我在Java上有一个restlet项目。我无法解析JSON对象。我该怎么办？

Question

public static void runClient() throws JSONException {

    String httpServerHostAddr = "127.0.0.1";
    int httpServerPort = Constants.HTTP_SERVER_PORT;

    ProductResource clientHandle = ClientResource.create(
            "http://" + httpServerHostAddr + ":" + httpServerPort + "/student", ProductResource.class);

    StudentDTO student = new StudentDTO();
    System.out.println("TEST Starting\n");
    student.setStudentNo("123456789");
    student.setName("Jhon");
    student.setSurname("Gibson");
    student.setIdentityNumber("15423200");
    student.setSex(Byte.valueOf("0"));
    student.setFacultyId(Byte.valueOf("1"));
    student.setDepartmentId(Byte.valueOf("2"));

    JsonRepresentation jsonRep = student.toJsonRepresentation();
    JsonRepresentation response = (JsonRepresentation) clientHandle.store(jsonRep);
    StudentDTO responseStudent = new StudentDTO(response);
    System.out.println("What's Stored: " + responseStudent.toString());

    ProductResource clientHandle2 = ClientResource.create(
            "http://" + httpServerHostAddr + ":" + httpServerPort + "/student/" 
                    + responseStudent.getStudentId(), ProductResource.class);

    response = (JsonRepresentation) clientHandle2.represent();
    responseStudent = new StudentDTO(response);
    System.out.println("\nWhat's retrieved: " + responseStudent.toString());

以上代码是我测试项目的主要代码

@Override
public JsonRepresentation toJsonRepresentation() throws SystemException {
    try {
        JSONObject jsonObjectRep = new JSONObject();
        if (this.getExitCode() == Constants.EXIT_SUCCESS) {
            jsonObjectRep.put("studentId", this.getStudentId());
            jsonObjectRep.put("studentNo", this.getStudentNo());
            jsonObjectRep.put("name", this.getName());
            jsonObjectRep.put("surname", this.getSurname());
            jsonObjectRep.put("identityNumber", this.getIdentityNumber());
            jsonObjectRep.put("birthDate",this.getBirthDate());
            jsonObjectRep.put("sex", this.getSex());
            jsonObjectRep.put("facultyId", this.getFacultyId());
            jsonObjectRep.put("departmentId", this.getDepartmentId());
            jsonObjectRep.put("educationYear", this.getEducationYear());
            jsonObjectRep.put("educationStatus", this.getEducationStatus());
            jsonObjectRep.put("macAdress", this.getMacAdress());
            jsonObjectRep.put("exitCode", this.getExitCode());
        } else {
            jsonObjectRep.put("exitCode", this.getExitCode());
        }
        JsonRepresentation jsonRep = new JsonRepresentation(jsonObjectRep);
        return jsonRep;
    } catch (JSONException ex) {
        SystemException e = SystemException.wrap(ex, ValidationCode.UNABLE_TO_PRODUCE_JSON_REPRESENTATION);
        throw e;
    }
}

上面的代码片段显示了我如何创建我的JSON对象

 @Override
protected void fromJsonRepresentation(JsonRepresentation json) throws SystemException {
    try {
        JSONObject jsonObj;
        jsonObj = json.getJsonObject();
        this.studentId = jsonObj.getInt("studentId");
        this.studentNo = jsonObj.getString("studentNo");
        this.name = jsonObj.getString("name");
        this.surname = jsonObj.getString("surname");
        this.identityNumber = jsonObj.getString("identityNumber");
        try {
            this.birthdate = sFormat.parse(jsonObj.getString("birthDate"));
        } catch (ParseException ex) {
            Logger.getLogger(StudentDTO.class.getName()).log(Level.SEVERE, null, ex);
        }
        this.sex = (byte) jsonObj.getInt("sex");
        this.facultyId = (byte) jsonObj.getInt("facultyId");
        this.departmentId = (byte) jsonObj.getInt("departmentId");
        this.educationYear = (byte) jsonObj.getInt("educationYear");
        this.educationStatus = (byte) jsonObj.getInt("educationStatus");
        this.macAdress = jsonObj.getString("macAdress");
        this.setExitCode(jsonObj.getInt("exitCode"));
    } catch (JSONException ex) {
        SystemException e = SystemException.wrap(ex, ValidationCode.UNABLE_TO_PARSE_JSON);
        throw e;
    }
}

这就是我在尝试解析代码中的JSON对象。我收到此错误org.json.JSONException: JSONObject["studentId"] not found.