CDI-JSF: Using CDI alternatives priority (@Priority)

Before you read this post please read: Use a CDI alternative as a mock implementation for a stateless session bean

So, since you are familiar with the above post, now let's suppose that we have multiple mock implementations. In such cases, the problem is how to instruct the container to choose between the implementations? The answer relies on alternatives priority!

Basically, we annotate each mock implementation with @Priority and provide a number as the level of priority. The higher number has the higher priority. Here it is three mock implementations with priorities 1,2 and 3:

@Priority(1)

@Alternative

@Stateless

public class FooServiceMock implements IFooService {

 @Override

 public List getAllFoo() {

  return Arrays.asList("foo 1", "foo 2", "foo 3");

 }

}

@Priority(2)

@Alternative

@Stateless

public class BestFooServiceMock implements IFooService {

 @Override

 public List getAllFoo() {

  return Arrays.asList("best foo 1", "best foo 2", "best foo 3");

 }

}

@Priority(3)

@Alternative

@Stateless

public class GreatFooServiceMock implements IFooService {

 @Override

 public List getAllFoo() {

  return Arrays.asList("great foo 1", "great foo 2", "great foo 3");

 }

}

The mock implementation annotated with @Priority(3) has the higher priority. When we run the below code CDI will automatically choose the GreatFooServiceMock:

@Named

@RequestScoped

public class FooBean {

 private static final Logger LOG = Logger.getLogger(FooBean.class.getName());

 @Inject

 private IFooService fooService; // choose GreatFooServiceMock

 public void loadAllFoo() {

  List allfoo = fooService.getAllFoo();

  LOG.log(Level.INFO, "allfoo:{0}", allfoo);

 }

}

Now, we can also write a test using CDI-Unit as below (this will also choose the GreatFooServiceMock):

@RunWith(CdiRunner.class)

@ActivatedAlternatives({FooServiceMock.class, BestFooServiceMock.class, GreatFooServiceMock.class})

public class FooBeanTest {

   

 @Inject

 FooBean fooBean;

 @Test

 @InRequestScope

 public void testStart() {

  fooBean.loadAllFoo();

 }   

}

We can use the @Priority annotation to specify alternatives globally for an application that consists of multiple modules like this:

@Alternative
@Priority(Interceptor.Priority.APPLICATION+10)
public class ...

The complete example is available here.