<Context ...>
  ...
  <Resource name="jdbc/EmployeeDB"
            auth="Container"
            type="javax.sql.DataSource"
            username="dbusername"
            password="dbpassword"
            driverClassName="org.hsql.jdbcDriver"
            url="jdbc:HypersonicSQL:database"
            maxTotal="8"
            maxIdle="4"/>
  ...
</Context>

Context initCtx = new InitialContext();
Context envCtx = (Context) initCtx.lookup("java:comp/env");
DataSource ds = (DataSource)
  envCtx.lookup("jdbc/EmployeeDB");

Connection conn = ds.getConnection();
... use this connection to access the database ...
conn.close();