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STOMP-JMS is a JMS implementation using STOMP as the wire protocol
/**
* Copyright (C) 2010-2011, FuseSource Corp. All rights reserved.
*
* http://fusesource.com
*
* The software in this package is published under the terms of the
* CDDL license a copy of which has been included with this distribution
* in the license.txt file.
*/
package org.fusesource.stompjms;
import org.fusesource.hawtbuf.AsciiBuffer;
import org.fusesource.stompjms.message.StompJmsMessage;
import javax.jms.IllegalStateException;
import javax.jms.*;
import java.util.Enumeration;
import java.util.concurrent.atomic.AtomicBoolean;
import static org.fusesource.stompjms.channel.Stomp.*;
/**
* A client uses a QueueBrowser object to look at messages on a
* queue without removing them.
*
* The getEnumeration method returns a
* java.util.Enumeration
* 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.
*
* 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.
*
* A QueueBrowser can be created from either a Session
*
* or a QueueSession.
*
* @see javax.jms.Session#createBrowser
* @see javax.jms.QueueSession#createBrowser
* @see javax.jms.QueueBrowser
* @see javax.jms.QueueReceiver
*/
public class StompJmsQueueBrowser implements QueueBrowser, Enumeration {
private final StompJmsSession session;
private final StompJmsDestination destination;
private final String selector;
private StompJmsMessageConsumer consumer;
private boolean closed;
private final AsciiBuffer id;
private final AtomicBoolean browseDone = new AtomicBoolean(true);
private Object semaphore = new Object();
/**
* Constructor for an StompJmsQueueBrowser - used internally
*
* @param session
* @param id
* @param destination
* @param selector
* @throws javax.jms.JMSException
*/
protected StompJmsQueueBrowser(StompJmsSession session, AsciiBuffer id, StompJmsDestination destination, String selector) throws JMSException {
this.session = session;
this.id = id;
this.destination = destination;
this.selector = selector;
this.consumer = createConsumer();
}
private StompJmsMessageConsumer createConsumer() throws JMSException {
browseDone.set(false);
StompJmsMessageConsumer rc = new StompJmsMessageConsumer(id, session, destination, selector) {
@Override
public boolean isBrowser() {
return true;
}
public void onMessage(StompJmsMessage message) {
if (message == null) {
browseDone.set(true);
} else {
AsciiBuffer browser = message.getFrame().headers.get(BROWSER);
if (browser!=null && END.equals(browser)) {
browseDone.set(true);
} else {
super.onMessage(message);
}
}
notifyMessageAvailable();
}
};
rc.init();
return rc;
}
private void destroyConsumer() {
if (consumer == null) {
return;
}
try {
if (session.getTransacted()) {
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 javax.jms.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.getMessageQueueSize() > 0) {
return true;
}
if (browseDone.get() || !session.isStarted()) {
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.getConnection().onException(e);
return null;
}
if (browseDone.get() || !session.isStarted()) {
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 javax.jms.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.
*/
protected void waitForMessage() {
try {
synchronized (semaphore) {
semaphore.wait(2000);
}
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
}
protected void notifyMessageAvailable() {
synchronized (semaphore) {
semaphore.notifyAll();
}
}
public String toString() {
return "StompJmsQueueBrowser { value=" + this.id + " }";
}
}