JNDI Naming

In a distributed application, components need to access other components and resources such as databases. For example, a servlet might invoke remote methods on an enterprise bean that retrieves information from a database. In the J2EE platform, the Java Naming and Directory Interface (JNDI) naming service enables components to locate other components and resources. To locate a JDBC resource, for example, an enterprise bean invokes the JNDI lookup method. The JNDI naming service maintains a set of bindings that relate names to objects. The lookup method passes a JNDI name parameter and returns the related object.

JNDI provides a naming context, which is a a set of name-to-object bindings. All naming operations are relative to a context. A name that is bound within a context is the JNDI name of the object. In Specifying a Resource Reference, for example, the JNDI name for the JDBC resource (or data source) is jdbc/ejbTutorialDB. A Context object provides the methods for binding names to objects, unbinding names from objects, renaming objects, and listing the bindings. JNDI 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.

Table 31-1 describes JNDI subcontexts for connection factories in the Sun Java System Application Server Platform Edition 8.

Table 31-1 JNDI Subcontexts for Connection Factories
Resource Manager Type	Connection Factory Type	JNDI Subcontext
JDBC	`javax.sql.DataSource`	`java:comp/env/jdbc`
JMS	`javax.jms.TopicConnectionFactory` `javax.jms.QueueConnectionFactory`	`java:comp/env/jms`
JavaMail	`javax.mail.Session`	`java:comp/env/mail`
URL	`java.net.URL`	`java:comp/env/url`
Connector	`javax.resource.cci.ConnectionFactory`	`java:comp/env/eis`
JAXR Resource Adapter	`javax.xml.registry.ConnectionFactory`	`java:comp/env/eis/JAXR`

Note: To avoid collisions with names of other enterprise resources in the JNDI namespace, and to avoid portability problems, all names in a J2EE application should begin with the string java:comp/env.