php-不能从JSONObject中检索值

我通过PHP给android中的java类(Login screen)传递值，但是给出错误JSONException Error，不能从下面的代码中定义。请问如何修改呢？谢谢！

LoginActivity.java

@Overridepublic void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.login);    // Importing all assets like buttons, text fields    inputUid = (EditText) findViewById(R.id.loginUid);    inputPassword = (EditText) findViewById(R.id.loginPassword);    btnLogin = (Button) findViewById(R.id.btnLogin);    btnLinkToRegister = (Button) findViewById(R.id.btnLinkToRegisterScreen);    loginErrorMsg = (TextView) findViewById(R.id.login_error);    // Login button Click Event    btnLogin.setOnClickListener(new View.OnClickListener() {        public void onClick(View view) {            String id = inputUid.getText().toString();            String pswd = inputPassword.getText().toString();            UserFunctions userFunction = new UserFunctions();            Log.d("Button", "Login");            JSONObject json = userFunction.loginUser(id, pswd);            // check for login response            try {                if (json.getString(KEY_SUCCESS) != null) {                    loginErrorMsg.setText("");                    String res = json.getString(KEY_SUCCESS);                     if(Integer.parseInt(res) == 1){                        // user successfully logged in                        // Store user details in SQLite Database                        DatabaseHandler db = new DatabaseHandler(getApplicationContext());                        JSONObject json_user = json.getJSONObject("user");                        // Clear all previous data in database                        userFunction.logoutUser(getApplicationContext());                        db.addUser(json.getString(KEY_ID), json_user.getString(KEY_NAME), json_user.getString(KEY_EMAIL), json_user.getString(KEY_CREATED_AT));                                             // Launch Dashboard Screen                        Intent dashboard = new Intent(getApplicationContext(), DashboardActivity.class);                        // Close all views before launching Dashboard                        dashboard.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);                        startActivity(dashboard);                        // Close Login Screen                        finish();                    }else{                        // Error in login                        loginErrorMsg.setText("Incorrect username/password");                    }                }            } catch (JSONException e) {                e.printStackTrace();            }        }    });