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synchronizationseam

Singleton with JBoss SEAM

I have the following code:

@Name("myService")
@Scope(ScopeType.APPLICATION)
@Stateless
public class MyService {
  private Service service;

  private Service getService() {
    if (service == null) {
      service = Service.create(url, new QName("URL",
        "Envelope"));
    }

    return service;
  }    

  public synchronized Port getPort() {
    return getService().getPort();
  }
}

And getPort method is invoked from different threads. "Service.create" takes a lot of time and I've found that actually it is invoked more than once. So it looks like more than one instance of MyService class is created and that's why synchronized doesn't help.

I've changed annotations to:

@AutoCreate
@Startup
@Name("myService")
@Scope(ScopeType.APPLICATION)

And now it seems to work fine: only one instance is created and access to the getPort() method is synchronized.

Could anyone explain why the first case doesn't wok as expected?

Solution

  • A @Stateless bound to an Application scope is an oxymoron

    you are asking Java EE to provide a component that has no state, to live in the Application Scope, shared by all users

    When you removed the @Stateless annotation, seam handled the instance of the component and placed it in the Application Scope, it also created it at startup, hence having a singleton