h1.  Via annotation

{code:title=Usable by EJB, Interceptor, Servlet, Filter, or Listener}
package org.superbiz.refs;

import javax.annotation.Resource;
import javax.ejb.Stateless;
import javax.naming.InitialContext;
import javax.sql.DataSource;

@Stateless
@Resource(name = "myFooDataSource", type = DataSource.class)
public class MyDataSourceRefBean implements MyBeanInterface {

    @Resource
    private DataSource myBarDataSource;

    public void someBusinessMethod() throws Exception {
        if (myBarDataSource == null) throw new NullPointerException("myBarDataSource not injected");

        // Both can be looked up from JNDI as well
        InitialContext context = new InitialContext();
        DataSource fooDataSource = (DataSource) context.lookup("java:comp/env/myFooDataSource");
        DataSource barDataSource = (DataSource) context.lookup("java:comp/env/org.superbiz.refs.MyDataSourceRefBean/myBarDataSource");
    }
}
{code}

h1. Via xml

The above @Resource annotation usage is 100% equivalent to the following xml.

{code:xml|title=ejb-jar.xml or web.xml}
<resource-ref>
    <res-ref-name>myFooDataSource</res-ref-name>
    <res-type>javax.sql.DataSource</res-type>
</resource-ref>
<resource-ref>
    <res-ref-name>org.superbiz.refs.MyDataSourceRefBean/myBarDataSource</res-ref-name>
    <res-type>javax.sql.DataSource</res-type>
    <injection-target>
        <injection-target-class>org.superbiz.refs.MyDataSourceRefBean</injection-target-class>
        <injection-target-name>myBarDataSource</injection-target-name>
    </injection-target>
</resource-ref>
{code}