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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.

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.

Author:Rosanna Lee, Scott Seligman
Since:1.3
/**
 * 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.

 The value of this constant is 0. 
/**
     * 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.

 The value of this constant is 1. 
/**
     * 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.

 The value of this constant is 2. 
/**
     * 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 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.

Params:
  • 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:
/**
     * 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 Name for details. 
Params:
  • 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:
/**
     * 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 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. 
Params:
  • l –  The nonnull listener.
Throws:
  • NamingException – If a problem was encountered while
removing the listener.
See Also:
/**
     * 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.

Throws:
  • NamingException – If the context's behavior in this regard cannot
be determined.
Returns:true if the target must exist; false if the target need not exist.
/**
     * 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;
}