Custom Exception Handling Using ResposneEntityExceptionHandler in Java, Spring:

Sometime Java developers need to create custom exceptions, i.e. Exceptions which are not defined in JDK. Spring provides a exception handler class which help us  to handle custom exceptions gracefully.

Here is  complete code example of creating custom or user defined exception in Java. In this example I created UserNotFoundException  and  RestResponseEntityExceptionHandler class.

Steps for handling Custom Exception:

1. Create Custom Java Class which will inherit Exception Class

public class UserNotFoundException extends Exception {

  private static final String DEFAULT_MESSAGE = "User not found!";

  public UserNotFoundException() {
    super(DEFAULT_MESSAGE);
  }

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

2. Create Exception Handler Java Class

 /**

   * REST  exception handlers defined at a global level for the application

   *

   **/

@ControllerAdvice

public class RestResponseEntityExceptionHandler extends ResponseEntityExceptionHandler {

  @ExceptionHandler(value = {UserNotFoundException.class})

  protected ResponseEntity<RestResponse> handleUserNotFound(UserNotFoundException ex, WebRequest request) {

    return handleException(ex.getMessage(), HttpStatus.FORBIDDEN);

  }

  private ResponseEntity<RestResponse> handleException(String message, HttpStatus status) {

    LOGGER.error(message);

    return new ResponseEntity<RestResponse>(new RestResponse(Boolean.FALSE, ImmutableList.of(message), null), status);

  }

}

ResponseEntityExceptionHandler: A class that wish to provide centralized exception handling across all @RequestMapping methods through @ExceptionHandler methods.

This  class provides an @ExceptionHandler for handling standard Spring MVC exceptions that returns a ResponseEntity.

 @ControllerAdvice: A class annotated with it will act as global handler class for all controllers. It is used to define @ExceptionHandler methods that apply to all @RequestMapping methods.

3. Create service which will throw UserNotFoundException.class if user doesn't found in the DB.

public interface UserService {

  User findByEmailId(String emailId) throws UserNotFoundException;

}


@Service
public class UserServiceImpl implements UserService {

    @Autowired
    private UserRepository userRepository;


    @Override
    public User findByEmailId(String emailId) throws UserNotFoundException {

        if ((emailId == null) || (emailId == "")) {
            throw new IllegalArgumentException("userId not found ");
        }
        User user = userRepository.findByEmail(emailId);
        if (user == null) {

            throw new UserNotFoundException();
        }

        return user;
    }
}

4. Create Controller which will call service method

@Controller

@RequestMapping(value = "/user")

public class UserController {

  @Autowired

  private UserService userService;

 @RequestMapping(value = "/findby-email", method = RequestMethod.POST)
 @ResponseBody

    public ResponseEntity<RestResponse> findByEMail(@RequestParam String email) throws       UserNotFoundException {

        return new ResponseEntity<RestResponse>(new RestResponse(Boolean.TRUE, "Succesfully Logged In!", userService.findByEmailId(email)), HttpStatus.OK);
    }

}

For complete running application refer Github Repository

Keywords: GloabalExcetionHandling, SpringMVC, ResponseEntityExceptionHandler, @ControllerAdvice, REST