<?xml version="1.0" encoding="UTF-8"?>
<chapter xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="jms"
    xmlns:xlink="http://www.w3.org/1999/xlink">
  <title>JMS Support</title>
  <para>
    Spring Integration provides Channel Adapters for receiving and sending JMS messages. There are actually two
    JMS-based inbound Channel Adapters. The first uses Spring's <classname>JmsTemplate</classname> to receive based on
    a polling period. The second is "message-driven" and relies upon a Spring MessageListener container. There is also
    an outbound Channel Adapter which uses the <classname>JmsTemplate</classname> to convert and send a JMS Message on
    demand.
  </para>
  <para>
  As you can see from above by using <classname>JmsTemplate</classname> and <classname>MessageListener</classname> container Spring Integration relies on Spring's JMS support.
  This is important to understand since most of the attributes exposed on these adapters will configure the underlying Spring's <classname>JmsTemplate</classname> and/or 
  <classname>MessageListener</classname> container. For more details about <classname>JmsTemplate</classname> and <classname>MessageListener</classname> container please refer to 
  <ulink url="http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/jms.html">Spring JMS documentation</ulink>.
  </para>
  <para>
    Whereas the JMS Channel Adapters are intended for unidirectional Messaging (send-only or receive-only), Spring
    Integration also provides inbound and outbound JMS Gateways for request/reply operations. The inbound gateway
    relies on one of Spring's MessageListener container implementations for Message-driven reception that is also
    capable of sending a return value to the "reply-to" Destination as provided by the received Message. The outbound
    Gateway sends a JMS Message to a "request-destination" and then receives a reply Message. The "reply-destination"
    reference (or "reply-destination-name") can be configured explicitly or else the outbound gateway will use a
    JMS TemporaryQueue.
  </para>

  <section id="jms-inbound-channel-adapter">
    <title>Inbound Channel Adapter</title>
    <para>
      The inbound Channel Adapter requires a reference to either a single <classname>JmsTemplate</classname>
      instance or both <interfacename>ConnectionFactory</interfacename> and <interfacename>Destination</interfacename>
      (a 'destinationName' can be provided in place of the 'destination' reference). The following example defines an
      inbound Channel Adapter with a <classname>Destination</classname> reference.
      <programlisting language="xml"><![CDATA[ <jms:inbound-channel-adapter id="jmsIn" destination="inQueue" channel="exampleChannel">
     <integration:poller fixed-rate="30000"/>
 </jms:inbound-channel-adapter>]]></programlisting>
      <tip>
        Notice from the configuration that the inbound-channel-adapter is a Polling Consumer. That means that
        it invokes receive() when triggered. This should only be used in situations where polling is done relatively
        infrequently and timeliness is not important. For all other situations (a vast majority of JMS-based use-cases),
        the <emphasis>message-driven-channel-adapter</emphasis> described below is a better option.
      </tip>
      <note>
        All of the JMS adapters that require a reference to the ConnectionFactory will automatically look for
        a bean named "connectionFactory" by default. That is why you don't see a "connection-factory" attribute
        in many of the examples. However, if your JMS ConnectionFactory has a different bean name, then you will
        need to provide that attribute.
      </note>
    </para>
    <para>
      If 'extract-payload' is set to true (which is the default), the received JMS Message will be passed through
      the MessageConverter. When relying on the default SimpleMessageConverter, this means that the resulting Spring
      Integration Message will have the JMS Message's body as its payload. A JMS TextMessage will produce a
      String-based payload, a JMS BytesMessage will produce a byte array payload, and a JMS ObjectMessage's
      Serializable instance will become the Spring Integration Message's payload. If instead you prefer to have
      the raw JMS Message as the Spring Integration Message's payload, then set 'extract-payload' to false.
      <programlisting language="xml"><![CDATA[ <jms:inbound-channel-adapter id="jmsIn"
                              destination="inQueue"
                              channel="exampleChannel"
                              extract-payload="false"/>
     <integration:poller fixed-rate="30000"/>
 </jms:inbound-channel-adapter>]]></programlisting>
    </para>
  </section>

