Usage

To signal a problem from a controller, build a Problem, attach any contextual info, and throw it:

@Controller("/pets")
public class PetController {

    Map<String, Pet> petRepository = new ConcurrentHashMap<>();

    @Get("/{name}")
    public Pet findPetByName(@PathVariable String name) {
        return petRepository.computeIfAbsent(
            name,
            (missing) -> {
                throw Problem.of(HttpStatus.NOT_FOUND.getCode(), PetProblemCode.PetNotFound)
                    .withInfo("name", missing)
                    .toThrowable();
            }
        );
    }

}

With the Micronaut integration in place, the thrown ThrowableProblem is translated into an application/problem+json HTTP response automatically — there’s no extra controller-level error handling to write.

The code and detail come from the ProblemCode enum referenced above. See Defining Problem Codes for how to define one.

Adding context

Use withInfo(…) to attach the data that explains this specific occurrence of the problem:

throw Problem.of(HttpStatus.BAD_REQUEST.getCode(), PetProblemCode.InvalidName)
    .withInfo("name", suppliedName)
    .withInfo("reason", "must be lowercase")
    .toThrowable();

The info map is serialized as part of the response body, so callers can act on it programmatically.