Exception handling using handlers spring boot

Question

I am a newbie with spring and spring boot. After creating a simple REST API to perform CRUD operations on Users i have also created custom exception handlers to catch any exceptions occurred in the application. Here is the code which i have written

The controller class

public class UserController {

    @Autowired
    private IUserService userService;

    @ApiOperation(value = "View list of all users", response = Iterable.class)
    @RequestMapping(value = "/users", method = RequestMethod.GET)
    public @ResponseBody List<User> getAll() throws EntityNotFoundException {
        return userService.query();
    }

    @ApiOperation(value = "View a specific user", response = User.class)
    @RequestMapping(value = "/users/{id}", method = RequestMethod.GET, produces = { MediaType.APPLICATION_JSON_VALUE })
    public @ResponseBody List<User> getUser(@PathVariable(value = "id") String userid) throws EntityNotFoundException {
        return userService.query(userid);
    }

    @ApiOperation(value = "create a user")
    @RequestMapping(value = "/users", method = RequestMethod.POST, produces = { MediaType.APPLICATION_JSON_VALUE })
    public ResponseEntity<HttpStatus> createUser(@Valid @RequestBody User user) throws Exception {
        userService.add(user);
        return ResponseEntity.ok(HttpStatus.OK);
    }

    @ApiOperation(value = "update a user")
    @RequestMapping(value = "/users", method = RequestMethod.PUT, produces = { MediaType.APPLICATION_JSON_VALUE })
    public ResponseEntity<User> updateUser(@Valid @RequestBody User entity) throws Exception {
        User user = userService.update(entity);
        if (user == null) {
            return ResponseEntity.notFound().build();
        }
        return ResponseEntity.ok(user);
    }

    @ApiOperation(value = "delete a user")
    @RequestMapping(value = "/userid/{id}", method = RequestMethod.DELETE, produces = {
            MediaType.APPLICATION_JSON_VALUE })
    public ResponseEntity<HttpStatus> deleteUser(@PathVariable(value = "id") String userid) throws Exception {
        String result = userService.remove(userid);
        if (result.equals(null)) {
            return ResponseEntity.notFound().build();
        }
        return ResponseEntity.ok(HttpStatus.OK);
    }

}

Exceptions handlers annotated class with @Controlleradvice

@Order(Ordered.HIGHEST_PRECEDENCE)
@ControllerAdvice
public class RestExceptionHandler extends ResponseEntityExceptionHandler {

    /**
     * Handles javax.validation.ConstraintViolationException. Thrown
     * when @Validated fails.
     *
     * @param ex
     *            the ConstraintViolationException
     * @return the ApiError object
     */
    @ExceptionHandler(javax.validation.ConstraintViolationException.class)
    protected ResponseEntity<Object> handleConstraintViolation(javax.validation.ConstraintViolationException ex) {
        ApiError apiError = new ApiError(BAD_REQUEST);
        apiError.setMessage("Validation error");
        return buildResponseEntity(apiError);
    }

    /**
     * Handles EntityNotFoundException. Created to encapsulate errors with more
     * detail than javax.persistence.EntityNotFoundException.
     *
     * @param ex
     *            the EntityNotFoundException
     * @return the ApiError object
     */
    @ExceptionHandler(EntityNotFoundException.class)
    protected ResponseEntity<Object> handleEntityNotFound(EntityNotFoundException ex) {
        ApiError apiError = new ApiError(NOT_FOUND);
        apiError.setMessage(ex.getMessage());
        return buildResponseEntity(apiError);
    }


    /**
     * Handle Exception, handle generic Exception.class
     *
     * @param ex
     *            the Exception
     * @return the ApiError object
     */
    @ExceptionHandler(MethodArgumentTypeMismatchException.class)
    protected ResponseEntity<Object> handleMethodArgumentTypeMismatch(MethodArgumentTypeMismatchException ex,
            WebRequest request) {
        ApiError apiError = new ApiError(BAD_REQUEST);
        apiError.setMessage(String.format("The parameter '%s' of value '%s' could not be converted to type '%s'",
                ex.getName(), ex.getValue(), ex.getRequiredType().getSimpleName()));
        apiError.setDebugMessage(ex.getMessage());
        return buildResponseEntity(apiError);
    }

    private ResponseEntity<Object> buildResponseEntity(ApiError apiError) {
        return new ResponseEntity<>(apiError, apiError.getStatus());
    }

}

But, when any exception occurs the application is redirected to /error page rather than being handled by the exception handler class. Can anyone advice on the right way of doing this.

Answer 1

Which exceptions are not been catch by the handler? Are the ConstraintViolationExceptions?

When you do:

@Valid @RequestBody User entity

You are firing the validation in the method, so if the constraints you use to decorate your User class are not fulfilled a MethodArgumentNotValidException will be thrown, not a ConstraintViolationException.

