Accessing the Naming Context

The Enterprise Server provides a naming environment, or context, which is compliant with standard Java EE requirements. A Context object provides the methods for binding names to objects, unbinding names from objects, renaming objects, and listing the bindings. The InitialContext is the handle to the Java EE naming service that application components and clients use for lookups.

The JNDI API also provides subcontext functionality. Much like a directory in a file system, a subcontext is a context within a context. This hierarchical structure permits better organization of information. For naming services that support subcontexts, the Context class also provides methods for creating and destroying subcontexts.

The rest of this section covers these topics:

• Global JNDI Names

• Accessing EJB Components Using the CosNaming Naming Context

• Accessing EJB Components in a Remote Application Server

• Naming Environment for Lifecycle Modules

Each resource within a server instance must have a unique name. However, two resources in different server instances or different domains can have the same name.

Global JNDI Names

Global JNDI names are assigned according to the following precedence rules:

1. A global JNDI name assigned in the sun-ejb-jar.xml, sun-web.xml, or sun-application-client.xml deployment descriptor file has the highest precedence. See Mapping References.

2. A global JNDI name assigned in a mapped-name element in the ejb-jar.xml, web.xml, or application-client.xml deployment descriptor file has the second highest precedence. The following elements have mapped-name subelements: resource-ref, resource-env-ref, ejb-ref, message-destination, message-destination-ref, session, message-driven, and entity.

3. A global JNDI name assigned in a mappedName attribute of an annotation has the third highest precedence. The following annotations have mappedName attributes: @javax.annotation.Resource, @javax.ejb.EJB, @javax.ejb.Stateless, @javax.ejb.Stateful, and @javax.ejb.MessageDriven.

4. A default global JNDI name is assigned in some cases if no name is assigned in deployment descriptors or annotations.

   • For an EJB 2.x dependency or a session or entity bean with a remote interface, the default is the fully qualified name of the home interface.

   • For an EJB 3.0 dependency or a session bean with a remote interface, the default is the fully qualified name of the remote business interface.

   • If both EJB 2.x and EJB 3.0 remote interfaces are specified, or if more than one 3.0 remote interface is specified, there is no default, and the global JNDI name must be specified.

   • For all other component dependencies that must be mapped to global JNDI names, the default is the name of the dependency relative to java:comp/env. For example, in the @Resource(name="jdbc/Foo") DataSource ds; annotation, the global JNDI name is jdbc/Foo.

Accessing EJB Components Using the CosNaming Naming Context

The preferred way of accessing the naming service, even in code that runs outside of a Java EE container, is to use the no-argument InitialContext constructor. However, if EJB client code explicitly instantiates an InitialContext that points to the CosNaming naming service, it is necessary to set the java.naming.factory.initial property to com.sun.jndi.cosnaming.CNCtxFactory in the client JVM when accessing EJB components. You can set this property as a command-line argument, as follows:

-Djava.naming.factory.initial=com.sun.jndi.cosnaming.CNCtxFactory

Or you can set this property in the code, as follows:

Properties properties = null;
      try {
            properties = new Properties();
            properties.put("java.naming.factory.initial",
                  "com.sun.jndi.cosnaming.CNCtxFactory");
      ...

The java.naming.factory.initial property applies to only one instance; it is not cluster-aware.

Accessing EJB Components in a Remote Application Server

The recommended approach for looking up an EJB component in a remote Enterprise Server from a client that is a servlet or EJB component is to use the Interoperable Naming Service syntax. Host and port information is prepended to any global JNDI names and is automatically resolved during the lookup. The syntax for an interoperable global name is as follows:

corbaname:iiop:host:port#a/b/name

This makes the programming model for accessing EJB components in another Enterprise Server exactly the same as accessing them in the same server. The deployer can change the way the EJB components are physically distributed without having to change the code.

For Java EE components, the code still performs a java:comp/env lookup on an EJB reference. The only difference is that the deployer maps the ejb-reference element to an interoperable name in an Enterprise Server deployment descriptor file instead of to a simple global JNDI name.

For example, suppose a servlet looks up an EJB reference using java:comp/env/ejb/Foo, and the target EJB component has a global JNDI name of a/b/Foo.

The ejb-ref element in sun-web.xml looks like this:

<ejb-ref>
   <ejb-ref-name>ejb/Foo</ejb-ref-name>
   <jndi-name>corbaname:iiop:host:port#a/b/Foo</jndi-name>
<ejb-ref>

The code looks like this:

Context ic = new InitialContext();
Object o = ic.lookup("java:comp/env/ejb/Foo");

For a client that doesn’t run within a Java EE container, the code just uses the interoperable global name instead of the simple global JNDI name. For example:

Context ic = new InitialContext();
Object o = ic.lookup("corbaname:iiop:host:port#a/b/Foo");

Objects stored in the interoperable naming context and component-specific (java:comp/env) naming contexts are transient. On each server startup or application reloading, all relevant objects are re-bound to the namespace.

Naming Environment for Lifecycle Modules

Lifecycle listener modules provide a means of running short or long duration tasks based on Java technology within the application server environment, such as instantiation of singletons or RMI servers. These modules are automatically initiated at server startup and are notified at various phases of the server life cycle. For details about lifecycle modules, see Chapter 13, Developing Lifecycle Listeners.

The configured properties for a lifecycle module are passed as properties during server initialization (the INIT_EVENT). The initial JNDI naming context is not available until server initialization is complete. A lifecycle module can get the InitialContext for lookups using the method LifecycleEventContext.getInitialContext() during, and only during, the STARTUP_EVENT, READY_EVENT, or SHUTDOWN_EVENT server life cycle events.