Validation error handling catches the exception that Spring throws when validation fails and turns it into a clear, structured response.It is used so the client gets “which field failed and why” instead of a long default Spring error or a server error. It is done with a @RestControllerAdvice class containing @ExceptionHandler methods, so one place handles errors for all controllers. Every error comes back in the same JSON shape, with a status, a message and an errors map of field: message.
Features
- One global handler (
GlobalExceptionHandler) for all controllers, so there is no try/catch in the controller. - Field-level messages, for example
"age": "Age must be at least 18". - The same response format for every error.
- Handles several kinds of failure, not only
@Valid(see the table below). - Correct HTTP status codes: 400, 404, 409 and 500.
- The generic 500 handler hides internal details from the client.
Validation Error Handling Types
| Failure | Exception caught | Status | Example |
|---|---|---|---|
Body validation (@Valid @RequestBody) |
MethodArgumentNotValidException |
400 | Name too short, bad email |
Parameter validation (@RequestParam, @PathVariable) |
ConstraintViolationException |
400 | /students/by-age?age=5 |
| Unreadable or wrong-type JSON | HttpMessageNotReadableException |
400 | "age": "twenty", broken JSON |
| Wrong type or missing value in the URL | MethodArgumentTypeMismatchException, MissingServletRequestParameterException |
400 | /students/abc, no age param |
| Business-rule error (custom exception) | DuplicateEmailException |
409 | Email already registered |
| Resource not found (custom exception) | StudentNotFoundException |
404 | /students/99 |
| Unexpected error | Exception |
500 | Any bug, with a safe message |