Providing global libraries for all Java EE applications

You can provide global libraries that can be used by any Java™ EE application. You do this by putting the JAR files for those libraries in a global library directory, then specifying use of global libraries in the class loader configuration for each application. However, the global libraries cannot be used by other applications, for example, by OSGi applications.

Open Liberty The latest documentation about class loader configuration for Liberty is available on the Open Liberty website.

About this task

Under the user directory specified by using the environment variable WLP_USER_DIR, there are the following locations in which you can place global libraries:
  • ${shared.config.dir}/lib/global
  • ${server.config.dir}/lib/global
If there are files present in these locations at the time an application is started, and that application does not have a <classloader> element configured, the application uses these libraries. If a class loader configuration is present, these libraries are not used unless the global library is explicitly referenced.
Attention: If you use global libraries, you are advised also to configure a <classloader> element for every application. The servlet specification requires applications to share the global library class loader in their class loader parent chain. This breaks the separation of class loaders for each application that is otherwise possible. So, applications are more likely to have long-lasting effects on classes loaded in Liberty and on each other, and class space consistency issues are more likely to arise between applications, especially as features are added and removed from a running server. None of these considerations apply for applications that specify a <classloader> element in their configuration, because they maintain this separation.

Example

In the following example, an application called Scholar is configured to use a common library called Alexandria, and also to use the global library.

In the server.xml file, or an included file, enable the global library for an application by adding the following code:
<application id="" name="Scholar" type="ear" location="scholar.ear">
  <classloader commonLibraryRef="Alexandria, global" />
</application>
The settings for the global library can also be configured explicitly, as a library element with the special ID global. For example:
<library id="global">
  <fileset dir="/path/to/folder" includes="*.jar" />
</library>