Basic Extensions using Liberty Libraries

This feature enables the configuration of Basic Extensions using Liberty Libraries (BELL).

The BELL feature enables libraries to define the implementation of an Open Liberty SPI or API with Java ServiceLoader configuration files. These files are included in the /META-INF/services/ directory of the library JAR file.

With the BELL feature, a library declares a /META-INF/services/ resource with the name of the fully qualified API or SPI interface, and provides a class that implements the interface. The feature processes the /META-INF/services/ resources and provides the library interface implementation to the Open Liberty runtime.

Enabling this feature

To enable the Basic Extensions using Liberty Libraries 1.0 feature, add the following element declaration into your server.xml file, inside the featureManager element:



Configure a servlet filter for applications

In certain scenarios, a servlet filter implementation must be applied to all applications that are deployed to Open Liberty. For example, a servlet filter might be used to add new headers to each request. The ServletContainerInitializer interface provides an onStartup method that can be used to add a servlet filter implementation class to all applications.

The BELL feature can be used to configure a library that provides a ServletContainerInitializer implementation as a service. The ServletContainerInitializer service onStartup method is called by Open Liberty for each application that starts. In the following example, a ServletContainerInitializer implementation is configured to add a servlet filter implementation with each ServletContext object that is in a Java file. The ServletContext.addFilter(String, Filter) method is used by the onStartup method to add the servlet filter implementation:

public class SCI implements ServletContainerInitializer {
  public void onStartup(Set<Class<?>> arg0, ServletContext arg1)
    throws ServletException {
    arg1.addFilter("myFilter", MyFilter.class).addMappingForUrlPatterns(null, false, "/*");

To register the ServletContainerInitializer interface that adds the servlet filter for an application, a class name is specified in the library JAR file. The library JAR file contains a META-INF/services/javax.servlet.ServletContainerInitializer file that specifies the fully qualified ServletContainerInitializer implementation class name that is contained in the library. The following example uses the file element to add the path to jar JAR file to the library:

<library id="init">
  <file name="path to jar"/>

<bell libraryRef="init"/>

Add a custom user registry from a shared library

The BELL feature can load a custom user registry with a custom user registry JAR file that is stored in a shared library on the server. The following example adds the resources/sharedLib shared library that contains the bellsCur.jar JAR file. The bell element references this library to load the custom user registry:

<library id="bellsCurLib" name="bellsCurLib">
         <file name="${server.config.dir}/resources/sharedLib/bellsCur.jar"></file>
 <bell libraryRef="bellsCurLib"></bell>

Feature configuration elements

Supported Java versions

  • JavaSE-1.8

  • JavaSE-11.0

  • JavaSE-15.0

Features that enable this feature

Developing a feature that depends on this feature

If you are developing a feature that depends on this feature, include the following item in the Subsystem-Content header in your feature manifest file.; type="osgi.subsystem.feature"