Lookup API NetBeans Platform + Maven: loosely coupled modules

Question

I'm developing a NetBeans platform application and want to use lookup api to get implementations for specific interfaces, still keeping everything loosely coupled. But the lookup can't find any service provider.

Well, I created:

• a Module (A) that contains two Interfaces (Prot,Com) and a class to show some GUI.
• a Module (B) that contains an implementation of interface Prot
• a Module (C) that contains an implementation of interface COM.

To register an implementation i used @ServiceProvider annotation. For Examble in Module B:

@ServiceProvider(service = Prot.class)
class ProtImpl implements Prot
{
   @Override
   ...
}

I defined the default-constructor, that is needed, if you use @ServiceProvider annotation. I defined a dependency on Module A because B need to know something about the interface.

Lookup Examble in Module A:

private void printImplNames()
{
   Prot prot = Lookup.getDefault().lookup(Prot.class);
   prot.getName(); // <--- Null-Pointer
}

Now if I look up the implementation of interface Prot, I get a null pointer exception. With other words, there is no implementation registered. The lookup cant find any service provider. Annotation processcor works fine, because files in META-INF/.../ directory were created.

The only thing that seems to work is to define a dependency on Module B in Module A BUT in this way the aspect of loosley coupled modules is lost.

I followed intructions on NetBeans Platform Website and NetBeans Platform 7 Book but nothing seems to work. Hope somebody can help me to solve that problem.

Thanks ;)

Answer 1

I've created a working example for this situation located at GitHub.

https://github.com/flinkgutt/stackoverflow/tree/master/LooseCoupling