Return null in ResponseEntity body (Spring Boot RESTful)

user_7020354 0
Viewed 25962

I'm creating a RESTFul Web Service with the following service available:

@RequestMapping(value = "/test", produces = "application/json", method = RequestMethod.GET)
public ResponseEntity<List<GenericModel>> returnEmpty() {
    List<GenericModel> genericModelList = new ArrayList<>();

    HttpHeaders headers = new HttpHeaders();
    headers.add("Content-Type", "application/json; charset=utf-8");

    return responseEntity = new ResponseEntity<>(genericModelList, headers, HttpStatus.OK);
}

When the empty list returns, I'm getting the following response in browser:

[]

How can I do to receive in browser a "null" response instead of []? There's some way to tell Spring to render my list size 0 as "null" and not as []?

spring-boot rest web-services spring java
3 Answers

One way of pivoting it based on if the genericModelList is empty of not could be:-

if(genericModelList.isEmpty()) {
    return new ResponseEntity<>(null, headers, HttpStatus.OK);
} else {
    return new ResponseEntity<>(genericModelList, headers, HttpStatus.OK);
}

or else you can skip the body using ResponseEntity(MultiValueMap<String,String> headers, HttpStatus status) constructor as well.

user_17461180

Because you just initialize the genericModelList as an empty list, not null. Or you can check the size of list before sending response back with different body.

user_64697720

Thanks everybody, I will try to be more clear next time. I solved the problem.

I was trying to send "null" in the body of my ResponseEntity> when my List size is 0, but Jackson creates a "[]" JSON and not a "null" as I wanted. I didn't found a way to change this default Jackson's bahavior, so I decided to abandon Jackson and use the Gson library.

Let me show a example of my solution:

@RequestMapping(value = "/test", produces = "application/json", method = RequestMethod.GET)
public ResponseEntity<String> returnEmpty() {

    List<GenericModel> genericModelList = new ArrayList<>();

    HttpHeaders headers = new HttpHeaders();
    headers.add("Content-Type", "application/json; charset=utf-8");

    String body = "";

    if (genericModelList.size() == 0) {
        body = "null";
    } else {
        body = gson.toJson(genericModelList);
    }

    return responseEntity = new ResponseEntity<>(body, headers, HttpStatus.OK);
}

This way, returning a String and parsing to JSON myself with Gson instead of use automatic parsing from Spring/Jackson, I can control the resulting JSON. Look that I explicity return a String "null" if my List.size() == 0.

user_70203540
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