Optional returned from controllers method
If you need to show 404 error page when no object found in your backend you can think of returning Optional from the controller's method and may expect Spring MVC takes care of exposing the value if present and throws 404 if empty.
Solution
The mechanism of controller advice comes to play. We can create a class that will be used to modify controller responses.
There are actually two features used:
- @ExceptionHandler which is used for translation exceptions into 404 error response
- ResponseBodyAdvice interface which cause body will be processed before been returned from controller endpoint.
Here you are piece of code that should gather above mentioned into one universal class
@ControllerAdvice
public class OptionalResponseControllerAdvice implements ResponseBodyAdvice {
@Override
public boolean supports(MethodParameter returnType, Class converterType) {
return returnType.getParameterType().equals(Optional.class);
}
@Override
public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType,
Class selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
if (returnType.getParameterType().equals(Optional.class)) {
return ((Optional<?>) body).orElseThrow(() -> new NotFoundException("No object found: " + request.getURI()));
}
return body;
}
@ExceptionHandler(UnauthorizedException.class)
public ResponseEntity<Map<String, Serializable>> handle(NotFoundException e) {
return ResponseEntity.status(HttpStatus.NOT_FOUND).body(e.getMessage());
}
}