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?

Slavin

I assume if you don't return anything, there will not be any content sent back? – Orgel

I think I'd still return a POJO of some sort, even if in Version 1 of your solution it just wraps a "success" boolean or something similar. Then you've got a consistent pattern in all your AJAX methods, and something that's easier to build on when it turns out you do need to return something! – Fondue

Contrary to what the answers are suggestion, what you first had in your second snippet is perfectly fine and the correct way to handle POST data. – Liquidate

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

Roundlet

Actually, you do not need to set @ResponseStatus and shouldn't. Simply having @ResponseBody on a void handler is fine enough. – Liquidate

I think it will be better to return a 204 No Content instead of a 200 for void methods – Jointure

@Jointure 200 is correct for POST as it's not meant to have a body. – Liquidate

@BrettRyan just as a comment, at least for a REST API it is a common practice that a POST will be used for creating content in which case it usually returns the id of the created enity(s), the full created entities or a link to the read operation. A 200 status return with no content could be confusing from a REST API perspective. – Jointure

@Roundlet If i am not using both (@ResponseBody AND @ResponseStatus(value = HttpStatus.OK)) the option then what would be happen??? – Mulligan

You can annotate @ResponseBody directly on the class. And if you annotate your class with @RestController, it contains already @ResponseBody. – Pericline

If your'e using thymeleaf and have a void endpoint, adding @ResponseStatus(value = HttpStatus.OK) fixed the Error resolving template [x/y/z] exception log. – Antiperiodic

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)
}

Insane

Incase anyone ran into the same problem I did, this didn't work on an older version of spring (4.1.1) I would get 500 errors. I upgraded to 4.2.0 and this works great – Lenticularis

That's my prefered way of returning empty 200 as well. Since Spring 4.1 use the builder pattern instead: return ResponseEntity.ok().build(); – Epochal

Although seems to compile, it gives the following warning ResponseEntity is a raw type. References to generic type ResponseEntity<T> should be parameterized – Batwing

I use ResponseEntity<?> as return type. No warnings, any response type can be returned – Ailsun

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.

Echo

setting @ResponseStatus(HttpStatus.NO_CONTENT) solved XML Parsing Error: no root element found for me in the browser – Snakemouth

Answer 4

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

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

Octant

so what will be the return type.. is it HTTP status code? – Keramic

@techBeginner In this case 200 (OK). – Meade

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.

Chomp

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).

Liquidate

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);
}

Blunge

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();
}

Pippa