As you are extending ResponseEntityExceptionHandler you should check the code of such class which defines the following method:

@ExceptionHandler({
        HttpRequestMethodNotSupportedException.class,
        HttpMediaTypeNotSupportedException.class,
        HttpMediaTypeNotAcceptableException.class,
        MissingPathVariableException.class,
        MissingServletRequestParameterException.class,
        ServletRequestBindingException.class,
        ConversionNotSupportedException.class,
        TypeMismatchException.class,
        HttpMessageNotReadableException.class,
        HttpMessageNotWritableException.class,
        MethodArgumentNotValidException.class,
        MissingServletRequestPartException.class,
        BindException.class,
        NoHandlerFoundException.class,
        AsyncRequestTimeoutException.class
    })
@Nullable
public final ResponseEntity<Object> handleException(Exception ex, WebRequest request) throws Exception {
    HttpHeaders headers = new HttpHeaders();

    if (ex instanceof HttpRequestMethodNotSupportedException) {
        HttpStatus status = HttpStatus.METHOD_NOT_ALLOWED;
        return handleHttpRequestMethodNotSupported((HttpRequestMethodNotSupportedException) ex, headers, status, request);
    }
    else if (ex instanceof HttpMediaTypeNotSupportedException) {
        HttpStatus status = HttpStatus.UNSUPPORTED_MEDIA_TYPE;
        return handleHttpMediaTypeNotSupported((HttpMediaTypeNotSupportedException) ex, headers, status, request);
    }
    else if (ex instanceof HttpMediaTypeNotAcceptableException) {
        HttpStatus status = HttpStatus.NOT_ACCEPTABLE;
        return handleHttpMediaTypeNotAcceptable((HttpMediaTypeNotAcceptableException) ex, headers, status, request);
    }
    else if (ex instanceof MissingPathVariableException) {
        HttpStatus status = HttpStatus.INTERNAL_SERVER_ERROR;
        return handleMissingPathVariable((MissingPathVariableException) ex, headers, status, request);
    }
    else if (ex instanceof MissingServletRequestParameterException) {
        HttpStatus status = HttpStatus.BAD_REQUEST;
        return handleMissingServletRequestParameter((MissingServletRequestParameterException) ex, headers, status, request);
    }
    else if (ex instanceof ServletRequestBindingException) {
        HttpStatus status = HttpStatus.BAD_REQUEST;
        return handleServletRequestBindingException((ServletRequestBindingException) ex, headers, status, request);
    }
    else if (ex instanceof ConversionNotSupportedException) {
        HttpStatus status = HttpStatus.INTERNAL_SERVER_ERROR;
        return handleConversionNotSupported((ConversionNotSupportedException) ex, headers, status, request);
    }
    else if (ex instanceof TypeMismatchException) {
        HttpStatus status = HttpStatus.BAD_REQUEST;
        return handleTypeMismatch((TypeMismatchException) ex, headers, status, request);
    }
    else if (ex instanceof HttpMessageNotReadableException) {
        HttpStatus status = HttpStatus.BAD_REQUEST;
        return handleHttpMessageNotReadable((HttpMessageNotReadableException) ex, headers, status, request);
    }
    else if (ex instanceof HttpMessageNotWritableException) {
        HttpStatus status = HttpStatus.INTERNAL_SERVER_ERROR;
        return handleHttpMessageNotWritable((HttpMessageNotWritableException) ex, headers, status, request);
    }
    else if (ex instanceof MethodArgumentNotValidException) {
        HttpStatus status = HttpStatus.BAD_REQUEST;
        return handleMethodArgumentNotValid((MethodArgumentNotValidException) ex, headers, status, request);
    }
    else if (ex instanceof MissingServletRequestPartException) {
        HttpStatus status = HttpStatus.BAD_REQUEST;
        return handleMissingServletRequestPart((MissingServletRequestPartException) ex, headers, status, request);
    }
    else if (ex instanceof BindException) {
        HttpStatus status = HttpStatus.BAD_REQUEST;
        return handleBindException((BindException) ex, headers, status, request);
    }
    else if (ex instanceof NoHandlerFoundException) {
        HttpStatus status = HttpStatus.NOT_FOUND;
        return handleNoHandlerFoundException((NoHandlerFoundException) ex, headers, status, request);
    }
    else if (ex instanceof AsyncRequestTimeoutException) {
        HttpStatus status = HttpStatus.SERVICE_UNAVAILABLE;
        return handleAsyncRequestTimeoutException((AsyncRequestTimeoutException) ex, headers, status, request);
    }
    else {
        // Unknown exception, typically a wrapper with a common MVC exception as cause
        // (since @ExceptionHandler type declarations also match first-level causes):
        // We only deal with top-level MVC exceptions here, so let's rethrow the given
        // exception for further processing through the HandlerExceptionResolver chain.
        throw ex;
    }
}

So the MethodArgumentNotValidException is been catch here and the handling of such exception is pass to the handleMethodArgumentNotValid method.

The default handleMethodArgumentNotValid just call:

return handleExceptionInternal(ex, null, headers, status, request);

The better option here is to override handleMethodArgumentNotValid in RestExceptionHandler