How to return JSON object to AngularJS using Java Servlet

Question

I have to write a controller in my project using servlets. I've done it before but I've never worked with AngularJS, so I did it via request.setAttribute() and request.getParameter() and put Java code inside of a JSP page. But now frontend developer used AngularJS and I have to return him a JSON object. And I have no idea how to do it. Here's the code of abTestCtrl.js:

app.controller("abTestCtrl", function($scope, $location, $http) {
        $scope.title = "no title";
        $scope.description = "no description";
    $scope.getParam = $location.search()['id'];
    if($scope.getParam === undefined)$scope.getParam = 0; 

    //$scope.getParam=2;
    //path: localhost8080/UIUM.../servlet-name.java
        //with two ids
        //web.xml: serverlet mapping for the path
        if($scope.getParam==='0'||$scope.getParam === 0){
            var saveButton = document.getElementById("saveButton");
            saveButton.classList.remove("hidden");
        }
        else{
            $http.get('http://localhost:8080/UIUM_IMT4003/ABTestController', {command:'getTestCaseInfo', testcaseID:$scope.getParam}).
            success(function(data, status, headers, config) {
              // this callback will be called asynchronously
              // when the response is available
              console.log('request succesful');
              console.log(data);
              console.log(status);
              console.log(headers);
              console.log(config);
            }).
            error(function(data, status, headers, config) {
              // called asynchronously if an error occurs
              // or server returns response with an error status.
              console.log('request not succesful');
            });
        }

and my processRequest() code from the servlet:

protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException, SQLException, ClassNotFoundException {
        response.setStatus(HttpServletResponse.SC_OK);
        response.setContentType("application/json; charset=UTF-8");
        //PrintWriter printout = response.getWriter();

        JSONObject jObject = null;
        RequestDispatcher view = null;
        TestcaseRepository testcaseRepo = new TestcaseRepository();

        String command = request.getParameter("command");

        if(command == null)
        {
            view = request.getRequestDispatcher("/testcases.jsp");
            view.forward(request, response);
        }

        if(command.equals("getTestCaseInfo")){
            String testcaseId = request.getParameter("testcaseID");
            Testcase testcase = testcaseRepo.getTestcaseById(testcaseId);
            jObject = new JSONObject();
            jObject.put("id", testcaseId);
            jObject.put("title", testcase.getTestcaseName());
            jObject.put("testscenario", testcase.getTestcaseDescription());
//            printout.print(jObject);
//            printout.flush();
            jObject.write(response.getWriter());
        }       

Can you please help me to process this request and finally return this poor JSON!

BTW, Servlet doesn't recognize command parameter. It gets null. But there is such parameter in AngularJS function.

Solution

Try using the javax.json.JsonObject as follow:

JsonObject jo=Json.createObjectBuilder()
            .add("id", testcaseId)
            .add("title", testcase.getTestcaseName())
            .add("testscenario", testcase.getTestcaseDescription()).build();

Then set the response content type to json and send your json object in the response:

response.setContentType("application/json");// set content to json
PrintWriter out = response.getWriter();
out.print(jo);
out.flush();