Resources and JNDI Naming

Resources and JNDI Naming

In a distributed application, components need to access other components and resources suchas databases. For example, a servlet might invoke remote methods on an enterprisebean that retrieves information from a database. In the Java EE platform, theJava Naming and Directory Interface (JNDI) naming service enables components to locate other componentsand resources.

A resource is a program object that provides connections to systems, such asdatabase servers and messaging systems. (A JDBC resource is sometimes referred to asa data source.) Each resource object is identified by a unique, people-friendly name,called the JNDI name.

For example, the JNDI name of the JDBC resource for the JavaDB database that is shipped with the Application Server isjdbc/__default.

An administrator creates resources in a JNDI namespace. In the Application Server, youcan use either the Admin Console or theasadmin command to create resources.Applications then use annotations to inject the resources. If an application uses resourceinjection, the Application Server invokes the JNDI API, and the application is notrequired to do so. However, it is also possible for an application tolocate resources by making direct calls to the JNDI API.

A resource object and its JNDI name are bound together by thenaming and directory service. To create a new resource, a new name-object binding isentered into the JNDI namespace.

For information on creating Java Message Service (JMS) resources, seeCreating JMS Administered Objects for the Synchronous Receive Example. For anexample of creating a JDBC resource, seeCreating a Data Source in the Application Server.

You inject resources by using the@Resource annotation in an application. For informationon resource injection, see the following sections of this Tutorial:

• Declaring Resource References

• Updating Data in the Database, for information on injecting aUserTransaction resource

• JMS Connection Factories,JMS Destinations, andUsing@Resource Annotations in Java EE Components, for information on injecting JMS resources

You can use a deployment descriptor to override the resource mapping that youspecify in an annotation. Using a deployment descriptor allows you to change anapplication by repackaging it, rather than by both recompiling the source files andrepackaging. However, for most applications, a deployment descriptor is not necessary.

Copyright © 2010, Oracle and/or its affiliates. All rights reserved.Legal Notices