How to return JSON object in resolveException method of HandlerExceptionResolver in Spring MVC?

Question

While implementing a File Uploader controller in Spring MVC I stucked with one problem. My code snap is given below.

@Controller
public class FileUploader extends AbstractBaseController implements HandlerExceptionResolver
{
    @RequestMapping(value = "/uploadFile", method = RequestMethod.POST)
    @ResponseBody
    public JSONObject handleFileUpload(@RequestParam("file") MultipartFile file)
    {
        JSONObject returnObj = new JSONObject();
        if (file.isEmpty())
        {
            returnObj.put("success", "false");
            returnObj.put("message", "File is empty");
        }
        else
        {
            try
            {
                //my file upload logic goes here 
            }
            catch (Exception e)
            {
                returnObj.put("success", "false");
                returnObj.put("message", "File not uploaded.");
            }
        }

        return returnObj;
    }

    @Override
    public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object obj, Exception exception)
    {
        ModelAndView model = new ModelAndView();
        Map map = new HashMap();
        if (exception instanceof MaxUploadSizeExceededException)
        {
            // I want to return JSONObject from here like given below.
            /**
             * { "message":"File size exceeded", "success":"false" }
             * */
            map.put("message", "File size exceeded");
            map.put("success", "false");
            model.addObject(map);
        }
        return model;
    }
}

and my spring configuration look likes

<bean id="multipartResolver"
    class="org.springframework.web.multipart.commons.CommonsMultipartResolver" >
    <property name="maxUploadSize" value="300000"/>
    </bean>

now In my controller I want to return JSONObject instead of ModelAndView in resolveException method in my controller as given in code snap because I am developing some like REST method to upload file.

any ideas? Thanks

Answer 1

You simply can annotate the method resolveException as @ExceptionHandler() and then you can have its signature like any other controller method. So placing @ResponseBody before the return type should work.

"Much like standard controller methods annotated with a @RequestMapping annotation, the method arguments and return values of @ExceptionHandler methods can be flexible. For example, the HttpServletRequest can be accessed in Servlet environments and the PortletRequest in Portlet environments. The return type can be a String, which is interpreted as a view name, a ModelAndView object, a ResponseEntity, or you can also add the @ResponseBody to have the method return value converted with message converters and written to the response stream."

Answer 2

If you use the Spring 3.2 above, I recommend this way.

1. At first, declare the ControllerAdvice.

   @Controller
   @ControllerAdvice
   public class JAttachfileApi extends BaseApi
   

2. And make the Exception Handler to response JSON Object as following.

       @ExceptionHandler(MaxUploadSizeExceededException.class)
       public @ResponseBody Map<String,Object> handleMaxUploadSizeExceededException(
    MaxUploadSizeExceededException ex) 
       {
   
           Map<String,Object> result = getResult();
   
           JFileUploadJsonResponse errorResult = new JFileUploadJsonResponse();
           errorResult.setError("Maximum upload size of "+ex.getMaxUploadSize()+" bytes exceeded.");
           List<JFileUploadJsonResponse> resultData = new ArrayList<JFileUploadJsonResponse>();
           resultData.add(errorResult);
           result.put("files", resultData);
   
         return result;
       }