How To Expose And Inject A POJO ...Into An EJB 3

A POJO:

public class CustomResource{

    public final static String JNDI_NAME = "theName";

    public void doSomething(){

        System.out.println("#Done !");

    }

}

can be easily exposed (=bound to JNDI) with a singleton bean:

@Startup

@Singleton

public class ResourceBinder {

    @PostConstruct

    public void bindResources(){

        try {

            Context context = new InitialContext();

            context.rebind(CustomResource.JNDI_NAME, new CustomResource());

            System.out.println("Resource bound...");

            System.out.println(" " + context.lookup(CustomResource.JNDI_NAME));

        } catch (NamingException ex) {

            throw new IllegalStateException("Cannot bind resource " +ex,ex);

        }

    }

 

...and injected into a Stateless, Stateful, Singleton Bean or other resources like e.g. Servlets, Backing Beans etc:

@Singleton

@Startup

@DependsOn("ResourceBinder")

public class CustomResourceClient {

    @Resource(mappedName=CustomResource.JNDI_NAME)

    private CustomResource resource;

    @PostConstruct

    public void invokeResource(){

        this.resource.doSomething();

        System.out.println("----Resource invoked");

    }

}

 You should see the following output in the log files (tested with Glassfish v3b70):

INFO: Portable JNDI names for EJB CustomResourceClient : [java:global/ResourceBinder/CustomResourceClient!com.abien.patterns.kitchensink.resourcebinder.CustomResourceClient, java:global/ResourceBinder/CustomResourceClient]

INFO: Portable JNDI names for EJB ResourceBinder : [java:global/ResourceBinder/ResourceBinder, java:global/ResourceBinder/ResourceBinder!com.abien.patterns.kitchensink.resourcebinder.ResourceBinder]

INFO: Resource bound...

INFO:  com.abien.patterns.kitchensink.resourcebinder.CustomResource@50058560

INFO: #Done !

INFO: ----Resource invoked 

The ResourceBinder project was tested with NetBeans 6.8beta and Glassfish v3b70. It was pushed into: http://kenai.com/projects/javaee-patterns/.  Closing remarks:

  1. It is easier and better to declare a POJO as a Session Bean. You gain a lot with almost no trade-offs.
  2. You should be careful with the concurrency. Such an exposed POJO will be accessed by several threads / transactions concurrently.
  3. You easily inject POJOs with interceptors as well.
  4. You should never use System.out.println on the server in production, because of:
     public void println(String x) {
    synchronized (this) {
       print(x);
       newLine();
    }
        }

 [See "Resource Binder" pattern, page 243,  in "Real World Java EE Patterns Rethinking Best Practices" book for more in-depth discussion] 


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Comments:

Adam, have you seen what JSR-299 can do in EE6?

Posted by Gavin on November 02, 2009 at 06:43 PM CET #

Hi Gavin,

sure. Even presented JSR-299 last week during a Java EE 6 workshop. Weld is great :-). However, you can implement 80 % of all use cases efficiently with vanilla EJBs.
Btw. JSR-330 is also interesting :-),

thanks for your comment!,

adam

Posted by Adam Bien on November 02, 2009 at 06:52 PM CET #

Adam, is it advisable to use this approach to pass technical user/context data from say a Servlet to an EJB (instead of ThreadLocal, you know what I mean ;-) )?
Is context.rebind an expensive operation since in my case I would do a lot of rebinds?

Posted by Detlef on November 02, 2009 at 11:31 PM CET #

Detlef,

it is absolutely not advisable. I forgot your email - sorry.

Gruss :-),

adam

Posted by Adam Bien on November 03, 2009 at 09:53 AM CET #

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