Global exception handling

 If we write exception handler into the controller then we can not re-use it . Then need to write again which will violate co-usability rule.

So, to avoid code duplication we can define global exception handler using @ControllerAdvice.

@ControllerAdvice:

--Its similar to pre-processor/filter.

--Pre process request to controller.

-- Preprocess responses to handle exception.

--Perfect for global exception handling.

let's refactor our previous exception handling code-

@ControllerAdvice

public class StudentRestHandlerException{

@ExceptionHandler

public ResponseEntity<StudentErrorResponse> handleException(StudentNotFound  exc){

StudentErrorResponse errorResponse = new StudentErrorResponse();

errorResponse.setStatus(HttpStatus.Not_found.value());

errorResponse.setMessage(exc.getMessage());

errorResponse.setTimeStamp(System.currentTimeMillis());

return new ResponseEntity<>(errorResponse, HttpStatus.NOT_FOUND);// will return a json .jackson                                                                                                                           will convert the pojo to json .

}

What if the user request using character in request parameter without giving integer value . then server again will show an ugly message .so we should handle it . so lets create another exception handler ..

@ExceptionHandler

public ResponseEntity<StudentErrorResponse> handleException(Exception ex){

StudentErrorResponse errorResponse = new StudentErrorResponse();

errorResponse.setStatus(HttpStatus.BAD_REQUEST.value());

errorResponse.setMessage(exc.getMessage());

errorResponse.setTimeStamp(System.currentTimeMillis());

return new ResponseEntity<>(errorResponse, HttpStatus.BAD_REQUEST);

}

}