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ActiveMQ example source code file (ActiveMQQueueBrowser.java)

This example ActiveMQ source code file (ActiveMQQueueBrowser.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - ActiveMQ tags/keywords

activemqdestination, activemqmessageconsumer, activemqqueuebrowser, activemqqueuebrowser, atomicboolean, consumerid, enumeration, jmsexception, jmsexception, object, object, queue, string, string, util

The ActiveMQ ActiveMQQueueBrowser.java source code

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.activemq;

import java.util.Enumeration;
import java.util.concurrent.atomic.AtomicBoolean;

import javax.jms.IllegalStateException;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.Queue;
import javax.jms.QueueBrowser;

import org.apache.activemq.command.ActiveMQDestination;
import org.apache.activemq.command.ConsumerId;
import org.apache.activemq.command.MessageDispatch;

/**
 * A client uses a <CODE>QueueBrowser object to look at messages on a
 * queue without removing them. <p/>
 * <P>
 * The <CODE>getEnumeration method returns a 
 * java.util.Enumeration</CODE>
 * that is used to scan the queue's messages. It may be an enumeration of the
 * entire content of a queue, or it may contain only the messages matching a
 * message selector. <p/>
 * <P>
 * Messages may be arriving and expiring while the scan is done. The JMS API
 * does not require the content of an enumeration to be a static snapshot of
 * queue content. Whether these changes are visible or not depends on the JMS
 * provider. <p/>
 * <P>
 * A <CODE>QueueBrowser can be created from either a Session
 * </CODE>
 * or a <CODE>QueueSession.
 *
 * @see javax.jms.Session#createBrowser
 * @see javax.jms.QueueSession#createBrowser
 * @see javax.jms.QueueBrowser
 * @see javax.jms.QueueReceiver
 */

public class ActiveMQQueueBrowser implements QueueBrowser, Enumeration {

    private final ActiveMQSession session;
    private final ActiveMQDestination destination;
    private final String selector;

    private ActiveMQMessageConsumer consumer;
    private boolean closed;
    private final ConsumerId consumerId;
    private final AtomicBoolean browseDone = new AtomicBoolean(true);
    private final boolean dispatchAsync;
    private Object semaphore = new Object();

    /**
     * Constructor for an ActiveMQQueueBrowser - used internally
     *
     * @param theSession
     * @param dest
     * @param selector
     * @throws JMSException
     */
    protected ActiveMQQueueBrowser(ActiveMQSession session, ConsumerId consumerId, ActiveMQDestination destination, String selector, boolean dispatchAsync) throws JMSException {
        this.session = session;
        this.consumerId = consumerId;
        this.destination = destination;
        this.selector = selector;
        this.dispatchAsync = dispatchAsync;
        this.consumer = createConsumer();
    }

    /**
     * @param session
     * @param originalDestination
     * @param selectorExpression
     * @param cnum
     * @return
     * @throws JMSException
     */
    private ActiveMQMessageConsumer createConsumer() throws JMSException {
        browseDone.set(false);
        ActiveMQPrefetchPolicy prefetchPolicy = session.connection.getPrefetchPolicy();

        return new ActiveMQMessageConsumer(session, consumerId, destination, null, selector, prefetchPolicy.getQueueBrowserPrefetch(), prefetchPolicy
            .getMaximumPendingMessageLimit(), false, true, dispatchAsync, null) {
            public void dispatch(MessageDispatch md) {
                if (md.getMessage() == null) {
                    browseDone.set(true);
                } else {
                    super.dispatch(md);
                }
                notifyMessageAvailable();
            }
        };
    }

    private void destroyConsumer() {
        if (consumer == null) {
            return;
        }
        try {
            if (session.getTransacted() && session.getTransactionContext().isInLocalTransaction()) {
                session.commit();
            }
            consumer.close();
            consumer = null;
        } catch (JMSException e) {
            e.printStackTrace();
        }
    }

    /**
     * Gets an enumeration for browsing the current queue messages in the order
     * they would be received.
     *
     * @return an enumeration for browsing the messages
     * @throws JMSException if the JMS provider fails to get the enumeration for
     *                 this browser due to some internal error.
     */

    public Enumeration getEnumeration() throws JMSException {
        checkClosed();
        if (consumer == null) {
            consumer = createConsumer();
        }
        return this;
    }

    private void checkClosed() throws IllegalStateException {
        if (closed) {
            throw new IllegalStateException("The Consumer is closed");
        }
    }

    /**
     * @return true if more messages to process
     */
    public boolean hasMoreElements() {
        while (true) {

            synchronized (this) {
                if (consumer == null) {
                    return false;
                }
            }

            if (consumer.getMessageSize() > 0) {
                return true;
            }

            if (browseDone.get() || !session.isRunning()) {
                destroyConsumer();
                return false;
            }

            waitForMessage();
        }
    }

    /**
     * @return the next message
     */
    public Object nextElement() {
        while (true) {

            synchronized (this) {
                if (consumer == null) {
                    return null;
                }
            }

            try {
                Message answer = consumer.receiveNoWait();
                if (answer != null) {
                    return answer;
                }
            } catch (JMSException e) {
                this.session.connection.onClientInternalException(e);
                return null;
            }

            if (browseDone.get() || !session.isRunning()) {
                destroyConsumer();
                return null;
            }

            waitForMessage();
        }
    }

    public synchronized void close() throws JMSException {
        destroyConsumer();
        closed = true;
    }

    /**
     * Gets the queue associated with this queue browser.
     *
     * @return the queue
     * @throws JMSException if the JMS provider fails to get the queue
     *                 associated with this browser due to some internal error.
     */

    public Queue getQueue() throws JMSException {
        return (Queue)destination;
    }

    public String getMessageSelector() throws JMSException {
        return selector;
    }

    // Implementation methods
    // -------------------------------------------------------------------------

    /**
     * Wait on a semaphore for a fixed amount of time for a message to come in.
     * @throws JMSException
     */
    protected void waitForMessage() {
        try {
            consumer.sendPullCommand(-1);
            synchronized (semaphore) {
                semaphore.wait(2000);
            }
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        } catch (JMSException e) {
        }

    }

    protected void notifyMessageAvailable() {
        synchronized (semaphore) {
            semaphore.notifyAll();
        }
    }

    public String toString() {
        return "ActiveMQQueueBrowser { value=" + consumerId + " }";
    }

}

Other ActiveMQ examples (source code examples)

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