  <section id="jms-message-driven-channel-adapter">
    <title>Message-Driven Channel Adapter</title>
    <para>
      The "message-driven-channel-adapter" requires a reference to either an instance of a Spring MessageListener
      container (any subclass of <classname>AbstractMessageListenerContainer</classname>) or both  
      <interfacename>ConnectionFactory</interfacename> and <interfacename>Destination</interfacename>
      (a 'destinationName' can be provided in place of the 'destination' reference). The following example defines a
      message-driven Channel Adapter with a <classname>Destination</classname> reference.
      <programlisting language="xml"><![CDATA[ <jms:message-driven-channel-adapter id="jmsIn" destination="inQueue" channel="exampleChannel"/>]]></programlisting>
      <note>
        The Message-Driven adapter also accepts several properties that pertain to the MessageListener container.
        These values are only considered if you do not provide an actual 'container' reference. In that case,
        an instance of DefaultMessageListenerContainer will be created and configured based on these properties.
        For example, you can specify the "transaction-manager" reference, the "concurrent-consumers" value, and
        several other property references and values. Refer to the JavaDoc and Spring Integration's JMS Schema
        (spring-integration-jms-2.0.xsd) for more detail.
      </note>
    </para>
    <para>
      The 'extract-payload' property has the same effect as described above, and once again its default value
      is 'true'. The poller sub-element is not applicable for a message-driven
      Channel Adapter, as it will be actively invoked. For most usage scenarios, the message-driven approach is better since the Messages will
      be passed along to the <interfacename>MessageChannel</interfacename> as soon as they are received from the underlying
      JMS consumer.
    </para>
    <para>Finally, the &lt;message-driven-channel-adapter&gt; also accepts the 'error-channel' attribute. This
      provides the same basic functionality as described in <xref linkend="gateway-proxy"/>.
<programlisting language="xml"><![CDATA[ <jms:message-driven-channel-adapter id="jmsIn" destination="inQueue" 
         channel="exampleChannel"
         error-channel="exampleErrorChannel"/>
]]></programlisting>
	      When comparing this to the generic gateway configuration, or the JMS 'inbound-gateway' that will
          be discussed below, the key difference here is that we are in a one-way flow
          since this is a 'channel-adapter', not a gateway. Therefore, the flow downstream from the
          'error-channel' should also be one-way. For example, it could simply send to a logging handler,
          or it could be connected to a different JMS &lt;outbound-channel-adapter&gt; element.
      </para>
  </section>

  <section id="jms-outbound-channel-adapter">
    <title>Outbound Channel Adapter</title>
    <para>
      The <classname>JmsSendingMessageHandler</classname> implements the <interfacename>MessageHandler</interfacename>
      interface and is capable of converting Spring Integration <interfacename>Messages</interfacename> to JMS messages
      and then sending to a JMS destination. It requires either a 'jmsTemplate' reference or both 'connectionFactory' and
      'destination' references (again, the 'destinationName' may be provided in place of the 'destination'). As with the
      inbound Channel Adapter, the easiest way to configure this adapter is with the namespace support. The following
      configuration will produce an adapter that receives Spring Integration Messages from the "exampleChannel" and then
      converts those into JMS Messages and sends them to the JMS Destination reference whose bean name is "outQueue".
      <programlisting language="xml"><![CDATA[<jms:outbound-channel-adapter id="jmsOut" destination="outQueue" channel="exampleChannel"/>]]></programlisting>
    </para>
    <para>
      As with the inbound Channel Adapters, there is an 'extract-payload' property. However, the meaning is reversed
      for the outbound adapter. Rather than applying to the JMS Message, the boolean property applies to the Spring
      Integration Message payload. In other words, the decision is whether to pass the Spring Integration Message
      <emphasis>itself</emphasis> as the JMS Message body or whether to pass the Spring Integration Message's
      payload as the JMS Message body. The default value is once again 'true'. Therefore, if you pass a Spring
      Integration Message whose payload is a String, a JMS TextMessage will be created. If on the other hand you
      want to send the actual Spring Integration Message to another system via JMS, then simply set this to 'false'.
      <note>
        Regardless of the boolean value for payload extraction, the Spring Integration MessageHeaders will map to
        JMS properties as long as you are relying on the default converter or provide a reference to another
        instance of HeaderMappingMessageConverter (the same holds true for 'inbound' adapters except that in
        those cases, it's the JMS properties mapping <emphasis>to</emphasis> Spring Integration MessageHeaders).
      </note>
    </para>
  </section>

