/*
 * Copyright 2002-2008 the original author or authors.
 *
 * Licensed 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.springframework.jms.listener;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

import javax.jms.Connection;
import javax.jms.Destination;
import javax.jms.ExceptionListener;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageConsumer;
import javax.jms.MessageListener;
import javax.jms.Session;
import javax.jms.Topic;

import org.springframework.core.task.TaskExecutor;
import org.springframework.jms.support.JmsUtils;
import org.springframework.transaction.support.TransactionSynchronizationManager;
import org.springframework.util.Assert;

/**
 * Message listener container that uses the plain JMS client API's
 * <code>MessageConsumer.setMessageListener()</code> method to
 * create concurrent MessageConsumers for the specified listeners.
 *
 * <p><b>NOTE:</b> This class requires a JMS 1.1+ provider, because it builds on
 * the domain-independent API. <b>Use the {@link SimpleMessageListenerContainer102}
 * subclass for a JMS 1.0.2 provider, e.g. when running on a J2EE 1.3 server.</b>
 *
 * <p>This is the simplest form of a message listener container.
 * It creates a fixed number of JMS Sessions to invoke the listener,
 * not allowing for dynamic adaptation to runtime demands. Its main
 * advantage is its low level of complexity and the minimum requirements
 * on the JMS provider: Not even the ServerSessionPool facility is required.
 *
 * <p>See the {@link AbstractMessageListenerContainer} javadoc for details
 * on acknowledge modes and transaction options.
 *
 * <p>For a different style of MessageListener handling, through looped
 * <code>MessageConsumer.receive()</code> calls that also allow for
 * transactional reception of messages (registering them with XA transactions),
 * see {@link DefaultMessageListenerContainer}.
 *
 * @author Juergen Hoeller
 * @since 2.0
 * @see javax.jms.MessageConsumer#setMessageListener
 * @see DefaultMessageListenerContainer
 * @see org.springframework.jms.listener.endpoint.JmsMessageEndpointManager
 */
public class SimpleMessageListenerContainer extends AbstractMessageListenerContainer implements ExceptionListener {

	private boolean pubSubNoLocal = false;

	private int concurrentConsumers = 1;

	private TaskExecutor taskExecutor;

	private Set sessions;

	private Set consumers;

	private final Object consumersMonitor = new Object();


	/**
	 * Set whether to inhibit the delivery of messages published by its own connection.
	 * Default is "false".
	 * @see javax.jms.TopicSession#createSubscriber(javax.jms.Topic, String, boolean)
	 */
	public void setPubSubNoLocal(boolean pubSubNoLocal) {
		this.pubSubNoLocal = pubSubNoLocal;
	}

	/**
	 * Return whether to inhibit the delivery of messages published by its own connection.
	 */
	protected boolean isPubSubNoLocal() {
		return this.pubSubNoLocal;
	}

	/**
	 * Specify the number of concurrent consumers to create. Default is 1.
	 * <p>Raising the number of concurrent consumers is recommendable in order
	 * to scale the consumption of messages coming in from a queue. However,
	 * note that any ordering guarantees are lost once multiple consumers are
	 * registered. In general, stick with 1 consumer for low-volume queues.
	 * <p><b>Do not raise the number of concurrent consumers for a topic.</b>
	 * This would lead to concurrent consumption of the same message,
	 * which is hardly ever desirable.
	 */
	public void setConcurrentConsumers(int concurrentConsumers) {
		Assert.isTrue(concurrentConsumers > 0, "'concurrentConsumers' value must be at least 1 (one)");
		this.concurrentConsumers = concurrentConsumers;
	}

