RequestBody 在控制器中为空

Question

I'm trying to send JSON object from frontend to backend via jQuery AJAX. The ajax call is performed successfully on the requested path "/survey" with a POST method. Problem is, my @RequestBody final HmmSurveyForm hmmSurveyForm has null values for my fields "answer1" and "heading". When I checked request in google chrome developer request is sent:

But the response is null for populated fields from frontend:

I have following code in frontend:

postSurvey: function() {
        $.ajax({
            url: this.encodedContextPath + "/survey",
            type: 'POST',
            dataType: 'json',
            contentType: 'application/json',
            data: ACC.hmmSurvey.getJSONDataForSurvey(),
            async: true,
            success: function (response) {
                console.log(response);
            },
            error: function (jqXHR, textStatus, errorThrown) {
                console.log("The following error occurred: " + textStatus, errorThrown);
            }
        });
}

getJSONDataForSurvey: function () {
        var json = [];

        json.push({"answer1": "1"});
        json.push({"heading": "Test"});

        return JSON.stringify({"hmmSurveyForm": json});
}

and in backend:

@RequestMapping(value = "/survey", method = RequestMethod.POST, produces = MediaType.APPLICATION_JSON_VALUE)
public @ResponseBody HmmSurveyForm postSurvey(@RequestBody final HmmSurveyForm hmmSurveyForm, final Model model) {
    System.out.println(hmmSurveyForm);
    return hmmSurveyForm;
}

public class HmmSurveyForm {

    private String heading;
    private String answer1;

    // getter, setters
}

Answer 1

You are declaring your RQ body incorrectly in JS

 var json = []; json.push({"answer1": "1"}); json.push({"heading": "Test"}); console.log({"hmmSurveyForm": json});

which has the root hmmSurveyForm as an array of distinct objects, which has no relation to what your backend expects.

You should be using the code below;

 var json = {}; json["answer1"] = "1"; json["heading"] = "Test"; console.log({"hmmSurveyForm": json});

Check more on JSON Object in JS here