Spring Boot 2.2.5 404 page not found custom json response - spring

Question

How can I have a custom json for my 404 pages ?
actually what I need is to be able to create custom json errors for my application.
for example for 404,401,403,422, ...
I searched a lot and what I found is :
package ir.darsineh.lms.http.exceptionHandler;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.servlet.NoHandlerFoundException;
import org.springframework.web.servlet.mvc.method.annotation.ResponseEntityExceptionHandler;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
#ControllerAdvice
public class CustomExceptionHandler extends ResponseEntityExceptionHandler {
#ExceptionHandler(NoHandlerFoundException.class)
public void springHandleNotFound(HttpServletResponse response) throws IOException {
response.sendError(HttpStatus.NOT_FOUND.value());
}
}
and here is the error I get :
Ambiguous #ExceptionHandler method mapped for [class org.springframework.web.servlet.NoHandlerFoundException]
I need my api response body json to be something like this :
{"code": 404, "message": "page not found"}

Answer 1

First, you should let Spring MVC to throw exception if no handler is found:
spring.mvc.throw-exception-if-no-handler-found=true
Then, the exception must be caught using a #ControllerAdvice:
#ControllerAdvice
public class CustomAdvice {
// 404
#ExceptionHandler({ NoHandlerFoundException.class })
#ResponseBody
#ResponseStatus(HttpStatus.NOT_FOUND)
public CustomResponse notFound(final NoHandlerFoundException ex) {
return new CustomResponse(HttpStatus.NOT_FOUND.value(), "page not found");
}
}
#Data
#AllArgsConstructor
class CustomResponse {
int code;
String message;
}
Do not forget to add #EnableWebMvc annotation to your app.

Answer 2

ResponseEntityExceptionHandler class already has handleNoHandlerFoundException() method defined as below.
protected ResponseEntity<Object> handleNoHandlerFoundException(NoHandlerFoundException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
return this.handleExceptionInternal(ex, (Object)null, headers, status, request);
}
Since the method signatures (parent class and our implementation class) are different, it resulted in ambiguous error. Using the same signature will override the above method with our custom implementation.
#ExceptionHandler(NoHandlerFoundException.class)
protected ResponseEntity<Object> handleNoHandlerFoundException(NoHandlerFoundException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
ErrorResponse error = new ErrorResponse("404", "page not found");
return new ResponseEntity(error, HttpStatus.NOT_FOUND);
}
Hope this helps!!