	/**
	 * Set the Spring TaskExecutor to use for executing the listener once
	 * a message has been received by the provider.
	 * <p>Default is none, that is, to run in the JMS provider's own receive thread,
	 * blocking the provider's receive endpoint while executing the listener.
	 * <p>Specify a TaskExecutor for executing the listener in a different thread,
	 * rather than blocking the JMS provider, usually integrating with an existing
	 * thread pool. This allows to keep the number of concurrent consumers low (1)
	 * while still processing messages concurrently (decoupled from receiving!).
	 * <p><b>NOTE: Specifying a TaskExecutor for listener execution affects
	 * acknowledgement semantics.</b> Messages will then always get acknowledged
	 * before listener execution, with the underlying Session immediately reused
	 * for receiving the next message. Using this in combination with a transacted
	 * session or with client acknowledgement will lead to unspecified results!
	 * <p><b>NOTE: Concurrent listener execution via a TaskExecutor will lead
	 * to concurrent processing of messages that have been received by the same
	 * underlying Session.</b> As a consequence, it is not recommended to use
	 * this setting with a {@link SessionAwareMessageListener}, at least not
	 * if the latter performs actual work on the given Session. A standard
	 * {@link javax.jms.MessageListener} will work fine, in general.
	 * @see #setConcurrentConsumers
	 * @see org.springframework.core.task.SimpleAsyncTaskExecutor
	 * @see org.springframework.scheduling.commonj.WorkManagerTaskExecutor
	 */
	public void setTaskExecutor(TaskExecutor taskExecutor) {
		this.taskExecutor = taskExecutor;
	}

	protected void validateConfiguration() {
		super.validateConfiguration();
		if (isSubscriptionDurable() && this.concurrentConsumers != 1) {
			throw new IllegalArgumentException("Only 1 concurrent consumer supported for durable subscription");
		}
	}


	//-------------------------------------------------------------------------
	// Implementation of AbstractMessageListenerContainer's template methods
	//-------------------------------------------------------------------------

	/**
	 * Always use a shared JMS Connection.
	 */
	protected final boolean sharedConnectionEnabled() {
		return true;
	}

	/**
	 * Creates the specified number of concurrent consumers,
	 * in the form of a JMS Session plus associated MessageConsumer.
	 * @see #createListenerConsumer
	 */
	protected void doInitialize() throws JMSException {
		establishSharedConnection();
		initializeConsumers();
	}

	/**
	 * Re-initializes this container's JMS message consumers,
	 * if not initialized already.
	 */
	protected void doStart() throws JMSException {
		super.doStart();
		initializeConsumers();
	}

	/**
	 * Registers this listener container as JMS ExceptionListener on the shared connection.
	 */
	protected void prepareSharedConnection(Connection connection) throws JMSException {
		super.prepareSharedConnection(connection);
		connection.setExceptionListener(this);
	}

	/**
	 * JMS ExceptionListener implementation, invoked by the JMS provider in
	 * case of connection failures. Re-initializes this listener container's
	 * shared connection and its sessions and consumers.
	 * @param ex the reported connection exception
	 */
	public void onException(JMSException ex) {
		// First invoke the user-specific ExceptionListener, if any.
		invokeExceptionListener(ex);

		// Now try to recover the shared Connection and all consumers...
		if (logger.isInfoEnabled()) {
			logger.info("Trying to recover from JMS Connection exception: " + ex);
		}
		try {
			synchronized (this.consumersMonitor) {
				this.sessions = null;
				this.consumers = null;
			}
			refreshSharedConnection();
			initializeConsumers();
			logger.info("Successfully refreshed JMS Connection");
		}
		catch (JMSException recoverEx) {
			logger.debug("Failed to recover JMS Connection", recoverEx);
			logger.error("Encountered non-recoverable JMSException", ex);
		}
	}

	/**
	 * Initialize the JMS Sessions and MessageConsumers for this container.
	 * @throws JMSException in case of setup failure
	 */
	protected void initializeConsumers() throws JMSException {
		// Register Sessions and MessageConsumers.
		synchronized (this.consumersMonitor) {
			if (this.consumers == null) {
				this.sessions = new HashSet(this.concurrentConsumers);
				this.consumers = new HashSet(this.concurrentConsumers);
				Connection con = getSharedConnection();
				for (int i = 0; i < this.concurrentConsumers; i++) {
					Session session = createSession(con);
					MessageConsumer consumer = createListenerConsumer(session);
					this.sessions.add(session);
					this.consumers.add(consumer);
				}
			}
		}
	}

