JAX-RS supports handling custom exceptions — thrown in either EJBs or CID beans — to custom HTTP responses.

Assuming we have an “exceptional” EJB:

@Stateless
public class Hello {

 public String greeting() {
 if (new Random().nextBoolean())
 throw new GreetingException("Could not greet");

 return "hello";
 }

}

@ApplicationException
public class GreetingException extends RuntimeException {

 public GreetingException(String message) {
 super(message);
 }

}

The EJB is used in our JAX-RS resource:

@Path("hello")
public class HelloResource {

 @Inject
 Hello hello;

 @GET
 public String hello() {
 return hello.greeting();
 }

}

Now to map the occurring exception to a custom HTTP response we can define a JAX-RS ExceptionMapper.

@Provider
public class GreetingExceptionMapper implements ExceptionMapper<GreetingException> {

 @Override
 public Response toResponse(GreetingException exception) {
 return Response.status(Response.Status.CONFLICT)
 .header("Conflict-Reason", exception.getMessage())
 .build();
 }

}

The exception mapper is registered as a JAX-RS extension (by @Provider) and will handle any GreetingException thrown by a resource method.

The example will occasionally output HTTP 409 Conflict with header Conflict-Reason: Could not greet.

If a CDI managed bean is used instead of an EJB, the @ApplicationException annotation is not required.