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Receiving a Message

This describes how to receive messages with JMS in Spring.

Synchronous Reception

While JMS is typically associated with asynchronous processing, you can consume messages synchronously. The overloaded receive(..) methods provide this functionality. During a synchronous receive, the calling thread blocks until a message becomes available. This can be a dangerous operation, since the calling thread can potentially be blocked indefinitely. The receiveTimeout property specifies how long the receiver should wait before giving up waiting for a message.

Asynchronous reception: Message-Driven POJOs

Spring also supports annotated-listener endpoints through the use of the @JmsListener annotation and provides an open infrastructure to register endpoints programmatically. This is, by far, the most convenient way to setup an asynchronous receiver. See jms-annotated-support for more details.

In a fashion similar to a Message-Driven Bean (MDB) in the EJB world, the Message-Driven POJO (MDP) acts as a receiver for JMS messages. The one restriction (but see jms-receiving-async-message-listener-adapter) on an MDP is that it must implement the javax.jms.MessageListener interface. Note that, if your POJO receives messages on multiple threads, it is important to ensure that your implementation is thread-safe.

The following example shows a simple implementation of an MDP:

import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageListener;
import javax.jms.TextMessage;

public class ExampleListener implements MessageListener {

	public void onMessage(Message message) {
		if (message instanceof TextMessage) {
			try {
				System.out.println(((TextMessage) message).getText());
			}
			catch (JMSException ex) {
				throw new RuntimeException(ex);
			}
		}
		else {
			throw new IllegalArgumentException("Message must be of type TextMessage");
		}
	}
}

Once you have implemented your MessageListener, it is time to create a message listener container.

The following example shows how to define and configure one of the message listener containers that ships with Spring (in this case, DefaultMessageListenerContainer):

<!-- this is the Message Driven POJO (MDP) -->
<bean id="messageListener" class="jmsexample.ExampleListener"/>

<!-- and this is the message listener container -->
<bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">
	<property name="connectionFactory" ref="connectionFactory"/>
	<property name="destination" ref="destination"/>
	<property name="messageListener" ref="messageListener"/>
</bean>

See the Spring javadoc of the various message listener containers (all of which implement MessageListenerContainer) for a full description of the features supported by each implementation.

Using the `SessionAwareMessageListener` Interface

The SessionAwareMessageListener interface is a Spring-specific interface that provides a similar contract to the JMS MessageListener interface but also gives the message-handling method access to the JMS Session from which the Message was received. The following listing shows the definition of the SessionAwareMessageListener interface:

package org.springframework.jms.listener;

public interface SessionAwareMessageListener {

	void onMessage(Message message, Session session) throws JMSException;
}

You can choose to have your MDPs implement this interface (in preference to the standard JMS MessageListener interface) if you want your MDPs to be able to respond to any received messages (by using the Session supplied in the onMessage(Message, Session) method). All of the message listener container implementations that ship with Spring have support for MDPs that implement either the MessageListener or SessionAwareMessageListener interface. Classes that implement the SessionAwareMessageListener come with the caveat that they are then tied to Spring through the interface. The choice of whether or not to use it is left entirely up to you as an application developer or architect.

Note that the onMessage(..) method of the SessionAwareMessageListener interface throws JMSException. In contrast to the standard JMS MessageListener interface, when using the SessionAwareMessageListener interface, it is the responsibility of the client code to handle any thrown exceptions.

Using `MessageListenerAdapter`

The MessageListenerAdapter class is the final component in Spring’s asynchronous messaging support. In a nutshell, it lets you expose almost any class as an MDP (though there are some constraints).

Consider the following interface definition:

public interface MessageDelegate {

	void handleMessage(String message);

	void handleMessage(Map message);

	void handleMessage(byte[] message);

	void handleMessage(Serializable message);
}

Notice that, although the interface extends neither the MessageListener nor the SessionAwareMessageListener interface, you can still use it as an MDP by using the MessageListenerAdapter class. Notice also how the various message handling methods are strongly typed according to the contents of the various Message types that they can receive and handle.