	/**
	 * Create a MessageConsumer for the given JMS Session,
	 * registering a MessageListener for the specified listener.
	 * @param session the JMS Session to work on
	 * @return the MessageConsumer
	 * @throws JMSException if thrown by JMS methods
	 * @see #executeListener
	 */
	protected MessageConsumer createListenerConsumer(final Session session) throws JMSException {
		Destination destination = getDestination();
		if (destination == null) {
			destination = resolveDestinationName(session, getDestinationName());
		}
		MessageConsumer consumer = createConsumer(session, destination);

		if (this.taskExecutor != null) {
			consumer.setMessageListener(new MessageListener() {
				public void onMessage(final Message message) {
					taskExecutor.execute(new Runnable() {
						public void run() {
							processMessage(message, session);
						}
					});
				}
			});
		}
		else {
			consumer.setMessageListener(new MessageListener() {
				public void onMessage(Message message) {
					processMessage(message, session);
				}
			});
		}

		return consumer;
	}

	/**
	 * Process a message received from the provider.
	 * <p>Executes the listener, exposing the current JMS Session as
	 * thread-bound resource (if "exposeListenerSession" is "true").
	 * @param message the received JMS Message
	 * @param session the JMS Session to operate on
	 * @see #executeListener
	 * @see #setExposeListenerSession
	 */
	protected void processMessage(Message message, Session session) {
		boolean exposeResource = isExposeListenerSession();
		if (exposeResource) {
			TransactionSynchronizationManager.bindResource(
					getConnectionFactory(), new LocallyExposedJmsResourceHolder(session));
		}
		try {
			executeListener(session, message);
		}
		finally {
			if (exposeResource) {
				TransactionSynchronizationManager.unbindResource(getConnectionFactory());
			}
		}
	}

	/**
	 * Destroy the registered JMS Sessions and associated MessageConsumers.
	 */
	protected void doShutdown() throws JMSException {
		logger.debug("Closing JMS MessageConsumers");
		for (Iterator it = this.consumers.iterator(); it.hasNext();) {
			MessageConsumer consumer = (MessageConsumer) it.next();
			JmsUtils.closeMessageConsumer(consumer);
		}
		logger.debug("Closing JMS Sessions");
		for (Iterator it = this.sessions.iterator(); it.hasNext();) {
			Session session = (Session) it.next();
			JmsUtils.closeSession(session);
		}
	}


	//-------------------------------------------------------------------------
	// JMS 1.1 factory methods, potentially overridden for JMS 1.0.2
	//-------------------------------------------------------------------------

	/**
	 * Create a JMS MessageConsumer for the given Session and Destination.
	 * <p>This implementation uses JMS 1.1 API.
	 * @param session the JMS Session to create a MessageConsumer for
	 * @param destination the JMS Destination to create a MessageConsumer for
	 * @return the new JMS MessageConsumer
	 * @throws JMSException if thrown by JMS API methods
	 */
	protected MessageConsumer createConsumer(Session session, Destination destination) throws JMSException {
		// Only pass in the NoLocal flag in case of a Topic:
		// Some JMS providers, such as WebSphere MQ 6.0, throw IllegalStateException
		// in case of the NoLocal flag being specified for a Queue.
		if (isPubSubDomain()) {
			if (isSubscriptionDurable() && destination instanceof Topic) {
				return session.createDurableSubscriber(
						(Topic) destination, getDurableSubscriptionName(), getMessageSelector(), isPubSubNoLocal());
			}
			else {
				return session.createConsumer(destination, getMessageSelector(), isPubSubNoLocal());
			}
		}
		else {
			return session.createConsumer(destination, getMessageSelector());
		}
	}

}
