JMS Transactions

In addition to the transaction mediator, WSO2 ESB also supports JMS transactions. 

The JMS transport shipped with WSO2 ESB supports both local and distributed JMS transactions. You can use local transactions to group messages received in a JMS queue. Local transactions are not supported for messages sent to a JMS queue.

This section describes:

• JMS Local Transactions
• JMS Distributed Transactions

JMS local transactions 

A local transaction represents a unit of work on a single connection to a data source managed by a resource manager. In JMS, you can use the JMS API to get a transacted session and to call methods for commit or roll back for the relevant transaction objects. This is managed internally by a resource manager. There is no external transaction manager involved in the coordination of such transactions.

Let's explore a a sample scenario that demonstrates how to handle a transaction using JMS in a situation where the back-end service is unreachable.

Sample scenario

A message is read from a JMS queue and is processed by a back-end service. In the successful scenario, the transaction will be committed and the request will be sent to the back end service. In the failure scenario, while executing a sequence, a failure occurs and the ESB receives a fault. This cause the JMS transaction to roll back.

The sample scenario can be depicted as follows:

Prerequisites

• Windows, Linux or Solaris operating systems with WSO2 ESB installed. For instructions on downloading and installing WSO2 ESB, see Getting Started with WSO2 ESB.
• WSO2 Message Broker installed. For instructions on downloading and installing WSO2 Message Broker, see Getting Started with WSO2 Message Broker.
• WSO2 ESB's JMS transport configured with WSO2 Message Broker. For instructions on configuring WSO2 ESB's JMS transport with WSO2 Message Broker, see Configure with WSO2 Message Broker.

Configuring the sample scenario

1. Configure the JMS local transaction by defining the following parameter in the <ESB HOME>/repository/conf/axis2/axis2.xml file. By default the session is not transacted. In order to make it transacted, set the parameter to true.

   <parameter name="transport.jms.SessionTransacted">true</parameter>

   Once done, the JMS listener configuration for WSO2 MB in the axis2.xml file should be as follows:

   <transportReceiver name="jms" class="org.apache.axis2.transport.jms.JMSListener">
          <parameter name="myTopicConnectionFactory" locked="false">
               <parameter name="java.naming.factory.initial" locked="false">org.wso2.andes.jndi.PropertiesFileInitialContextFactory</parameter>
               <parameter name="java.naming.provider.url" locked="false">repository/conf/jndi.properties</parameter>
               <parameter name="transport.jms.ConnectionFactoryJNDIName" locked="false">TopicConnectionFactory</parameter>
           	<parameter name="transport.jms.ConnectionFactoryType" locked="false">topic</parameter>
           	<parameter name="transport.jms.SessionTransacted">true</parameter>
          </parameter>
    
          <parameter name="myQueueConnectionFactory" locked="false">
              	<parameter name="java.naming.factory.initial" locked="false">org.wso2.andes.jndi.PropertiesFileInitialContextFactory</parameter>
              	<parameter name="java.naming.provider.url" locked="false">repository/conf/jndi.properties</parameter>
              	<parameter name="transport.jms.ConnectionFactoryJNDIName" locked="false">QueueConnectionFactory</parameter>
           	<parameter name="transport.jms.ConnectionFactoryType" locked="false">queue</parameter>
           	<parameter name="transport.jms.SessionTransacted">true</parameter>	
   	   </parameter>
    
          <parameter name="default" locked="false">
              	<parameter name="java.naming.factory.initial" locked="false">org.wso2.andes.jndi.PropertiesFileInitialContextFactory</parameter>
              	<parameter name="java.naming.provider.url" locked="false">repository/conf/jndi.properties</parameter>
              	<parameter name="transport.jms.ConnectionFactoryJNDIName" locked="false">QueueConnectionFactory</parameter>
           	<parameter name="transport.jms.ConnectionFactoryType" locked="false">queue</parameter>
           	<parameter name="transport.jms.SessionTransacted">true</parameter>
   		</parameter>
      </transportReceiver>

2. Copy and paste the following configuration into the Synapse configuration in $ESB_HOME/repository/deployment/server/synapse-configs/<node>/synapse.xml.

