我最近尝试开发一个servlet，然后将其连接到我的android应用程序，但我无法让它正常工作。

@WebServlet(name = "login", value = "/auth/login")
public class AuthUser extends HttpServlet {
    private Gson gson = new Gson();

    public void init() {
        Dao.registerDriver();
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        response.setContentType("application/json");
        response.setCharacterEncoding("UTF-8");
        String id = request.getParameter("id");
        String psw = request.getParameter("psw");

        HttpSession s = request.getSession();
        PrintWriter out = response.getWriter();

        HashMap<String, Object> responseJson = new HashMap<>();
        Student student;

        if(id != null && psw != null) {
            student = FetchFromDB.fetchStudentData(id);

            if (student != null && student.getPassword().equals(psw)) {
                s.setAttribute("username", student.getNumber());
                s.setAttribute("surname", student.getSurname());
                s.setAttribute("role", student.getRole());

                responseJson.put("id", request.getSession().getId());
                responseJson.put("user", student);
                responseJson.put("message", "Logged succesfully");
                out.print(new Gson().toJson(responseJson));
            } else {
                responseJson.put("message", "The mail or the username is not correct, please try again");
                out.println(new Gson().toJson(responseJson));
            }
        } else {
            responseJson.put("message", "The mail or username value is null, check that out");
        }
        out.flush();
    }

    public void destroy() {
    }
}

我在Android应用程序登录页面中调用此servlet，如下所示：

private void login() throws MalformedURLException {
        RequestQueue queue = Volley.newRequestQueue(this);
        String username = usernameText.getText().toString();
        String psw = passwordText.getText().toString();
        String url = Costants.URL + "auth/login?id="+username+"&psw="+psw+"";

        JsonObjectRequest jsonObjReq = new JsonObjectRequest(Request.Method.GET,
                url,
                null,
                response -> {

                    Log.d("In onResponse", ""+response);
                    try {
                        Log.d("In callServer", "Object returned: " +response.toString());
                        intent.putExtra("key-username", usernameText.getText().toString());
                        intent.putExtra("key-role", response.getJSONObject("user").getString("role"));
                        intent.putExtra("key-surname", response.getJSONObject("user").getString("surname"));
                        intent.putExtra("key-session-id", response.getString("id"));
                        startActivity(intent);
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }, error -> {
                    VolleyLog.d("In onErrorResponse", "Error: " + error.getMessage());
                    Toast.makeText(getApplicationContext(),
                            error.getMessage(), Toast.LENGTH_SHORT).show();
                });
        // Access the RequestQueue through your singleton class.

        MySingleton.getInstance(getApplicationContext()).addToRequestQueue(jsonObjReq);

    }

当我点击登录按钮时，它工作了，因此它与servlet通信，主活动正常启动。但是当我尝试从我的MainActivity进行另一个调用时，servlet中的会话将无法识别，因此用户显示为未知，以下是mainActivity的代码。

public class MainActivity extends AppCompatActivity {

    private ActivityMainBinding binding;
    String usernameOfLoggedUser;
    String surnameOfLoggedUser;
    String roleOfLoggedUser;
    String sessionId;
    Bundle extras;
    private UserViewModel viewModel;
    private BookedLessonsViewModel bookedLessonsViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        extras = getIntent().getExtras();
        usernameOfLoggedUser = extras.getString("key-username", "NoValue");
        surnameOfLoggedUser = extras.getString("key-surname", "NoValue");
        roleOfLoggedUser = extras.getString("key-role", "NoValue");
        sessionId = extras.getString("key-session-id", "NoValue");
        showWelcomeToast(usernameOfLoggedUser);
        setViewModelUser(usernameOfLoggedUser, roleOfLoggedUser, surnameOfLoggedUser);
        fetchBookedLessons(usernameOfLoggedUser);
        setupUIElements();
    }

    /**
     * Fetch lessons from db and set the model view for the lessons booked
     * @param username
     */
    private void fetchBookedLessons(String username) {
        String url = Costants.URL + "book/bookedLessonsForUser";
        ArrayList<BookedLesson> bookedLessons = new ArrayList<>();
        CustomRequest jsonCustomReq = new CustomRequest(
                Request.Method.GET,
                url,
                null,
                sessionId,
                new Response.Listener<JSONObject>() {
                    @Override
                    public void onResponse(JSONObject response) {
                            Log.d("in onResponse", response.toString());
//                        int i = 0;
//                        try {
//                            JSONArray reservations = response.getJSONArray("reservations");
//                            while(i < reservations.length()) {
//                                JSONObject reservation = reservations.getJSONObject(i);
//                                String idUser = reservation.getString("idUser");
//                                String idTeacher = reservation.getString("idTeacher");
//                                String subject = reservation.getString("nameSubject");
//                                String day = reservation.getString("day");
//                                String slot = reservation.getString("slot");
//                                String status =reservation.getString("status");
//
//                                BookedLesson bookedLesson = new BookedLesson(idUser, idTeacher, slot, subject, day, status);
//                                bookedLessons.add(bookedLesson);
//                                i++;
//                            }
//                        } catch (JSONException e) {
//                            e.printStackTrace();
//                        } finally {
//                            setViewModelLessons(bookedLessons);
//                        }
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {

                    }
                }
        );
        MySingleton.getInstance(getApplicationContext()).addToRequestQueue(jsonCustomReq);
    }

    private void showWelcomeToast(String username) {
        Toast toast = Toast.makeText(getApplicationContext(), "You are logged as: " + username, Toast.LENGTH_SHORT*2);
        toast.show();
    }

    @Override
    protected void onResume() {
        super.onResume();
        fetchBookedLessons(usernameOfLoggedUser);
    }

    private void setupUIElements() {
        binding = ActivityMainBinding.inflate(getLayoutInflater());
        setContentView(binding.getRoot());

        BottomNavigationView navView = findViewById(R.id.nav_view);
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(
                R.id.navigation_home, R.id.navigation_dashboard, R.id.navigation_notifications)
                .build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment_activity_main);
        NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);
        NavigationUI.setupWithNavController(binding.navView, navController);
    }

    /**
     * Set the model view for the user so that every fragment has the data for the logged user
     * @param usernameOfLoggedUser
     * @param roleOfLoggedUser
     * @param surnameOfLoggedUser
     */
    private void setViewModelUser(String usernameOfLoggedUser, String roleOfLoggedUser, String surnameOfLoggedUser) {
        viewModel = new ViewModelProvider(this).get(UserViewModel.class);

        viewModel.setUser(usernameOfLoggedUser);
        viewModel.setRole(roleOfLoggedUser);
        viewModel.setSurname(surnameOfLoggedUser);
        viewModel.getUser().observe(this, username -> {
            Log.d("In onCreate", "Share data: " + username);
        });
    }

    /**
     * Pass the array fetched and set the model view for the lessons
     * @param lessons
     */
    private void setViewModelLessons(ArrayList<BookedLesson> lessons) {
        bookedLessonsViewModel = new ViewModelProvider(this).get(BookedLessonsViewModel.class);

        bookedLessonsViewModel.setBookedLessons(lessons);

        bookedLessonsViewModel.getBookedLessons().observe(this, bookedLessons -> {
            Log.d("In getBookedLessons", "Lessons: " + bookedLessons.size());
        });
    }
}

但我得到的回报是这个值：

-26 13:48:47.053 12225-12225/com.example.bookinglessons D/in onResponse: {"message":"you're not logged"}

如果你知道发生了什么，这将是非常有帮助的，提前感谢。