Question

I’m sure this is a beginner error…

So I have a Java EE 6 application with entities, facades (implementing the persistence layer) and Stateless Session Beans (EJB3) with Remote interfaces (providing access to the entities via facades).

This is working fine. Via the SLSB I can retrieve and manipulate entities.

Now, I’m trying to do this from a Web Application (deployed on the same Glassfish, entity+interface definitions from Java EE app imported as separate jar). I have a Servlet, that receives an instance of the SLSB injected. I get it to retrieve an entity, and the following happens (I can see it in the logs):

• the remote SLSB gets instantiated, its method called
• SLSB instantiates the facade, calls the ‘get’ method
• facade retrieves instance of entity from DB, returns it
• SLSB returns the instance of the entity to the caller
  • (all is good until here)
• calling servlet receives .. an empty instance of the entity !!

What is going wrong? This should work, right?

MyServlet:

public class MyServlet extends HttpServlet {

  @EJB
  private CampaignControllerRemote campaignController; // remote SLSB

  protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/plain");
    PrintWriter out = response.getWriter();
    try {
      Campaign c = campaignController.getCampaign(5L); // id of an existing campaign
      out.println("Got "+ c.getSomeString()); // is null !!
    } finally { 
        out.close();
    }
  }
  ...
}

Pls let me know if you want to see other code, and I’ll update the post.

Answer 1

… oh boy, this is sort of embarrassing …

It turns out, I have been ignoring a nice little warning regarding the use of Vector as type of a field that holds a @xxToMany relationship with FetchType.LAZY:

Element [field someField] within
entity class [class Campaign] uses a
collection type [class
java.util.Vector] when the JPA
specification only supports
java.util.Collection, java.util.Set,
java.util.List, or java.util.Map.
This type is supported with eager
loading; using lazy loading with this
collection type requires additional
configuration and an IndirectContainer
implementation that extends [class
java.util.Vector] or setting the
mapping to use basic indirection and
the type to be ValueholderInterface.

Two possible solutions can fix my behaviour:

• use FetchType.EAGER (then I could stay with Vector)
• use List (as the spec says…)