   <definitions xmlns="http://ws.apache.org/ns/synapse">
      <proxy name="StockQuoteProxy" transports="jms" startOnLoad="true">
         <target>
            <inSequence>
               <property name="OUT_ONLY" value="true"/>
               <callout serviceURL="http://localhost:9000/services/SimpleStockQuoteService">
                  <source type="envelope"/>
                  <target key="placeOrder"/>
               </callout>
               <log level="custom">
                  <property name="Transaction Action" value="Committed"/>
               </log>
            </inSequence>
            <faultSequence>
               <property name="SET_ROLLBACK_ONLY" value="true" scope="axis2"/>
               <log level="custom">
                  <property name="Transaction Action" value="Rollbacked"/>
               </log>
            </faultSequence>
         </target>
         <parameter name="transport.jms.ContentType">
            <rules>
               <jmsProperty>contentType</jmsProperty>
               <default>application/xml</default>
            </rules>
         </parameter>
      </proxy>
      <sequence name="fault">
         <log level="full">
            <property name="MESSAGE" value="Executing default &#34;fault&#34; sequence"/>
            <property name="ERROR_CODE" expression="get-property('ERROR_CODE')"/>
            <property name="ERROR_MESSAGE" expression="get-property('ERROR_MESSAGE')"/>
         </log>
         <drop/>
      </sequence>
      <sequence name="main">
         <log/>
         <drop/>
      </sequence>
   </definitions>

   According to the above configuration, a message will be read from the JMS queue and will be sent to the SimpleStockQuoteService running on the Axis2 back-end server. If a failure occurs, the transaction will roll back. 

   In the above configuration, the following property is set to true in the fault handler, in order to roll back the transaction when a failure occurs. 

   <property name="SET_ROLLBACK_ONLY" value="true" scope="axis2"/>

3. Deploy the back-end service SimpleStockQuoteService . For instructions on deploying sample back-end services, see Deploying sample back-end services.

4. Start the Axis2 server. For instructions on starting the Axis2 server, see Starting the Axis2 server.

   You now have a running ESB instance, WSO2 Message Broker instance and a sample back-end service to simulate the sample scenario. Now let's execute the JMS client.

   Due to the asynchronous behavior of the Send Mediator, you cannot you use it with a http/https endpoint, but you can use it in asynchronous use cases, for example with another JMS as endpoint.

Executing the sample scenario

To execute the JMS client

• Run the following command from the <ESB_HOME>/samples/axis2Client directory. 

  ant jmsclient -Djms_type=pox -Djms_dest=dynamicQueues/StockQuoteProxy -Djms_payload=MSFT

  This will trigger a sample message to the JMS Server.

Testing the sample scenario

Successful scenario

In order to simulate the successful scenario, the message should mediate successfully.

When the message mediates successfully, the output on the Axis2 server start-up console will be as follows:

The ESB debug log will display an INFO message as follows, indicating that the transaction is committed. 

Failure Scenario

In order to simulate the failure scenario, you need to stop the sample Axis2 Server and execute the JMS client once again. 
In this scenario, the ESB debug log will display an INFO message as follows, indicating that the transaction is rolled back.

JMS distributed transactions 

The WSO2 ESB also supports distributed JMS transactions. You can use the JMS transport with more than one distributed resource, for example, two remote database servers. An external transaction manager coordinates the transaction. Designing and using JMS distributed transactions is more complex than using local JMS transactions.

The transaction mediator can be used to mark a distributed transaction, which involves a distributed transaction that spans through multiple resources. The transaction manager is the primary component of the distributed transaction support infrastructure. However, the JDBC driver and the application server where you deploy the applications should have the following two characteristics:

• The driver should implement the JDBC 2.0 API (including the optional package interfaces XADataSource and XAConnection) or higher, and the JTA interface XAResource.
• The application server should provide a Datasource class that is implemented to interact with the distributed transaction infrastructure and a connection pooling model for performance improvements.

When JMS transactions are in place, local transactions are managed by the JMS provider itself, whereas the distributed JMS transactions are managed by the XAResource enabled transaction manager in the Java EE application server.