  <section id="jms-inbound-gateway">
    <title>Inbound Gateway</title>
    <para>
      Spring Integration's message-driven JMS inbound-gateway delegates to a
      <interfacename>MessageListener</interfacename> container, supports dynamically adjusting concurrent consumers,
      and can also handle replies. The inbound gateway requires references to a
      <interfacename>ConnectionFactory</interfacename>, and a request <interfacename>Destination</interfacename> (or
      'requestDestinationName'). The following example defines a JMS "inbound-gateway" that receives from the JMS
      queue referenced by the bean id "inQueue" and sends to the Spring Integration channel named "exampleChannel".
      <programlisting language="xml"><![CDATA[ <jms:inbound-gateway id="jmsInGateway"
                      request-destination="inQueue"
                      request-channel="exampleChannel"/>]]></programlisting>
    </para>
    <para>
      Since the gateways provide request/reply behavior instead of unidirectional send <emphasis>or</emphasis>
      receive, they also have two distinct properties for the "payload extraction" (as discussed above for the
      Channel Adapters' 'extract-payload' setting). For an inbound-gateway, the 'extract-request-payload' property
      determines whether the received JMS Message body will be extracted. If 'false', the JMS Message itself will
      become the Spring Integration Message payload. The default is 'true'.
    </para>
    <para>
      Similarly, for an inbound-gateway the 'extract-reply-payload' property applies to the Spring Integration Message
      that is going to be converted into a reply JMS Message. If you want to pass the whole Spring Integration Message
      (as the body of a JMS ObjectMessage) then set this to 'false'. By default, it is also 'true' such that the Spring
      Integration Message <emphasis>payload</emphasis> will be converted into a JMS Message (e.g. String payload
      becomes a JMS TextMessage).
    </para>
    <para>
    As with anything else, Gateway invocation might result in error.
    By default Producer will not be notified of the errors that might have occurred on the consumer side and will time out waiting for 
    the reply. However there might be times when you want to communicate an error condition back to the consumer, 
    in other words treat the Exception as a valid reply by mapping it to a Message. To accomplish this 
    JMS Inbound Gateway provides support for a Message Channel to which errors
    can be sent for processing, potentially resulting in a reply Message payload
    that conforms to some contract defining what a caller may expect as an "error"
    reply. Such a channel can be configured via the <emphasis>error-channel</emphasis>
    attribute.

<programlisting language="xml"><![CDATA[<int-jms:inbound-gateway request-destination="requestQueue" 
          request-channel="jmsinputchannel"
          error-channel="errorTransformationChannel"/>

<si:transformer input-channel="exceptionTransformationChannel"
        ref="exceptionTransformer" method="createErrorResponse"/>
]]></programlisting>
      You might notice that this example looks very similar to that included
      within <xref linkend="gateway-proxy"/>.
	  The same idea applies here: The <emphasis>exceptionTransformer</emphasis>
      could be a simple POJO that creates error response objects, you could reference
      the "nullChannel" to suppress the errors, or you could leave 'error-channel' out
      to let the Exception propagate.
    </para>
  </section>

  <section id="jms-outbound-gateway">
    <title>Outbound Gateway</title>
    <para>
      The outbound Gateway creates JMS Messages from Spring Integration Messages and then sends to a
      'request-destination'. It will then handle the JMS reply Message either by using a selector to
      receive from the 'reply-destination' that you configure, or if no 'reply-destination' is provided,
      it will create JMS TemporaryQueues. Notice that the "reply-channel" is also provided.
      <programlisting language="xml"><![CDATA[ <jms:outbound-gateway id="jmsOutGateway"
                       request-destination="outQueue"
                       request-channel="outboundJmsRequests"
                       reply-channel="jmsReplies"/>]]></programlisting>
    </para>
    <para>
      The 'outbound-gateway' payload extraction properties are inversely related to those of the
      'inbound-gateway' (see the discussion above). That means that the 'extract-request-payload' property value
      applies to the Spring Integration Message that is being converted into a JMS Message to be
      <emphasis>sent as a request</emphasis>, and the 'extract-reply-payload' property value applies to the
      JMS Message that is <emphasis>received as a reply</emphasis> and then converted into a Spring Integration
      Message to be subsequently sent to the 'reply-channel' as shown in the example configuration above.
    </para>
  </section>
  
