Configuring class loaders of a WebSphere server

You can configure the application class loaders for an application server and for a Java™ virtual machine (JVM). Class loaders enable applications that are deployed on the application server to access repositories of available classes and resources.

1. Configure the class loaders for the application server.
   1. Click Servers > Server Types > WebSphere application servers > server_name to access an application server settings page.
   2. Specify the application class-loader policy for the application server.

      The application class-loader policy controls the isolation of applications that run in the system (on the server). An application class loader groups enterprise bean (EJB) modules, shared libraries, resource adapter archives (RAR files), and dependency Java archive (JAR) files associated to an application. Dependency JAR files are JAR files that contain code which can be used by both enterprise beans and servlets. The application class-loader policy controls whether an application class loader can be shared by multiple applications or is unique for each application.

      Use the application server settings page to specify the application class-loader policy for the server:

      Single

      Applications are not isolated from each other. Uses a single application class loader to load all of the EJB modules, shared libraries, and dependency JAR files in the system.

      Multiple

      Applications are isolated from each other. Gives each application its own class loader to load the EJB modules, shared libraries, and dependency JAR files of that application.

   3. Specify the application class-loader mode for the application server.

      The application class loading mode specifies the class-loader mode when the application class-loader policy is Single.

      On the application server settings page, select either of the following values:

      Classes loaded with parent class loader first

      Causes the class loader to delegate the loading of classes to its parent class loader before attempting to load the class from its local class path. Classes loaded with parent class loader first is the default value for class loading mode.

      This value is also known as parent first.

      Classes loaded with local class loader first (parent last)

      Causes the class loader to attempt to load classes from its local class path before delegating the class loading to its parent. Using this policy, an application class loader can override and provide its own version of a class that exists in the parent class loader.

2. Specify the class-loader mode for the class loader in the JVM configuration.
   1. On the application server settings page, click Java and Process Management > Class loader to access the Class loader page.
   2. On the Class loader page, click New to access the settings page for a class loader.
   3. On the class loader settings page, specify the class loader order.

      The Classes loaded with parent class loader first value causes the class loader to delegate the loading of classes to its parent class loader before attempting to load the class from its local class path.

      The Classes loaded with local class loader first (parent last) value causes the class loader to attempt to load classes from its local class path before delegating the class loading to its parent.

   4. Click OK.
   An identifier is assigned to a class-loader instance. The instance is added to the collection of class loaders shown on the Class loader page.