Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Administration Guide

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# About Java Naming and Directory Interface (JNDI)

This section discusses the Java Naming and Directory Interface (JNDI). JNDI is an application programming interface (API) for accessing different kinds of naming and directory services. J2EE components locate objects by invoking the JNDI lookup method.

This section covers the following topics:

- JNDI Names and Resources

- J2EE Naming Services

- Naming References and Binding Information

## JNDI Names and Resources

JNDI is the acronym for the Java Naming and Directory Interface API. By making calls to this API, applications locate resources and other program objects. A resource is a program object that provides connections to systems, such as database servers and messaging systems. (A JDBC resource is sometimes referred to as a data source.) Each resource object is identified by a unique, people-friendly name, called the JNDI name. A resource object and its JNDI name are bound together by the naming and directory service, which is included with the Application Server. To create a new resource, a new name-object binding is entered into the JNDI.

## J2EE Naming Services

A JNDI name is a people-friendly name for an object. These names are bound to their objects by the naming and directory service that is provided by a J2EE server. Because J2EE components access this service through the JNDI API, the object usually uses its JNDI name. For example, the JNDI name of the PointBase database is `jdbc/Pointbase`. When it starts up, the Application Server reads information from the configuration file and automatically adds JNDI database names to the name space.

J2EE application clients, enterprise beans, and web components are required to have access to a JNDI naming environment.

The application component's naming environment is a mechanism that allows customization of the application component's business logic during deployment or assembly. Use of the application component's environment allows the application component to be customized without the need to access or change the application component's source code.

A J2EE container implements the application component's environment, and provides it to the application component instance as a JNDI naming context. The application component's environment is used as follows:

- The application component's business methods access the environment using the JNDI interfaces. The application component provider declares in the deployment descriptor all the environment entries that the application component expects to be provided in its environment at runtime.

- The container provides an implementation of the JNDI naming context that stores the application component environment. The container also provides the tools that allow the deployer to create and manage the environment of each application component.

- A deployer uses the tools provided by the container to initialize the environment entries that are declared in the application component's deployment descriptor. The deployer sets and modifies the values of the environment entries.

- The container makes the environment naming context available to the application component instances at runtime. The application component's instances use the JNDI interfaces to obtain the values of the environment entries.

Each application component defines its own set of environment entries. All instances of an application component within the same container share the same environment entries. Application component instances are not allowed to modify the environment at runtime.

## Naming References and Binding Information

A resource reference is an element in a deployment descriptor that identifies the component’s coded name for the resource. More specifically, the coded name references a connection factory for the resource. In the example given in the following section, the resource reference name is `jdbc/SavingsAccountDB`.

The JNDI name of a resource and the name of the resource reference are not the same. This approach to naming requires that you map the two names before deployment, but it also decouples components from resources. Because of this de-coupling, if at a later time the component needs to access a different resource, the name does not need to change. This flexibility also makes it easier for you to assemble J2EE applications from preexisting components.

The following table lists JNDI lookups and their associated references for the J2EE resources used by the Application Server.

Table 6–1 JNDI Lookups and Their Associated References

JNDI Lookup Name | Associated Reference
--- | ---
`java:comp/env` | Application environment entries
`java:comp/env/jdbc` | JDBC DataSource resource manager connection factories
`java:comp/env/ejb` | EJB References
`java:comp/UserTransaction` | UserTransaction references
`java:comp/env/mail` | JavaMail Session Connection Factories
`java:comp/env/url` | URL Connection Factories
`java:comp/env/jms` | JMS Connection Factories and Destinations
`java:comp/ORB` | ORB instance shared across application components

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