  <section id="jms-header-mapping">
  	<title>Mapping Message Headers to/from JMS Message</title>
  
    <para>
    JMS Message can contain meta-information such as  JMS API headers as well as simple properties. 
    You can map those to/from Spring Integration Message Headers using <classname>JmsHeaderMapper</classname>.
    The JMS API headers are passed to the appropriate setter methods (e.g. setJMSReplyTo) whereas other headers will 
    be copied to the general properties of the JMS Message.

    JMS Outbound Gateway is bootstrapped with the default implementation of <classname>JmsHeaderMapper</classname> which will map 
    standard JMS API Headers as well as primitive/String Message Headers. Custom  header mapper could also be
    provided via <code>header-mapper</code> attribute of inbound and outbound gateways.
    </para>
  
  </section>
  
  
   <section id="jms-conversion-and-marshalling">
    <title>Message Conversion, Marshalling and Unmarshalling</title>
    <para>
    	If you need to convert the message, all JMS adapters and gateways, allow you to 
    	provide a <interfacename>MessageConverter</interfacename> via <emphasis>message-converter</emphasis> attribute. Simply provide the
        bean name of an instance of <interfacename>MessageConverter</interfacename> that is available within the same
        ApplicationContext. 
        Also, to provide some consistency with Marshaller and Unmarshaller interfaces Spring provides <interfacename>MarshallingMessageConverter</interfacename>
        which you can configure with your own custom Marshallers and Unmarshallers
    </para>
  <programlisting language="xml"><![CDATA[ <int-jms:inbound-gateway request-destination="requestQueue" 
                             request-channel="inbound-gateway-channel"
                             message-converter="marshallingMessageConverter"/>
                             
 <bean id="marshallingMessageConverter" 
       class="org.springframework.jms.support.converter.MarshallingMessageConverter">
   <constructor-arg>
      <bean class="org.bar.SampleMarshaller"/>
   </constructor-arg>
   <constructor-arg>
      <bean class="org.bar.SampleUnmarshaller"/>
   </constructor-arg>
 </bean>                                              
 ]]></programlisting>   
      
        
     <note>
     Note, however, that when you provide your own MessageConverter instance, it will still
     be wrapped within the HeaderMappingMessageConverter. This means that the 'extract-request-payload'
     and 'extract-reply-payload' properties may affect what actual objects are passed to your converter. The
     HeaderMappingMessageConverter itself simply delegates to a target MessageConverter while also mapping the
     Spring Integration MessageHeaders to JMS Message properties and vice-versa.
     </note>

