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One popular question in JBoss forums is the correct placement of shared libraries with Enterprise Application deployed on JBoss. In this short tutorial we will show the available options.

A typical Enterprise application is made up of a Front-end Layer, a Persistence Layer and some common Classes referenced by both layers.

Placing the common Classes in an EAR archive allows the EJB and Web Classloader to resolve correctly the utility Classes referenced, however you have to instruct JBoss about these Classes. You have basically three options for referencing utility Classes:

Option 1: Declare the shared libs in application.xml

This is the most portable solution, since the application.xml descriptor allows your application to declare external Java modules by adding the <Java> module.

Here's an example:  

<application>
 
  <module>
    <web>
      <web-uri>TestWeb.war</web-uri>
      <context-root>testWeb</context-root>
    </web>
  </module>
  
  <module>
    <ejb>TestEJB.jar</ejb>
  </module>
   
  <module>
    <java>Utility.jar</java>
  </module>
    
</application>

By placing libraries or configuration files in the "lib" folder (at the root of your EAR), you will be able to resolve your class/files without the need to add any configuration.
Though this is the fastest solution, it might not be supported in all application servers. For example Bea Weblogic uses the APP-INF/lib to load common libraries

Option 3: Add a jboss-app.xml configuration file

If you want even more customization for your application, you can use a JBoss specific deployment descriptor, named jboss-app.xml which is to be placed in the META-INF folder of your EAR.
Here's a sample of it:  

<!DOCTYPE jboss-app PUBLIC "-//JBoss//DTD J2EE Application 5.0//EN"
"http://www.jboss.org/j2ee/dtd/jboss-app_5_0.dtd" >
<jboss-app> 
   <library-directory>APP-INF/lib</library-directory>
</jboss-app>