In this quick article, we will discuss one important Spring MVC interview question that is How to handle exceptions in Spring MVC applications?

How to Handle Exceptions in Spring MVC Applications?

We have three options for exceptions handling in Spring MVC:

• Using HTTP Status Codes
• Controller-Based Exception Handling (Using @ExceptionHandler)
• Global Exception Handling (Using @ExceptionHandler)

Using HTTP Status Codes

Normally any unhandled exception thrown when processing a web request causes the server to return an HTTP 500 response. However, any exception that you write yourself can be annotated with the @ResponseStatus annotation When an annotated exception is thrown from a controller method, and not handled elsewhere, it will automatically cause the appropriate HTTP response to be returned with the specified status code.

For example, here is an exception for a missing order.

@ResponseStatus(value=HttpStatus.NOT_FOUND, reason="No such Order")  // 404
 public class OrderNotFoundException extends RuntimeException {
     // ...
 }

And here is a controller method using it:

 @RequestMapping(value="/orders/{id}", method=GET)
 public String showOrder(@PathVariable("id") long id, Model model) {
     Order order = orderRepository.findOrderById(id);

     if (order == null) throw new OrderNotFoundException(id);

     model.addAttribute(order);
     return "orderDetail";
 }

A familiar HTTP 404 response will be returned if the URL handled by this method includes an unknown order id.

Controller-Based Exception Handling

Another way to handle the exceptions is by using the @ExceptionHandler annotation. We add @ExceptionHandler methods to any controller and use them to handle the exceptions thrown from inside that controller. 

@ExceptionHandler(ResourceNotFoundException.class)
public ResponseEntity<?> resourceNotFoundException(ResourceNotFoundException ex, WebRequest request) {
  ErrorDetails errorDetails = new ErrorDetails(new Date(), ex.getMessage(), request.getDescription(false));
  return new ResponseEntity<>(errorDetails, HttpStatus.NOT_FOUND);
}

Global Exception Handling

The third option for handling errors is by @ControllerAdvice classes. It'll allow us to apply the same techniques, only this time at the application level and not only to the particular controller. To enable this, we need to use the @ControllerAdvice and the @ExceptionHandler together. This way exception handlers will handle exceptions thrown by any controller.

For example:

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<?> resourceNotFoundException(ResourceNotFoundException ex, WebRequest request) {
        ErrorDetails errorDetails = new ErrorDetails(new Date(), ex.getMessage(), request.getDescription(false));
        return new ResponseEntity<>(errorDetails, HttpStatus.NOT_FOUND);
    }

    @ExceptionHandler(Exception.class)
    public ResponseEntity<?> globleExcpetionHandler(Exception ex, WebRequest request) {
        ErrorDetails errorDetails = new ErrorDetails(new Date(), ex.getMessage(), request.getDescription(false));
        return new ResponseEntity<>(errorDetails, HttpStatus.INTERNAL_SERVER_ERROR);
    }
}

Learn more about handling exceptions in Spring MVC or Spring boot applications at Spring Boot Exception Handling Example

References

Spring Boot Exception Handling Example