What to return if Spring MVC controller method doesn't return value?

Question

I am using jQuery's $.getJSON() to make asynchronous calls to my simple Spring MVC backend. Most of the Spring controller methods look like this:

@RequestMapping(value = "/someURL", method = RequestMethod.POST)
public @ResponseBody SomePOJO getSomeData(@ModelAttribute Widget widget,
    @RequestParam("type") String type) {
    return someDAO.getSomeData(widget, type);
}   

I have things set up so that each controller returns the @ResponseBody as JSON, which is what the client-side expects.

But what happens when a request isn't supposed to return any content to the client-side? Can I have:

@RequestMapping(value = "/updateSomeData" method = RequestMethod.POST)
public @ResponseBody void updateDataThatDoesntRequireClientToBeNotified(...) {
    ...
}

If not, what's the appropriate syntax to use here?

Answer 1

you can return void, then you have to mark the method with @ResponseStatus(value = HttpStatus.OK) you don't need @ResponseBody

@RequestMapping(value = "/updateSomeData" method = RequestMethod.POST)
@ResponseStatus(value = HttpStatus.OK)
public void updateDataThatDoesntRequireClientToBeNotified(...) {
    ...
}

Only get methods return a 200 status code implicity, all others you have do one of three things:

• Return void and mark the method with @ResponseStatus(value = HttpStatus.OK)
• Return An object and mark it with @ResponseBody
• Return an HttpEntity instance

Answer 2

You can simply return a ResponseEntity with the appropriate header:

@RequestMapping(value = "/updateSomeData" method = RequestMethod.POST)
public ResponseEntity updateDataThatDoesntRequireClientToBeNotified(...){
....
return new ResponseEntity(HttpStatus.OK)
}

Answer 3

You can return "ResponseEntity" object. Using "ResponseEntity" object is very convenient both at the time of constructing the response object (that contains Response Body and HTTP Status Code) and at the time of getting information out of the response object.

Methods like getHeaders(), getBody(), getContentType(), getStatusCode() etc makes the work of reading the ResponseEntity object very easy.

You should be using ResponseEntity object with a http status code of 204(No Content), which is specifically to specify that the request has been processed properly and the response body is intentionally blank. Using appropriate Status Codes to convey the right information is very important, especially if you are making an API that is going to be used by multiple client applications.

Answer 4

Yes, you can use @ResponseBody with void return type:

@RequestMapping(value = "/updateSomeData" method = RequestMethod.POST)
@ResponseBody
public void updateDataThatDoesntRequireClientToBeNotified(...) {
    ...
}

Answer 5

But as your system grows in size and functionality... i think that returning always a json is not a bad idea at all. Is more a architectural / "big scale design" matter.

You can think about returing always a JSON with two know fields : code and data. Where code is a numeric code specifying the success of the operation to be done and data is any aditional data related with the operation / service requested.

Come on, when we use a backend a service provider, any service can be checked to see if it worked well.

So i stick, to not let spring manage this, exposing hybrid returning operations (Some returns data other nothing...).. instaed make sure that your server expose a more homogeneous interface. Is more simple at the end of the day.

Answer 6

There is nothing wrong with returning a void @ResponseBody and you should for POST requests.

Use HTTP status codes to define errors within exception handler routines instead as others are mentioning success status. A normal method as you have will return a response code of 200 which is what you want, any exception handler can then return an error object and a different code (i.e. 500).

Answer 7

HttpStatus is required.

@ResponseStatus(value = HttpStatus.OK)
public void update(...) {
    ...
}

or ResponseEntity with null body and null header.

public ResponseEntity<Void> delete(@PathVariable Long id) {
    return new ResponseEntity<>(HttpStatus.NO_CONTENT);
}

Answer 8

You can use Void class:

The Void class is an uninstantiable placeholder class to hold a reference to the Class object representing the Java keyword void.

@GetMapping
public ResponseEntity<Void> method() {
   return ResponseEntity.status(HttpStatus.OK)
          .build();
}