queueconsumerendpoint.java

一个java方面的消息订阅发送的源码

/**
 * Redistribution and use of this software and associated documentation
 * ("Software"), with or without modification, are permitted provided
 * that the following conditions are met:
 *
 * 1. Redistributions of source code must retain copyright
 *    statements and notices.  Redistributions must also contain a
 *    copy of this document.
 *
 * 2. Redistributions in binary form must reproduce the
 *    above copyright notice, this list of conditions and the
 *    following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. The name "Exolab" must not be used to endorse or promote
 *    products derived from this Software without prior written
 *    permission of Exoffice Technologies.  For written permission,
 *    please contact [e-mail].
 *
 * 4. Products derived from this Software may not be called "Exolab"
 *    nor may "Exolab" appear in their names without prior written
 *    permission of Exoffice Technologies. Exolab is a registered
 *    trademark of Exoffice Technologies.
 *
 * 5. Due credit should be given to the Exolab Project
 *    (http://www.exolab.org/).
 *
 * THIS SOFTWARE IS PROVIDED BY EXOFFICE TECHNOLOGIES AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
 * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
 * EXOFFICE TECHNOLOGIES OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Copyright 2001-2005 (C) Exoffice Technologies Inc. All Rights Reserved.
 *
 * $Id: QueueConsumerEndpoint.java,v 1.2 2005/03/18 03:58:39 tanderson Exp $
 */
package org.exolab.jms.messagemgr;

import java.rmi.RemoteException;
import java.sql.Connection;
import javax.jms.InvalidSelectorException;
import javax.jms.JMSException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.exolab.jms.client.JmsQueue;
import org.exolab.jms.message.MessageImpl;
import org.exolab.jms.scheduler.Scheduler;
import org.exolab.jms.server.JmsServerSession;


/**
 * A {@link ConsumerEndpoint} for queues. This object shares access to a
 * particular queue with other QueueConsumerEndpoint instances.
 *
 * @author <a href="mailto:[e-mail]">Jim Alateras</a>
 * @author <a href="mailto:[e-mail]">Tim Anderson</a>
 * @version $Revision: 1.2 $ $Date: 2005/03/18 03:58:39 $
 */
public class QueueConsumerEndpoint
        extends AbstractConsumerEndpoint {

    /**
     * The destination that this consumer subscribes to.
     */
    private QueueDestinationCache _cache = null;

    /**
     * The maximum number of messages that a dispatch can deliver at any one
     * time.
     */
    private final int MAX_MESSAGES = 200;

    /**
     * The logger.
     */
    private static final Log _log =
            LogFactory.getLog(QueueConsumerEndpoint.class);


    /**
     * Construct a new <code>QueueConsumerEndpoint</code>.
     *
     * @param consumerId the identity of this consumer
     * @param session    the owning session
     * @param queue      the queue to access
     * @param scheduler  used to schedule asynchronous message delivery.
     * @throws InvalidSelectorException if the selector is not well formed
     * @throws JMSException             if the destination cache can't be
     *                                  created
     */
    public QueueConsumerEndpoint(long consumerId, JmsServerSession session,
                                 JmsQueue queue, String selector,
                                 Scheduler scheduler)
            throws InvalidSelectorException, JMSException {
        super(consumerId, session, queue, selector, false, scheduler);

        // register the endpoint with the destination cache. If
        // the destination cache does not exist then create it.
        _cache = (QueueDestinationCache)
                DestinationManager.instance().getDestinationCache(queue);
        _cache.addConsumer(this);
    }

    /**
     * Return the number of unsent messages.
     *
     * @return the number of unsent messages
     */
    public int getMessageCount() {
        return _cache.getMessageCount();
    }

