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/**
* 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 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 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 {
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.
*/
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 "ActiveMQQueueBrowser { value=" + consumerId + " }";
}
}