You can set values that control the class-loading behavior of an installed Web module. This topic assumes that you installed a Web module on an application server.
An application class loader is the parent of a WAR class loader. The WAR class-loader policy value of an application class loader determines whether the WAR class loader or the application class loader is used to load the contents of the Web module.
The default WAR class loader policy value is Class loader for each WAR file in application. If the policy is set to Class loader for each WAR file in application, then each Web module receives its own class loader whose parent is the application class loader. If the policy is set to Single class loader for application on the settings page of an application class loader, then the application class loader loads the Web module contents as well as the enterprise bean (EJB) modules, shared libraries, resource adapter archives (RAR files), and dependency Java archive (JAR) files associated to an application. Thus, the configuration of the parent application class loader affects the WAR class loader.
Use the administrative console to configure the application and WAR class loaders. Attention: If an application is running, changing an application setting causes the application to restart. On stand-alone servers, the application restarts after you save the change. On multiple-server products, the application restarts after you save the change and files synchronize on the node where the application is installed.
Settings such as Reload classes when application files are updated, Polling interval for updated files and WAR class loader policy can affect Web module class loading.
If WAR class loader policy is set to Class loader for each WAR file in application, then the Web module receives its own class loader and the WAR class-loader policy of the Web module defines the mode for a WAR class loader. If the policy is set to Single class loader for application, then the application class loader loads the Web module contents.
The Web module class-loader mode specifies whether the class loader searches in the parent application class loader or in the WAR class loader first to load a class. The default is to search in the parent application class loader before searching in the WAR class loader to load a class.
Select either of the following values for Class loader order:
| Option | Description |
|---|---|
| Classes loaded with parent class loader first | Causes the class loader to search in the parent application class
loader first to load a class. This is the standard for Development Kit class
loaders and WebSphere Application Server class loaders. If classes and resources needed by the Web module cannot be accessed by the application class loader, but can be accessed by the WAR class loader, specify Classes loaded with application class loader first. If the application class loader cannot find a class, the class loader delegates the request to find the class to its parent, the WebSphere Application Server extensions class loader. If the WebSphere Application Server extensions class loader cannot find the class, the class loader delegates the request to its parent, the bootstrap, extensions, and CLASSPATH class loaders created by the Java virtual machine. Requests can only go to a parent class loader; they cannot go to a child class loader. Thus, if Classes loaded with parent class loader first is specified, the WAR class loader never receives a request to load a class. |
| Classes loaded with application class loader first | Causes the class loader to search in the WAR class loader first to load a class. By specifying Classes loaded with application class loader first, your WAR class loader can override classes contained in the parent application class loader. Attention: Specifying the Classes loaded with application class loader first value might result in LinkageErrors or ClassCastException messages if you have mixed use of overridden classes and non-overridden classes. |