   </section>

  <section id="jms-channel">
    <title>JMS Backed Message Channels</title>
    <para>
      The Channel Adapters and Gateways featured above are all intended for applications that are integrating
      with other external systems. The inbound options assume that some other system is sending JMS Messages
      to the JMS Destination and the outbound options assume that some other system is receiving from the
      Destination. The other system may or may not be a Spring Integration application. Of course, when sending
      the Spring Integration Message instance as the body of the JMS Message itself (with the 'extract-payload'
      value set to false), it is assumed that the other system is based on Spring Integration. However,
      that is by no means a requirement. That flexibility is one of the benefits of using a Message-based
      integration option with the abstraction of "channels" or Destinations in the case of JMS.
	</para>
    <para>
      There are cases where both the producer and consumer for a given JMS Destination are intended to be
      part of the same application, running within the same process. This could be accomplished by using a
      pair of inbound and outbound Channel Adapters. The problem with that approach is that two adapters are
      required even though conceptually the goal is to have a single Message Channel. A better option is
      supported as of Spring Integration version 2.0. Now it is possible to define a single "channel" when
      using the JMS namespace.
      <programlisting language="xml"><![CDATA[ <jms:channel id="jmsChannel" queue="exampleQueue"/>]]></programlisting>
    </para>
    <para>
      The channel in the above example will behave much like a normal &lt;channel/&gt; element from the main
      Spring Integration namespace. It can be referenced by both "input-channel" and "output-channel" attributes
      of any endpoint. The difference is that this channel is backed by a JMS Queue instance named "exampleQueue".
      This means that asynchronous messaging is possible between the producing and consuming endpoints, but
      unlike the simpler asynchronous Message Channels created by adding a &lt;queue/&gt; sub-element within a
      non-JMS &lt;channel/&gt; element, the Messages are not just stored in an in-memory queue. Instead those
      Messages are passed within a JMS Message body, and the full power of the underlying JMS provider is then
      available for that channel. Probably the most common rationale for using this alternative would be to
      take advantage of the persistence made available by the <emphasis>store and forward</emphasis> approach
      of JMS messaging. If configured properly, the JMS-backed Message Channel also supports transactions.
      In other words, a producer would not actually write to a transactional JMS-backed channel if its send
      operation is part of a transaction that rolls back. Likewise, a consumer would not physically remove a
      JMS Message from the channel if the reception of that Message is part of a transaction that rolls back.
      Note that the producer and consumer transactions are separate in such a scenario. This is significantly
      different than the propagation of a transactional context across the simple, synchronous &lt;channel/&gt;
      element that has no &lt;queue/&gt; sub-element.
    </para>
    <para>
      Since the example above is referencing a JMS Queue instance, it will act as a point-to-point channel. If
      on the other hand, publish/subscribe behavior is needed, then a separate element can be used, and a JMS
      Topic can be referenced instead.
      <programlisting language="xml"><![CDATA[ <jms:publish-subscribe-channel id="jmsChannel" topic="exampleTopic"/>]]></programlisting>
    </para>
    <para>
      For either type of JMS-backed channel, the name of the destination may be provided instead of a reference.
      <programlisting language="xml"><![CDATA[ <jms:channel id="jmsQueueChannel" queue-name="exampleQueueName"/>

 <jms:publish-subscribe-channel id="jmsTopicChannel" topic-name="exampleTopicName"/>]]></programlisting>
    </para>
    <para>
      In the examples above, the Destination names would be resolved by Spring's default
      <classname>DynamicDestinationResolver</classname> implementation, but any implementation of the
      <interfacename>DestinationResolver</interfacename> interface could be provided. Also, the JMS
      <interfacename>ConnectionFactory</interfacename> is a required property of the channel, but by default
      the expected bean name would be "connectionFactory". The example below provides both a custom instance
      for resolution of the JMS Destination names and a different name for the ConnectionFactory.
      <programlisting language="xml"><![CDATA[ <jms:channel id="jmsChannel" queue-name="exampleQueueName"
              destination-resolver="customDestinationResolver"
              connection-factory="customConnectionFactory"/>]]></programlisting>
    </para>
  </section>

  <section id="jms-samples">
    <title>JMS Samples</title>
    <para>
      To experiment with these JMS adapters, check out JMS samples available in our new Samples Git repository
      available here: http://git.springsource.org/+spring-integration/spring-integration/samples . 
      There are two samples included. One provides inbound and outbound Channel Adapters, and the
      other provides inbound and outbound Gateways. They are configured to run with an embedded ActiveMQ process, but
      the "common.xml" file can easily be modified to support either a different JMS provider or a standalone
      ActiveMQ process. In other words, you can split the configuration so that the inbound and outbound adapters are
      running in separate JVMs. If you have ActiveMQ installed, simply modify the "brokerURL" property within the
      configuration to use "tcp://localhost:61616" for example (instead of "vm://localhost"). Both of the samples
      accept input via stdin and then echo back to stdout. Look at the configuration to see how these messages are
      routed over JMS.
    </para>
  </section>

</chapter>
