3 Replies Latest reply on Sep 6, 2010 9:44 AM by nimo22

    constructor not called of embeeded objects

    nimo22
    nimo22 Sep 3, 2010 5:44 AM

      I have a no-scoped (entity) bean:


      public class User implements Serializable{ 
...

private Role role;
// getter/setter

}



      I inject a new instance of User into my bean:


      @SessionScoped @Named("bean")
public class MyBean implements Serializable{ 

@Inject Users findUser;

}




      when referring in jsf,
      then it throws a java.lang.NullPointerException,
      because the property role of instance user is null.



      <h:panelGrid columns="2">
<h:outputText value="ID-User" />
<h:inputText value="#{bean.findUser.id}" converter="javax.faces.Integer" />

<h:outputText value="ID-Role" />
<h:inputText value="#{bean.findUser.role.id}" converter="javax.faces.Integer"/>
</h:panelGrid>




      So I have to use something like this in my code:


      @SessionScoped @Named("bean")
public class MyBean implements Serializable{ 

@Inject Users findUser;

@PostConstruct
public void initialize()
{
// instantiate a new instance of role to avoid the NPE
findUsers.setRole(new Role());
}

}



      Why does CDI not instantiate a new instance automatically?
      Of course, a new instance of Users is injected,
      but Users has objects within, which should also get a new instance (when needed).


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        • 1. Re: constructor not called of embeeded objects
          pmuir
          pmuir Sep 6, 2010 6:06 AM (in response to nimo22)

          Do you @Inject Role into Users?

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          • 2. Re: constructor not called of embeeded objects
            nimo22
            nimo22 Sep 6, 2010 6:43 AM (in response to nimo22)

            No, I did not @Inject Role into Users.


            That was my fault.
            I have thought, weld creates (inject) new instances of objects automatically.



            So I have to use this code (both versions work):



            version 1:


            public class User implements Serializable{ 
...

private @Inject Role role;
// getter/setter

}




            version 2:



            public class User implements Serializable{ 
...

private Role role = new Role();
// getter/setter

}




            I guess, I will use version 2 as these objects are pojos (entitybeans).

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            • 3. Re: constructor not called of embeeded objects
              nimo22
              nimo22 Sep 6, 2010 9:44 AM (in response to nimo22)

              Another thing is:



              There are cases, I do need a new Role-Object when instantiating a new User-Object.
              But there are also cases, I do not need a new Role-Object  - so (for a big project), it is a waste to create a new Instance without needing it. I can use a NullObjectPattern, but this is annoying.


              Should I do it that way:




              public class User implements Serializable{ 
...

// this is actually null,
// I should avoid using Role role = new Role() or @Inject Role role
// because it will be a waste, if I do not need it.
private Role role;
// getter/setter

}

public class MyBean implements Serializable{ 
...

@Inject User u;

@PostConstruct
public void init()
{

// this is a little annoying:
// I can eliminate that boilerplate-code by creating a new instance of role 
// within a user-class, but this would be a waste if I do not need a role-instance
u.setRole(new Role());
}

}





              So, how can I solve that in a pretty way?
              When using @Inject role, than weld does also create a new Instance within the class User even I do not need it.


              Does Weld @Inject handles the NullObjectPattern internally?


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