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jeremybenn |
/* NotificationBroadcasterSupport.java -- Supporting implementation.
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Copyright (C) 2007 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package javax.management;
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import gnu.javax.management.ListenerData;
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import java.util.ArrayList;
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import java.util.Iterator;
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import java.util.List;
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import java.util.concurrent.Executor;
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/**
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* <p>
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* Provides an implementation of the {@link NotificationEmitter}
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* interface, which beans may utilise by extension. By default,
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* a synchronous dispatch system is provided, whereby the
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* {@link #handleNotification(NotificationListener, Notification,
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* Object)} is called once per listener by
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* {*@link #sendNotification(Notification)} before returning.
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* Thus, unless the listener is remote, it will have received
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* the notification before the method returns.
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* This may be changed by overriding the <code>handleNotification</code>
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* method, or by providing an {@link java.util.concurrent.Executor} to
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* use. With the latter, the dispatch of a notification to a particular
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* listener will form one task performed by the executor.
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* </p>
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* <p>
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* Any exceptions thrown by the dispatch process will be caught, allowing
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* other listeners to still receive the notification. However, any
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* {@link Error}s that are thrown will be propogated to the caller of
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* {@link #sendNotification(Notification)}.
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* </p>
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*
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* @author Andrew John Hughes (gnu_andrew@member.fsf.org)
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* @since 1.5
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*/
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public class NotificationBroadcasterSupport
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implements NotificationEmitter
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{
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/**
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* The executor for dispatch, or
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* <code>null</code> if this thread should
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* handle dispatch itself.
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*/
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private Executor executor;
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/**
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* An array containing information on each
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* notification, or <code>null</code> if an
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* empty array should be returned by
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* {@link #getNotificationInfo()}.
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*/
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private MBeanNotificationInfo[] info;
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/**
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* The list of listeners registered with
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* this broadcaster.
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*/
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private final List<ListenerData> listeners =
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new ArrayList<ListenerData>();
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/**
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* Constructs a {@link NotificationBroadcasterSupport} using
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* the default synchronous dispatch model, where a single
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* thread sends the notification to all listeners. This
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* is equivalent to calling
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* <code>NotificationBroadcasterSupport(null, null)</code>.
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*/
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public NotificationBroadcasterSupport()
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{
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this(null, (MBeanNotificationInfo[]) null);
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}
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/**
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* Constructs a {@link NotificationBroadcasterSupport} where
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* the specified (@link java.util.concurrent.Executor} is used
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* to perform each invocation of the
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* {@link #handleNotification(NotificationListener, Notification,
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* Object)} method. Filtering is performed beforehand, by this
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* thread; only calls which have successfully passed through the
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* filter are sent to the executor. This is equivalent to calling
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* <code>NotificationBroadcasterSupport(executor, null)</code>.
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*
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* @param executor the executor to use for each call to
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* <code>handleNotification()</code>.
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* @since 1.6
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*/
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public NotificationBroadcasterSupport(Executor executor)
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{
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this(executor, (MBeanNotificationInfo) null);
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}
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/**
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* Constructs a {@link NotificationBroadcasterSupport} using
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* the default synchronous dispatch model, where a single
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* thread sends the notification to all listeners. The specified
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* {@link MBeanNotificationInfo} array is used to provide
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* information about the notifications on calls to
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* {@link #getNotificationInfo()}, where a clone will be
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* returned if the array is non-empty. This is equivalent to
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* calling <code>NotificationBroadcasterSupport(null, info)</code>.
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*
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* @param info an array of {@link MBeanNotificationInfo} objects
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* describing the notifications delivered by this
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* broadcaster. This may be <code>null</code>, which
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* is taken as being equivalent to an empty array.
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*/
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public NotificationBroadcasterSupport(MBeanNotificationInfo... info)
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{
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this(null, info);
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}
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/**
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* Constructs a {@link NotificationBroadcasterSupport} where
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* the specified (@link java.util.concurrent.Executor} is used
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* to perform each invocation of the
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* {@link #handleNotification(NotificationListener, Notification,
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* Object)} method. Filtering is performed beforehand, by this
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* thread; only calls which have successfully passed through the
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* filter are sent to the executor. The specified
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* {@link MBeanNotificationInfo} array is used to provide
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* information about the notifications on calls to
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* {@link #getNotificationInfo()}, where a clone will be
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* returned if the array is non-empty.
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*
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* @param executor the executor to use for each call to
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* <code>handleNotification()</code>.
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* @param info an array of {@link MBeanNotificationInfo} objects
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* describing the notifications delivered by this
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* broadcaster. This may be <code>null</code>, which
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* is taken as being equivalent to an empty array.
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* @since 1.6
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*/
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public NotificationBroadcasterSupport(Executor executor,
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MBeanNotificationInfo... info)
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{
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this.executor = executor;
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this.info = info;
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}
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/**
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* Registers the specified listener as a new recipient of
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* notifications from this bean. If non-null, the filter
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* argument will be used to select which notifications are
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* delivered. The supplied object will also be passed to
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* the recipient with each notification. This should not
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* be modified by the broadcaster, but instead should be
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* passed unmodified to the listener.
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*
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* @param listener the new listener, who will receive
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* notifications from this broadcasting bean.
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* @param filter a filter to determine which notifications are
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* delivered to the listener, or <code>null</code>
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* if no filtering is required.
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* @param passback an object to be passed to the listener with
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* each notification.
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* @throws IllegalArgumentException if <code>listener</code> is
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* <code>null</code>.
