JMS

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The Java Message Service (JMS) is Message Oriented Middleware (MOM) designed to send messages between cooperating processes on different computers.

NetKernel provides a transport that adapts the JMS API and hides many of the complexities. However, because MOM products do not follow uniform standards the JMS system cannot fully abstract MOM for Java and each use of a vendor's product will require some customization. The design of this library has been to provide a standard base which should be relatively easy to customize to a specific enterprise JMS configuration. Out of the box it provides the following functionality:

Send and receive from Queues
Publish and subscribe to Topics
Support for TextMessage and BytesMessage
Flexible JNDI InitialContext configuration
Full setting and getting of message properties and JMS headers via NVP
Dynamic configuration changes
Connection to multiple queues and topics concurrently
Message Acknowledgment based on NetKernel service response, i.e. failure means no ack

Please contact us for expert help in adapting your messaging vendor's system to NetKernel's JMS transport.

Architecture

The JMS module has two parts - a message driven transport which, when it receives a message, will issue the message as a NetKernel root request into the host fulcrum module's local address space A client accessor which can explicitly send messages to a queue or topic. In addition, the JMS module provides a JMS Message Broker connection aspect and a transreptor to create a connection aspect from an XML configuration - the configuration is dynamically polled which means the JMS environment can be dynamically updated with no down time.

Typically NetKernel will be configured to host message-driven-services which will be invoked by the JMS Transport. These services may then issue further messages to other queues or topics. However the choice of architecture will depend on the application - it would be equally as easy to have NetKernel as the primary driver of a message queue - generating JMS messages based upon some other transport-initiated-event such as a Web-application form submission or a SOAP or email message event occurring on another transport.

Configuration

A host fulcrum module should be created to host the JMS module and must provide an XML configuration and the actual mapped services which can handle the message requests generated by the JMS transport.

The configuration must be located at ffcpl:/etc/JMSConfig.xml. A single XML configuration resource is used to configure both the JMS producer accessor and JMS consumer transport. Here is a commented example:

<JMSProducer>
  <!-- a list of name value pairs to put into the InitialContext of JNDI -->
  <jndiContext>
    <java.naming.factory.initial>
      org.codehaus.activemq.jndi.ActiveMQInitialContextFactory
    </java.naming.factory.initial>
    <java.naming.provider.url>tcp://localhost:61616</java.naming.provider.url>
    <queue.MyQueue>example.MyQueue</queue.MyQueue>
    <topic.MyTopic>example.MyTopic</topic.MyTopic>
  </jndiContext>
  <!-- JNDI name of connection factory for Queues -->
  <queueConnectionFactory>QueueConnectionFactory</queueConnectionFactory>
  <!-- JNDI name of connection factory for Topics -->
  <topicConnectionFactory>TopicConnectionFactory</topicConnectionFactory>
  <!-- a set of queue and topic declarations -->
  <!-- a queue declaration -->
  <queue>
    <!-- logical JNDI name of Queue -->
    <name>MyQueue</name>
    <!-- BytesMessage and TextMessage are supported (only used by producer) -->
    <messageType>BytesMessage</messageType>
    <!--
      if true and acknowledgement is always given,
      if false only when no exception (only used by consumer)
     -->
    <ackOnException>false</ackOnException>
  </queue>
  <!-- a topic declaration -->
  <topic>
    <!-- logical JNDI name of Topic -->
    <name>MyTopic</name>
    <messageType>BytesMessage</messageType>
    <ackOnException>false</ackOnException>
    <!-- an optional standard message selector string -->
    <messageSelector>ContentType = 'content/unknown'</messageSelector>
  </topic>
</JMSProducer>