Question

I’m new to EJB, and I’m trying to understand the diference between Stateless and Stateful bean, so I made a simple example to test them.

@Stateless
public class Service {

private int num;

    public Service(){
    }

    public int getNum() {
        return num;
    }

    public void setNum() {
        this.num++;
    }
}

---

@WebServlet("/Controller1")
public class Controller1 extends HttpServlet {
    @EJB
    private Service serv;

    public Controller1() {
        super();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        serv.setNum();
        response.getWriter().println(serv.getNum());
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

}

And the Stateful equivalent:

@Stateful
public class ServiceStateful implements Serializable{
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private int num;

    public ServiceStateful(){
    }

    public int getNum() {
        return num;
    }

    public void setNum() {
        this.num++;
    }
}

---

@WebServlet("/Controller")
public class Controller extends HttpServlet {
    private static final long serialVersionUID = 1L;

    @EJB
    private ServiceStateful serv;

    public Controller() {
        super();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        serv.setNum();
        response.getWriter().println(serv.getNum());
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

}

Both examples act exactly the same, which is surprising for me. Can someone please explain what is the deal here?

Answer 1

You can use instance variables of a stateless session bean, but they’re not guaranteed to be preserved across method calls. If both approaches behave the same, it simply means you’re probably getting the same stateless session bean instance across method calls within the same session.