    // override ConsumerEndpoint.setMessageListener
    public void setMessageListener(ConsumerEndpointListener listener) {
        // if the listener is null we unregister from the destination. If
        // the listener is not null then we register with it. When we
        // unregister we need to determine what happens to any messages
        // in the sent and
        if (listener == null) {
            _cache.removeConsumer(this);
        } else {
            _cache.addConsumer(this);
        }

        super.setMessageListener(listener);
    }

    /**
     * Return the next available message to the client.
     * <p/>
     * The <code>wait</code> parameter indicates how many milliseconds to wait
     * for a message before returning. If <code>wait</code> is <code>0</code>
     * then do not wait. If <code>wait</code> is <code>-1</code> then wait
     * indefinitely for the next message.
     *
     * @param wait number of milliseconds to wait
     * @return the next message or <code>null</code>
     * @throws JMSException for any error
     */
    public MessageHandle receive(long wait) throws JMSException {
        MessageHandle handle = getMessageFromCache();
        if (handle == null && wait >= 0) {
            // set a flag indicating that we are waiting
            // for a message
            setWaitingForMessage();

            // perform a double check and we receive a
            // message then clear the previous set flag
            handle = getMessageFromCache();
            if (handle != null) {
                clearWaitingForMessage();
            }
        }

        return handle;
    }

    /**
     * Check whether a listener has been registered with this endpoint to
     * support async message delivery
     *
     * @return boolean - true if it has
     */
    public boolean hasMessageListener() {
        return _listener != null;
    }

    /**
     * This event is called when a non-persistent message is added to a
     * <code>DestinationCache</code>.
     *
     * @param handle  a handle to the added message
     * @param message the added message
     * @return <code>true</code> if the listener accepted the message; otherwise
     *         <code>false</ode>
     */
    public boolean messageAdded(MessageHandle handle, MessageImpl message) {
        if (_listener != null) {
            schedule();
        } else {
            // notify the consumer
            notifyMessageAvailable();
        }

        return true;
    }

    /**
     * This event is called when a persistent message is added to the
     * <code>DestinationCache</code>.
     *
     * @param handle     a handle to the added message
     * @param message    the added message
     * @param connection the database connection
     * @return <code>true</code>
     */
    public boolean persistentMessageAdded(MessageHandle handle,
                                          MessageImpl message,
                                          Connection connection) {
        return messageAdded(handle, message);
    }

    /**
     * This event is called when a message is removed from the
     * <code>DestinationCache</code>.
     *
     * @param messageId the identifier of the removed message
     */
    public void messageRemoved(String messageId) {
        // no-op
    }

    /**
     * This event is called when a message is removed from the
     * <code>DestinationCache</code>
     *
     * @param messageId     a handle to the removed message
     * @param connection the database connection
     */
    public void persistentMessageRemoved(String messageId,
                                         Connection connection) {
        // no-op
    }

    /**
     * Deliver messages in the cache to the consumer
     *
     * @return <code>true</code> if the endpoint should be rescheduled
     */
    protected boolean deliverMessages() {
        boolean reschedule = true;

        for (int index = 0; index < MAX_MESSAGES; index++) {
            // check if we should exit the loop
            if (stopDelivery()) {
                reschedule = false;
                break;
            }

            MessageHandle handle = null;
            try {
                handle = getMessageFromCache();
            } catch (Exception exception) {
                _log.error(exception, exception);
            }

            // if the handle is null, then there are no more messages
            // to deliver so break
            if (handle == null) {
                reschedule = false;
                break;
            }

            try {
                // deliver the message to the client
                _listener.onMessage(handle);
            } catch (RemoteException exception) {
                // failed to deliver due to network error
                _log.error(exception, exception);
                if (handle != null) {
                    _cache.returnMessageHandle(handle);
                }
                _listener = null;
            } catch (Exception exception) {
                _log.error(exception, exception);
                if (handle != null) {
                    _cache.returnMessageHandle(handle);
                }
            }
        }
        return reschedule;
    }

    /**
     * Closes this endpoint
     */
    protected void doClose() {
        // unregister from the DestinationCache
        _cache.removeConsumer(this);
    }

    /**
     * Return a message from the corresponding cache for this consumer or null
     * if one is not available
     *
     * @return MessageHandle - the handle or null
     * @throws JMSException for any error
     */
    private MessageHandle getMessageFromCache() throws JMSException {
        MessageHandle handle = _cache.getMessage(getSelector());
        if (handle instanceof QueueConsumerMessageHandle) {
            // associate the handle with the consumer
            ((QueueConsumerMessageHandle) handle).setConsumerId(getId());
        }

        return handle;
    }

}