Specifying the MDB JMS Provider

The responsibilities of the ASF domains are well defined by the JMS specification, so we won't go into a discussion of how the ASF components are implemented. Rather, we'll discuss how ASF components used by the JBoss MDB layer are integrated, using MBeans that allow either the application server interfaces or the JMS provider interfaces to be replaced with alternate implementations.

Let's start with the org.jboss.jms.jndi.JMSProviderLoader MBean. This MBean is responsible for loading an instance of the org.jboss.jms.jndi.JMSProviderAdaptor interface into the JBoss server and binding it into JNDI. The JMSProviderAdaptor interface is an abstraction that defines how to get the root JNDI context for the JMS provider, and an interface for getting and setting the JNDI names for the Context.PROVIDER_URL for the root InitialContext, and the QueueConnectionFactory and TopicConnectionFactory locations in the root context.

This is all that is really necessary to bootstrap use of a JMS provider. By abstracting this information into an interface, you can use alternate JMS ASF provider implementations with the JBoss MDB container. org.jboss.jms.jndi.JBossMQProvider is the default implementation of the JMSProviderAdaptor interface, and it provides the adaptor for the JBossMQ JMS provider. To replace the JBossMQ provider with an alternate JMS ASF implementation, you simply create an implementation of the JMSProviderAdaptor interface and configure the JMSProviderLoader with the classname of the implementation. You'll see an example of this later in this chapter.

In addition to being able to replace the JMS provider used for MDBs, you can also replace the javax.jms.ServerSessionPool interface implementation. This is possible by configuring the classname of the org.jboss.jms.asf.ServerSessionPoolFactory implementation, using the org.jboss.jms.asf.ServerSessionPoolLoader MBean PoolFactoryClass attribute. The default ServerSessionPoolFactory factory implementation is the JBoss org.jboss.jms.asf.StdServerSessionPoolFactory class.

The org.jboss.jms.jndi.JMSProviderLoader MBean

The JMSProviderLoader MBean service creates a JMS provider adaptor and binds it into JNDI. A JMS provider adaptor is a class that implements the org.jboss.jms.jndi.JMSProviderAdaptor interface. It is used by the MDB container to access a JMS service provider in a provider-independent manner. The configurable attributes of the JMSProviderLoader service are as follows:

• ProviderName A unique name for the JMS provider. This will be used to bind the JMSProviderAdaptor instance into JNDI under java :/<ProviderName> unless it is overridden by the AdapterJNDIName attribute.

• ProviderAdapterClass The fully qualified classname of the org.jboss.jms.jndi.JMSProviderAdaptor interface to create an instance of. To use an alternate JMS provider, such as SonicMQ, you create an implementation of the JMSProviderAdaptor interface that allows the administration of the InitialContext provider URL, and the locations of the QueueConnectionFactory and TopicConnectionFactory in JNDI.

• AdapterJNDIName The exact JNDI name under which the JMSProviderAdaptor instance will be bound.

• ProviderURL The JNDI Context.PROVIDER_URL value to use when creating the JMS provider root InitialContext.

• QueueFactoryRef The JNDI name under which the provider javax.jms.QueueConnectionFactory will be bound.

• TopicFactoryRef The JNDI name under which the javax.jms.TopicConnectionFactory will be bound.

Listing 6.13 shows a JMSProviderLoader for accessing a remote JBossMQ server.

Listing 6.13. A JMSProviderLoader for Accessing a Remote JBossMQ Server

<mbean code="org.jboss.jms.jndi.JMSProviderLoader"
       name="jboss.mq:service=JMSProviderLoader,name=RemoteJBossMQProvider">
    <attribute name="ProviderName">RemoteJMSProvider</attribute>
    <attribute name="ProviderUrl">jnp://remotehost:1099</attribute>
    <attribute name="ProviderAdapterClass">
        org.jboss.jms.jndi.JBossMQProvider
    </attribute>
    <attribute name="QueueFactoryRef">XAConnectionFactory</attribute>
    <attribute name="TopicFactoryRef">XAConnectionFactory</attribute>
</mbean>

The RemoteJMSProvider can be referenced on the MDB invoker config, as shown in the jboss.xml fragment in Listing 6.14.

Listing 6.14. A jboss.xml Fragment for Specifying the MDB JMSProviderAdapter

<proxy-factory-config>
    <JMSProviderAdaptorJNDI>RemoteJMSProvider</JMSProviderAdaptorJNDI>
    <ServerSessionPoolFactoryJNDI>StdJMSPool</ServerSessionPoolFactoryJNDI>
    <MaximumSize>15</MaximumSize>
    <MaxMessages>1</MaxMessages>
    <MDBConfig>
        <ReconnectIntervalSec>10</ReconnectIntervalSec>
        <DLQConfig>
            <DestinationQueue>queue/DLQ</DestinationQueue>
            <MaxTimesRedelivered>10</MaxTimesRedelivered>
            <TimeToLive>0</TimeToLive>
        </DLQConfig>
    </MDBConfig>
</proxy-factory-config>

Incidentally, being able to specify multiple invoker-proxy-binding elements allows an MDB to listen to the same queue/topic on multiple servers because you can configure multiple bindings with different JMSProviderAdaptorJNDI settings. Alternatively, you can integrate the JMS provider by using a JCA configuration like the one shown in Listing 6.15.

Listing 6.15. A jms-ds.xml Descriptor for Integrating a JMSProviderAdapter via JCA

<tx-connection-factory>
    <jndi-name>RemoteJmsXA</jndi-name>
    <xa-transaction/>
    <adapter-display-name>JMS Adapter</adapter-display-name>
    <config-property name="JMSProviderAdaptorJNDI"
                     type="java.lang.String">RemoteJMSProvider</config-property>
    <config-property name="SessionDefaultType"
                     type="java.lang.String">javax.jms.Topic</config-property>

    <security-domain-and-application>JmsXARealm</security-domain-and-application>
</tx-connection-factory>

The org.jboss.jms.asf.ServerSessionPoolLoader MBean

The ServerSessionPoolLoader MBean manages a factory for javax.jms.ServerSessionPool objects used by the MDB container. The configurable attributes of the ServerSessionPoolLoader service are as follows:

• PoolName A unique name for the session pool. This will be used to bind the ServerSessionPoolFactory instance into JNDI under java:/PoolName.

• PoolFactoryClass The fully qualified classname of the org.jboss.jms.asf.ServerSessionPoolFactory interface to create an instance of.

• XidFactory The JMX ObjectName of the service to use for generating javax.transaction.xa.Xid values for local transactions when a two-phase commit is not required. The XidFactory MBean must provide an Instance operation that returns a org.jboss.tm.XidFactoryMBean instance.

Integrating Non-JBoss JMS Providers

As mentioned previously in this chapter, you can replace the JBossMQ JMS implementation with a foreign implementation. You can take a variety of approaches to doing the replacement:

• Change the JMSProviderLoader from the JBossMQProvider class to one that instantiates the correct JNDI context for communicating with the foreign JMS provider's managed objects.

• Use the ExternalContext MBean to federate the foreign JMS provider's managed objects into the JBoss JNDI tree.

• Use MBeans to instantiate the foreign JMS objects into the JBoss JNDI tree. An example of this approach can be found for Websphere MQ at http://sourceforge.net/tracker/index.php?func=detail&aid=753022&group_id=22866&atid=376687.