I have an end point that returns json by its id and if it doesn't find it (id doesn't exist) then it should send a Json object saying not found. Here is my attempt.

PetController.java

@GetMapping("{id}")
    public ResponseEntity<Pet> getPetById(@PathVariable("id") int petId) {
        ResponseEntity<Pet> matchingPet = new ResponseEntity<Pet>(petService.getPetById(petId), HttpStatus.OK);
        if(matchingPet != null) {
            logger.info("pet found");
            return matchingPet;
        }
        else {
            logger.info("pet does not exist");
            return new ResponseEntity<>(HttpStatus.NOT_FOUND);
        }
    }

PetService.java

public interface PetService {
    Pet getPetById(int petId);
}

PetServiceImpl.java

@Service
public class PetServiceImpl implements PetService {

    private PetRepository petrepository;

    public PetServiceImpl(PetRepository petrepository) {
        this.petrepository = petrepository;
    }

    @Override
    public Pet getPetById(int petId) {
            Optional<Pet> pet = petrepository.findById(petId);
            if (pet.isPresent()) {
            return pet.get();
            }
            else {
            return null;
            //return new ResponseEntity<Pet>(HttpStatus.NOT_FOUND); I have tried 
            //this and it doesn't work either and still returns null without the notfound error.

            }
    }

}

It still only returns null. This seems like a logical error because I have a logger in my controller and even when I search a pet with an invalid id that does not exist, it still prints "pet found".

CodePudding user response：

You are creating the instance in your Controller as follows ResponseEntity<Pet> matchingPet = new ResponseEntity<Pet>(petService.getPetById(petId), HttpStatus.OK);. Of course matchingPet will always be not null. Try the following:

@GetMapping("{id}")
public ResponseEntity<Pet> getPetById(@PathVariable("id") int petId) {
    Pet matchingPet = petService.getPetById(petId);
    if(matchingPet != null) {
        logger.info("pet found");
        return new ResponseEntity<Pet>(matchingPet, HttpStatus.OK);
    }
    else {
        logger.info("pet does not exist");
        return new ResponseEntity<>(HttpStatus.NOT_FOUND);
    }
}