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Sun Java System Application Server Enterprise Edition 8.2 Developer's Guide

Chapter 13 Using the Java Naming and Directory Interface

A naming service maintains a set of bindings, which relate names to objects. The J2EETM naming service is based on the Java Naming and Directory InterfaceTM (JNDI) API. The JNDI API allows application components and clients to look up distributed resources, services, and EJBTM components. For general information about the JNDI API, see http://java.sun.com/products/jndi/.

You can also see the JNDI tutorial at http://java.sun.com/products/jndi/tutorial/.

This chapter contains the following sections:

Accessing the Naming Context

The Application Server provides a naming environment, or context, which is compliant with standard J2EE 1.4 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 J2EE 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:

Note –

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.

Naming Environment for J2EE Application Components

The namespace for objects looked up in a J2EE environment is organized into different subcontexts, with the standard prefix java:comp/env.

The following table describes standard JNDI subcontexts for connection factories in the Application Server.

Table 13–1 Standard JNDI Subcontexts for Connection Factories

Resource Manager  

Connection Factory Type  

JNDI Subcontext  

JDBCTM

javax.sql.DataSource

java:comp/env/jdbc

Transaction Service

javax.transaction.UserTransaction

java:comp/UserTransaction

JMS

javax.jms.TopicConnectionFactory

javax.jms.QueueConnectionFactory

java:comp/env/jms

JavaMailTM

javax.mail.Session

java:comp/env/mail

URL

java.net.URL

java:comp/env/url

Connector

javax.resource.cci.ConnectionFactory

java:comp/env/eis

Accessing EJB Components Using the CosNaming Naming Context

The preferred way of accessing the naming service, even in code that runs outside of a J2EE 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 these properties in the client JVM when accessing EJB components:

-Djavax.rmi.CORBA.UtilClass=com.sun.corba.ee.impl.javax.rmi.CORBA.Util
-Dorg.omg.CORBA.ORBClass=com.sun.corba.ee.impl.orb.ORBImpl
-Dorg.omg.CORBA.ORBSingletonClass=com.sun.corba.ee.impl.orb.ORBSingleton
-Djava.naming.factory.initial=com.sun.jndi.cosnaming.CNCtxFactory

Accessing EJB Components in a Remote Application Server

The recommended approach for looking up an EJB component in a remote Application 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 Application 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 J2EE 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 Application Server deployment descriptor file instead of 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 J2EE 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 Java-based tasks 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 10, 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.

Configuring Resources

The Application Server exposes the following special resources in the naming environment. Full administration details are provided in the following sections:

External JNDI Resources

An external JNDI resource defines custom JNDI contexts and implements the javax.naming.spi.InitialContextFactory interface. There is no specific JNDI parent context for external JNDI resources, except for the standard java:comp/env/.

Create an external JNDI resource in one of these ways:

Custom Resources

A custom resource specifies a custom server-wide resource object factory that implements the javax.naming.spi.ObjectFactory interface. There is no specific JNDI parent context for external JNDI resources, except for the standard java:comp/env/.

Create a custom resource in one of these ways:

Mapping References

The following XML elements map JNDI names configured in the Application Server to resource references in application client, EJB, and web application components:

JNDI names for EJB components must be unique. For example, appending the application name and the module name to the EJB name is one way to guarantee unique names. In this case, mycompany.pkging.pkgingEJB.MyEJB would be the JNDI name for an EJB in the module pkgingEJB.jar, which is packaged in the pkging.ear application.

These elements are part of the sun-web-app.xml, sun-ejb-ref.xml, and sun-application-client.xml deployment descriptor files. For more information about how these elements behave in each of the deployment descriptor files, see Appendix A, Deployment Descriptor Files.

The rest of this section uses an example of a JDBC resource lookup to describe how to reference resource factories. The same principle is applicable to all resources (such as JMS destinations, JavaMail sessions, and so on).

The resource-ref element in the sun-web-app.xml deployment descriptor file maps the JNDI name of a resource reference to the resource-ref element in the web-app.xml J2EE deployment descriptor file.

The resource lookup in the application code looks like this:

InitialContext ic = new InitialContext();
String dsName = "java:comp/env/jdbc/HelloDbDs";
DataSource ds = (javax.sql.DataSource)ic.lookup(dsName);
Connection connection = ds.getConnection();

The resource being queried is listed in the res-ref-name element of the web.xml file as follows:

<resource-ref>
   <description>DataSource Reference</description>
   <res-ref-name>jdbc/HelloDbDs</res-ref-name>
   <res-type>javax.sql.DataSource</res-type>
   <res-auth>Container</res-auth>
</resource-ref>

The resource-ref section in a Application Server specific deployment descriptor, for example sun-web.xml, maps the res-ref-name (the name being queried in the application code) to the JNDI name of the JDBC resource. The JNDI name is the same as the name of the JDBC resource as defined in the resource file when the resource is created.

<resource-ref>
   <res-ref-name>jdbc/HelloDbDs</res-ref-name>
   <jndi-name>jdbc/HelloDbDataSource</jndi-name>
</resource-ref>

The JNDI name in the Application Server specific deployment descriptor must match the JNDI name you assigned to the resource when you created and configured it.