Spring boot - taking control of 404 Not Found

Question

I'm trying to figure out the simplest way to take control over the 404 Not Found handler of a basic Spring Boot RESTful service such as the example provided by Spring:

https://spring.io/guides/gs/rest-service/

Rather than have it return the default Json output:

{
  "timestamp":1432047177086,
  "status":404,
  "error":"Not Found",
  "exception":"org.springframework.web.servlet.NoHandlerFoundException",
  "message":"No handler found for GET /aaa, ..."
}

I'd like to provide my own Json output.

By taking control of the DispatcherServlet and using DispatcherServlet#setThrowExceptionIfNoHandlerFound(true), I was able to make it throw an exception in case of a 404 but I can't handle that exception through a @ExceptionHandler, like I would for a MissingServletRequestParameterException. Any idea why?

Or is there a better approach than having a NoHandlerFoundException thrown and handled?

Answer 1

It works perfectly Fine.

When you are using SpringBoot, it does not handle (404 Not Found) explicitly; it uses WebMvc error response. If your Spring Boot should handle that exception, then you should do some hack around Spring Boot. For 404, the exception class is NoHandlerFoundException; if you want to handle that exception in your @RestControllerAdvice class, you must add @EnableWebMvc annotation in your Application class and set setThrowExceptionIfNoHandlerFound(true); in DispatcherServlet. Please refer to the following code:

@SpringBootApplication
@EnableWebMvc
public class Application {  
    @Autowired
    private DispatcherServlet servlet;

    public static void main(String[] args) throws FileNotFoundException, IOException {
        SpringApplication.run(Application.class, args);
    }
    
    @Bean
    public CommandLineRunner getCommandLineRunner(ApplicationContext context) {
        servlet.setThrowExceptionIfNoHandlerFound(true);
        return args -> {};
    }
}

After this you can handle NoHandlerException in your @RestControllerAdvice class

@RestControllerAdvice
public class AppException {

    @ExceptionHandler(value={NoHandlerFoundException.class})
    @ResponseStatus(code=HttpStatus.BAD_REQUEST)
    public ApiError badRequest(Exception e, HttpServletRequest request, HttpServletResponse response) {
        e.printStackTrace();
        return new ApiError(400, HttpStatus.BAD_REQUEST.getReasonPhrase());
    }
}   

I have created ApiError class to return customized error response

public class ApiError {
    private int code;
    private String message;
    public ApiError(int code, String message) {
        this.code = code;
        this.message = message;
    }
    public ApiError() {
    }   
    //getter & setter methods...
}