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* @see #removeNotificationListener(NotificationListener)
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*/
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public void addNotificationListener(NotificationListener listener,
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NotificationFilter filter,
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Object passback)
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throws IllegalArgumentException
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{
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if (listener == null)
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throw new IllegalArgumentException("Null listener added to bean.");
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listeners.add(new ListenerData(listener, filter, passback));
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}
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/**
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* Returns an array describing the notifications this
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* bean may send to its registered listeners. Ideally, this
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* array should be complete, but in some cases, this may
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* not be possible. However, be aware that some listeners
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* may expect this to be so.
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*
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* @return the array of possible notifications.
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*/
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public MBeanNotificationInfo[] getNotificationInfo()
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{
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if (info == null || info.length == 0)
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return new MBeanNotificationInfo[0];
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return (MBeanNotificationInfo[]) info.clone();
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}
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/**
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* This method is called on a per-listener basis, either
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* from this thread or the supplied executor, and may be
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* overridden by subclasses which wish to change how
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* notifications are delivered. The default
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* implementation simply calls
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* <code>listener.handleNotification(notif, passback)</code>.
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*
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* @param listener the listener to send the notification to.
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* @param notif the notification to dispatch.
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* @param passback the passback object of the listener.
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*/
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protected void handleNotification(NotificationListener listener,
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Notification notif,
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Object passback)
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{
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listener.handleNotification(notif, passback);
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}
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/**
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* Removes the specified listener from the list of recipients
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* of notifications from this bean. This includes all combinations
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* of filters and passback objects registered for this listener.
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* For more specific removal of listeners, see the subinterface
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* {@link NotificationEmitter}.
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*
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* @param listener the listener to remove.
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* @throws ListenerNotFoundException if the specified listener
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* is not registered with this bean.
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* @see #addNotificationListener(NotificationListener, NotificationFilter,
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* java.lang.Object)
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*/
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public void removeNotificationListener(NotificationListener listener)
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throws ListenerNotFoundException
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{
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Iterator<ListenerData> it = listeners.iterator();
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boolean foundOne = false;
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while (it.hasNext())
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{
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if (it.next().getListener() == listener)
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{
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it.remove();
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foundOne = true;
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}
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}
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if (!foundOne)
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throw new ListenerNotFoundException("The specified listener, " + listener +
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"is not registered with this bean.");
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}
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/**
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* Removes the specified listener from the list of recipients
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* of notifications from this bean. Only the first instance with
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* the supplied filter and passback object is removed.
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* <code>null</code> is used as a valid value for these parameters,
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* rather than as a way to remove all registration instances for
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* the specified listener; for this behaviour instead, see the details
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* of the same method in {@link NotificationBroadcaster}.
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*
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* @param listener the listener to remove.
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* @param filter the filter of the listener to remove.
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* @param passback the passback object of the listener to remove.
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* @throws ListenerNotFoundException if the specified listener
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* is not registered with this bean.
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* @see #addNotificationListener(NotificationListener, NotificationFilter,
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* java.lang.Object)
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*/
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public void removeNotificationListener(NotificationListener listener,
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NotificationFilter filter,
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Object passback)
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throws ListenerNotFoundException
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{
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if (!(listeners.remove(new ListenerData(listener, filter, passback))))
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{
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throw new ListenerNotFoundException("The specified listener, " + listener +
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" with filter " + filter +
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"and passback " + passback +
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", is not registered with this bean.");
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}
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}
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/**
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* <p>
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* Performs delivery of the notification. If an executor
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* was specified on construction, this will be used to call
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* {@link #handleNotification(NotificationListener, Notification,
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* Object)}. If the executor is <code>null</code>, however,
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* this thread calls the method itself in order to perform a
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* synchronous dispatch of the notification to all eligible
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* listeners.
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* </p>
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* <p>
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* Prior to either process taking place, the listeners are filtered.
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* Notifications are only delivered if the filter is either
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* <code>null</code> or returns true from the
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* {@link NotificationFilter#isNotificationEnabled(Notification)}
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* method.
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* </p>
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*
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* @param notif the notification to send.
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*/
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public void sendNotification(Notification notif)
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{
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for (ListenerData ldata : listeners)
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{
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NotificationFilter filter = ldata.getFilter();
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if (filter == null || filter.isNotificationEnabled(notif))
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{
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if (executor == null)
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try
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{
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handleNotification(ldata.getListener(), notif,
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ldata.getPassback());
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}
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catch (Exception e) { /* Ignore */ }
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else
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executor.execute(new DispatchTask(ldata, notif));
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}
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}
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}
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/**
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* The dispatch task to be performed by an executor.
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*/
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private final class DispatchTask
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implements Runnable
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{
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|
|
/**
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* The data on the listener being called.
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*/
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private ListenerData ldata;
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/**
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* The notification to send.
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*/
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private Notification notif;
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/**
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* Construct a new {@link DispatchTask}.
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*
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* @param ldata the listener data.
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* @param notif the notification to send.
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*/
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368 |
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public DispatchTask(ListenerData ldata,
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|
Notification notif)
|
370 |
|
|
{
|
371 |
|
|
this.ldata = ldata;
|
372 |
|
|
this.notif = notif;
|
373 |
|
|
}
|
374 |
|
|
|
375 |
|
|
/**
|
376 |
|
|
* Dispatch the notification.
|
377 |
|
|
*/
|
378 |
|
|
public void run()
|
379 |
|
|
{
|
380 |
|
|
try
|
381 |
|
|
{
|
382 |
|
|
handleNotification(ldata.getListener(), notif,
|
383 |
|
|
ldata.getPassback());
|
384 |
|
|
}
|
385 |
|
|
catch (Exception e) { /* Ignore */ }
|
386 |
|
|
}
|
387 |
|
|
}
|
388 |
|
|
|
389 |
|
|
}
|