Circumventing Class Loader Isolation

Since each application or individually deployed module class loader universe is isolated, an application or module cannot load classes from another application or module. This prevents two similarly named classes in different applications from interfering with each other.

To circumvent this limitation for libraries, utility classes, or individually deployed modules accessed by more than one application, you can include the relevant path to the required classes in one of these ways:

• Using the System Class Loader

• Using the Common Class Loader

• Sharing Libraries Across a Cluster

• Packaging the Client JAR for One Application in Another Application

Using the System class loader or Common class loader requires a server restart and makes a library accessible to all applications or modules deployed on servers that share the same configuration.

Using the System Class Loader

To use the System class loader, do one of the following, then restart the server:

• Use the Admin Console. In the developer profile, select the Enterprise Server component and select the JVM Settings tab. In the cluster profile, select the JVM Settings component under the relevant configuration. Then select the Path Settings tab and edit the System Classpath field. For details, click the Help button in the Admin Console.

• Edit the system-classpath attribute of the java-config element in the domain.xml file. For details about domain.xml, see the Sun GlassFish Enterprise Server v2.1.1 Administration Reference.

Using the System class loader makes an application or module accessible to all applications or modules deployed on servers that share the same configuration.

Add the classes to the system-classpath attribute of the DAS in addition to the system-classpath attribute on the server instances that use the classes. The default name for the DAS configuration is server-config.

Using the Common Class Loader

To use the Common class loader, copy the JAR files into the domain-dir/lib directory or copy the .class files into the domain-dir/lib/classes directory, then restart the server.

Using the Common class loader makes an application or module accessible to all applications or modules deployed on servers that share the same configuration.

For example, using the Common class loader is the recommended way of adding JDBC drivers to the Enterprise Server. For a list of the JDBC drivers currently supported by the Enterprise Server, see the Sun GlassFish Enterprise Server v2.1.1 Release Notes. For configurations of supported and other drivers, see Configurations for Specific JDBC Drivers in Sun GlassFish Enterprise Server v2.1.1 Administration Guide.

Sharing Libraries Across a Cluster

To share libraries across a specific cluster, copy the JAR files to the domain-dir/config/cluster-config-name/lib directory. Then add the path to the JAR files to the System class loader as explained in Using the System Class Loader or to the Shared Chain class loader as explained in Table 2–1.

Some topics in the documentation pertain to features that are available only in domains that are configured to support clusters. Examples of domains that support clusters are domains that are created with the cluster profile or the enterprise profile. For information about profiles, see Usage Profiles in Sun GlassFish Enterprise Server v2.1.1 Administration Guide.

Packaging the Client JAR for One Application in Another Application

By packaging the client JAR for one application in a second application, you allow an EJB or web component in the second application to call an EJB component in the first (dependent) application, without making either of them accessible to any other application or module.

As an alternative for a production environment, you can have the Common class loader load the client JAR of the dependent application as described in Using the Common Class Loader. Restart the server to make the dependent application accessible to all applications or modules deployed on servers that share the same configuration.

To Package the Client JAR for One Application in Another Application

1. Deploy the dependent application.

2. Add the dependent application’s client JAR file to the calling application.

   • For a calling EJB component, add the client JAR file at the same level as the EJB component. Then add a Class-Path entry to the MANIFEST.MF file of the calling EJB component. The Class-Path entry has this syntax:

     Class-Path: filepath1.jar filepath2.jar ...

     Each filepath is relative to the directory or JAR file containing the MANIFEST.MF file. For details, see the Java EE specification.

   • For a calling web component, add the client JAR file under the WEB-INF/lib directory.

3. If you need to package the client JAR with both the EJB and web components, set delegate="true" in the class-loader element of the sun-web.xml file.

   This changes the Web class loader so that it follows the standard class loader delegation model and delegates to its parent before attempting to load a class itself.

   For most applications, packaging the client JAR file with the calling EJB component is sufficient. You do not need to package the client JAR file with both the EJB and web components unless the web component is directly calling the EJB component in the dependent application.

4. Deploy the calling application.

   The calling EJB or web component must specify in its sun-ejb-jar.xml or sun-web.xml file the JNDI name of the EJB component in the dependent application. Using an ejb-link mapping does not work when the EJB component being called resides in another application.

   You do not need to restart the server.