Singleton EJB在外部EJB容器中的行为应相同，但不应

Question

I have implemented a dummy data repository in a singleton bean for development purposes. The singleton bean's constructor creates dummy data and there are methods to retrieve, insert, update and delete dummy data.

When I unit test it, checking that objects being inserted and updated can be retrieved in the same state they were inserted and updated (ie property-by-property equality), the unit test passes. In this test, I just instantiate the singleton bean as a regular object, ie via its constructor. When I actually use the singleton bean by injecting it into a @RequestScoped JSF backing bean (which leaves bean creation to the EJB container), after updating a data item and subsequently retrieving it by its ID, the update seems to be lost and the old field values are used. So the bean doesn't behave the same in and out of the container. And yet, there is a System.out.println in the constructor that is only executed once, so in that sense it appears to instantiate only once.

The singleton bean is structured like this:

@ConcurrencyManagement(ConcurrencyManagementType.BEAN)
@Singleton
@LocalBean
public class DummyDataRepository {
    public DummyDataRepository() {
        // Initial dummy data created here.
    }

    public final synchronized Foo findFooById(int id) {
        // Retreive a Foo by ID.
        // ...
    }

    public final synchronized void addFoo(Foo foo) {
        // Add the Foo.
        // ...
    }

    public final synchronized void updateFoo(Foo foo) {
        // Find the existing Foo by foo.id and replace it with foo.
        // ...
    }

    public final synchronized void deleteFoo(int id) {
        // Find the existing Foo by id and delete it.
        // ...
    }
}

There doesn't appear to be any reason that the bean should produce different results in and out of the EJB container. It doesn't use any external resources. Synchronization is bean managed (so should be the same in that regard). The bean is declared as singleton. But in the container it appears to be acting as a stateless session bean.

I'm using GlassFish 3.1.2.2.

Update: I changed the bean from @javax.ejb.Singleton to @javax.enterprise.context.ApplicationScoped (and inject it where required via @javax.inject.Inject instead of @javax.ejb.EJB ) and it now works as expected. Yet there should be no difference between the two. It seams that, although the singleton EJB is being instantiated only once, it somehow reverts its state between method invocations.

Answer 1

Public methods in a singleton bean should not be declared as final . I had declared them as final because I was calling them from the constructor to populate collections with the initial dummy dataset. When not declared as final, NetBeans correctly warned about calling methods from a base class constructor that could be overridden in a subclass. When not declared as final, I was getting a NullPointerException simply by calling the singleton bean's own public method from the constructor. So there must be some kind of proxying that occurs for non-final methods.

I'm still not sure why it appears as though results of final methods are cached (ie getting stale results). But I have my answer, so I'm happy enough with that.