Via annotation

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");
    }
}