Now consider the following implementation of the MessageDelegate interface:

public class DefaultMessageDelegate implements MessageDelegate {
	// implementation elided for clarity...
}

In particular, note how the preceding implementation of the MessageDelegate interface (the DefaultMessageDelegate class) has no JMS dependencies at all. It truly is a POJO that we can make into an MDP through the following configuration:

<!-- this is the Message Driven POJO (MDP) -->
<bean id="messageListener" class="org.springframework.jms.listener.adapter.MessageListenerAdapter">
	<constructor-arg>
		<bean class="jmsexample.DefaultMessageDelegate"/>
	</constructor-arg>
</bean>

<!-- and this is the message listener container... -->
<bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">
	<property name="connectionFactory" ref="connectionFactory"/>
	<property name="destination" ref="destination"/>
	<property name="messageListener" ref="messageListener"/>
</bean>

The next example shows another MDP that can handle only receiving JMS TextMessage messages. Notice how the message handling method is actually called receive (the name of the message handling method in a MessageListenerAdapter defaults to handleMessage), but it is configurable (as you can see later in this section). Notice also how the receive(..) method is strongly typed to receive and respond only to JMS TextMessage messages. The following listing shows the definition of the TextMessageDelegate interface:

public interface TextMessageDelegate {

	void receive(TextMessage message);
}

The following listing shows a class that implements the TextMessageDelegate interface:

public class DefaultTextMessageDelegate implements TextMessageDelegate {
	// implementation elided for clarity...
}

The configuration of the attendant MessageListenerAdapter would then be as follows:

<bean id="messageListener" class="org.springframework.jms.listener.adapter.MessageListenerAdapter">
	<constructor-arg>
		<bean class="jmsexample.DefaultTextMessageDelegate"/>
	</constructor-arg>
	<property name="defaultListenerMethod" value="receive"/>
	<!-- we don't want automatic message context extraction -->
	<property name="messageConverter">
		<null/>
	</property>
</bean>

Note that, if the messageListener receives a JMS Message of a type other than TextMessage, an IllegalStateException is thrown (and subsequently swallowed). Another of the capabilities of the MessageListenerAdapter class is the ability to automatically send back a response Message if a handler method returns a non-void value. Consider the following interface and class:

public interface ResponsiveTextMessageDelegate {

	// notice the return type...
	String receive(TextMessage message);
}

public class DefaultResponsiveTextMessageDelegate implements ResponsiveTextMessageDelegate {
	// implementation elided for clarity...
}

If you use the DefaultResponsiveTextMessageDelegate in conjunction with a MessageListenerAdapter, any non-null value that is returned from the execution of the 'receive(..)' method is (in the default configuration) converted into a TextMessage. The resulting TextMessage is then sent to the Destination (if one exists) defined in the JMS Reply-To property of the original Message or the default Destination set on the MessageListenerAdapter (if one has been configured). If no Destination is found, an InvalidDestinationException is thrown (note that this exception is not swallowed and propagates up the call stack).

Processing Messages Within Transactions

Invoking a message listener within a transaction requires only reconfiguration of the listener container.

You can activate local resource transactions through the sessionTransacted flag on the listener container definition. Each message listener invocation then operates within an active JMS transaction, with message reception rolled back in case of listener execution failure. Sending a response message (through SessionAwareMessageListener) is part of the same local transaction, but any other resource operations (such as database access) operate independently. This usually requires duplicate message detection in the listener implementation, to cover the case where database processing has committed but message processing failed to commit.

Consider the following bean definition:

<bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">
	<property name="connectionFactory" ref="connectionFactory"/>
	<property name="destination" ref="destination"/>
	<property name="messageListener" ref="messageListener"/>
	<property name="sessionTransacted" value="true"/>
</bean>

To participate in an externally managed transaction, you need to configure a transaction manager and use a listener container that supports externally managed transactions (typically, DefaultMessageListenerContainer).

To configure a message listener container for XA transaction participation, you want to configure a JtaTransactionManager (which, by default, delegates to the Java EE server’s transaction subsystem). Note that the underlying JMS ConnectionFactory needs to be XA-capable and properly registered with your JTA transaction coordinator. (Check your Java EE server’s configuration of JNDI resources.) This lets message reception as well as (for example) database access be part of the same transaction (with unified commit semantics, at the expense of XA transaction log overhead).

The following bean definition creates a transaction manager:

<bean id="transactionManager" class="org.springframework.transaction.jta.JtaTransactionManager"/>

Then we need to add it to our earlier container configuration. The container takes care of the rest. The following example shows how to do so:

<bean id="jmsContainer" class="org.springframework.jms.listener.DefaultMessageListenerContainer">
	<property name="connectionFactory" ref="connectionFactory"/>
	<property name="destination" ref="destination"/>
	<property name="messageListener" ref="messageListener"/>
	<property name="transactionManager" ref="transactionManager"/> (1)
</bean>

1	Our transaction manager.