Application client is another type of Java EE module, the least utilized one. It attempts to wrap up Java SE application, deploy it to application server, and make use of deployed EJB, platform services and resources.

The following application-client.xml declares an env-entry, ejb-ref and resource-ref.

<?xml version="1.0" encoding="UTF-8"?>
<application-client xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="5"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/application-client_5.xsd">

 <display-name>A sample application client</display-name>

 <env-entry>
   <description>admin email</description>
   <env-entry-name>adminEmail</env-entry-name>
   <env-entry-value>admin@example.x</env-entry-value>
 </env-entry>

 <ejb-ref>
   <ejb-ref-name>ejb/testBean</ejb-ref-name>
   <remote>test.TestRemoteInterface</remote>
   <ejb-link>TestBean</ejb-link>
 </ejb-ref>

 <resource-ref>
   <res-ref-name>HRDS</res-ref-name>
   <res-type>javax.sql.DataSource</res-type>
   <mapped-name>jdbc/__default</mapped-name>
 </resource-ref>

</application-client>

The env-entry can be looked up with name "java:comp/env/adminEmail", or injected into the application client main class or its superclasses. For example:

@Resource(name="adminEmail")
//use static modifier in application client main class only
private static String adminEmail;

The ejb-ref and resource-ref can be looked up with names "java:comp/ejb/testBean" and "java:comp/env/HRDS", respectively.

The reason I include ejb-ref and resource-ref is to show how they fit in descriptors. In Java EE 5 and later, it is easier to use @EJB and @Resource to declare and inject them into component classes.