate subtree) rooted at {@code target}.
*<p>
* When the listener is notified of an event, the listener may
* in invoked in a thread other than the one in which
* {@code addNamingListener()} is executed.
* Care must be taken when multiple threads are accessing the same
* {@code EventContext} concurrently.
* See the
* <a href=package-summary.html#THREADING>package description</a>
* for more information on threading issues.
*
* @param target A nonnull name to be resolved relative to this context.
* @param scope One of {@code OBJECT_SCOPE}, {@code ONELEVEL_SCOPE}, or
* {@code SUBTREE_SCOPE}.
* @param l The nonnull listener.
* @exception NamingException If a problem was encountered while
* adding the listener.
* @see #removeNamingListener
*/
void addNamingListener(Name 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 {@code Name} for details.
*
* @param target The nonnull string name of the object resolved relative
* to this context.
* @param scope One of {@code OBJECT_SCOPE}, {@code ONELEVEL_SCOPE}, or
* {@code SUBTREE_SCOPE}.
* @param l The nonnull listener.
* @exception NamingException If a problem was encountered while
* adding the listener.
* @see #removeNamingListener
*/
void addNamingListener(String target, int scope, NamingListener l)
throws NamingException;
/**
* Removes a listener from receiving naming events fired
* by this {@code EventContext}.
* The listener may have registered more than once with this
* {@code EventContext}, perhaps with different target/scope arguments.
* After this method is invoked, the listener will no longer
* receive events with this {@code 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 {@code EventContext} instance, this method does not do anything.
*
* @param l The nonnull listener.
* @exception NamingException If a problem was encountered while
* removing the listener.
* @see #addNamingListener
*/
void removeNamingListener(NamingListener l) throws NamingException;
/**
* Determines whether a listener can register interest in a target
* that does not exist.
*
* @return true if the target must exist; false if the target need not exist.
* @exception NamingException If the context's behavior in this regard cannot
* be determined.
*/
boolean targetMustExist() throws NamingException;
}