[FIXED] Spring: Inconsistent precedence of exception handling vs try catch block

Issue

have a spring boot/jpa application. In the code below - if the save call in createEntity() method raises a DataIntegrityViolationException, the exception is caught in the EntityExceptionHandler - not in the catch (of the try-catch) block. If the @Transactional annotation is removed from the createEntity method (service class), the DataIntegrityViolationException is caught in the catch block not in the exception handler.

Could this be explained? I don't understand the inconsistency.

Also if a try-catch block is placed around the createEntity call in EntityController, the exception is caught in the catch block - not in the exception handler - irrespective of whether the @Transactional annotation is set. Could this be explained also?

Thank you.

public class EntityController {
    @PostMapping(value = "/entities")
    @ResponseBody
    public ResponseEntity postEntity(@RequestBody entity) {
        entityService.createEntity(entity);
        return ResponseEntity.status(HttpStatus.CREATED)...;
    }
}

@Repository("EntityRepository")
public interface EntityRepository extends JpaRepository<Entity, UUID> {}

@Service
public class EntityServiceImpl implements EntityService {
    @Autowired
    private EntityRepository entityRepository;

    @Override
    @Transactional
    public void createEntity() {
        Entity entity = new Entity(...);
        try {
            entityRepository.save(entity);
        } catch (DataIntegrityViolationException ex) {...}
    }
}

@ControllerAdvice
public class EntityExceptionHandler extends ResponseEntityExceptionHandler {
    @ExceptionHandler(DataIntegrityViolationException.class)
    @ResponseBody
    public ResponseEntity<Object> handleDataIntegrityViolationException(DataIntegrityViolationException ex, WebRequest request) {
        return ResponseEntity.status(HttpStatus.CONFLICT).headers(new HttpHeaders()).body("");
    }
}

Solution

The exception happens as soon as the transaction is submitted to the database. If the method is annotated with @Transactional, the submit happens in the "wrapper" and not within the createEntity method itself. Therefore the try-catch block has no effect.

Pseudocode with @Transactional:

beginTransaction()
try {
  entityRepository.save(...)
} catch (....) {}
endTransaction() <- here the exception is thrown

Answered By - Martin Theiss
Answer Checked By - Timothy Miller (JavaFixing Admin)