<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!--Copyright (c) 1999, 2006, Oracle and/or its affiliates. All rights reserved.DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. This code is free software; you can redistribute it and/or modify itunder the terms of the GNU General Public License version 2 only, aspublished by the Free Software Foundation.  Oracle designates thisparticular file as subject to the "Classpath" exception as providedby Oracle in the LICENSE file that accompanied this code. This code is distributed in the hope that it will be useful, but WITHOUTANY WARRANTY; without even the implied warranty of MERCHANTABILITY orFITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public Licenseversion 2 for more details (a copy is included in the LICENSE file thataccompanied this code). You should have received a copy of the GNU General Public License version2 along with this work; if not, write to the Free Software Foundation,Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USAor visit www.oracle.com if you need additional information or have anyquestions.--></head><body bgcolor="white"> Provides support for event notification when accessing naming anddirectory services. <p>This package defines the event notification operations of the Java Namingand Directory Interface<font size=-2><sup>TM</sup></font> (JNDI). &nbsp;JNDI provides naming and directory functionality to applicationswritten in the Java programming language.  It is designed to beindependent of any specific naming or directory serviceimplementation.  Thus a variety of services--new, emerging, andalready deployed ones--can be accessed in a common way. <h4>Naming Events</h4><p>This package defines a <tt>NamingEvent</tt> class to represent an eventthat is generated by a naming/directory service.It also defines subinterfaces of <tt>Context</tt> and <tt>DirContext</tt>,called <tt>EventContext</tt> and <tt>EventDirContext</tt>,through which applications can register their interest in eventsfired by the context.<p><tt>NamingEvent</tt> represents an event that occurs in a naming or directory service. There are two categories of naming events:<ul><li>Those that affect the namespace (add/remove/rename an object)<li>Those that affect the objects' contents.</ul>Each category of events is handled by a corresponding listener:<tt>NamespaceChangeListener</tt>, <tt>ObjectChangeListener</tt>.<p>An application, for example, can register its interest in changes toobjects in a context as follows:<blockquote><pre>EventContext src =     (EventContext)(new InitialContext()).lookup("o=wiz,c=us");src.addNamingListener("ou=users", EventContext.ONELEVEL_SCOPE,    new ChangeHandler());...class ChangeHandler implements ObjectChangeListener {    public void objectChanged(NamingEvent evt) {        System.out.println(evt.getNewBinding());    }    public void namingExceptionThrown(NamingExceptionEvent evt) {        System.out.println(evt.getException());    }}</pre></blockquote> <a name=THREADING></a><h4>Threading Issues</h4> When an event is dispatched to a listener, the listener method (suchas <tt>objectChanged()</tt>) may be executed in a thread other than theone in which the call to <tt>addNamingListener()</tt> was executed.The choice of which thread to use is made by the service provider.When an event is dispatched to multiple listeners, the service providermay choose (and is generally encouraged) to execute the listener methodsconcurrently in separate threads.<p>When a listener instance invokes <tt>NamingEvent.getEventContext()</tt>,it must take into account the possibility that other threads will beworking with that context concurrently.  Likewise, when a listener isregistered via <tt>addNamingListener()</tt>, the registering threadmust take into account the likely possibility that the service providerwill later invoke the listeners in newly-created threads.  As <tt>Context</tt>instances are not guaranteed to be thread-safe in general, all contextoperations must be synchronized as needed. <h4>Exception Handling</h4> When a listener registers for events with a context, the context mightneed to do some internal processing in order to collect informationrequired to generate the events.  The context, for example, might needto make a request to the server to register interest in changeson the server that will eventually be translated into events.If an exception occurs that prevents information about the events frombeing collected, the listener will never be notified of the events.When such an exception occurs, a <tt>NamingExceptionEvent</tt> isfired to notify the listener. The listener's<tt>namingExceptionThrown()</tt> method is invoked, as shown in the sample code above,and the listener is automatically deregistered.<p> <h2>Package Specification</h2>  The JNDI API Specification and related documents can be found in the<a href="../../../../technotes/guides/jndi/index.html">JNDI documentation</a>. @since 1.3 </body></html>