java 中的 httpResponse returns 为空

Question

我正在尝试从我的服务器端获取对我的应用程序的响应，并且在我的 HTTP 响应中得到了 null。当我在浏览器中粘贴 URL 时，我得到了想要的响应。

URL：“http://localhost:8080/TBookServerSide/LoginServlet?u=admin&p=123”

响应：

{ "info" : "success" }

就像我得到一个 JSON 对象返回，在我的信息参数中包含成功一词但是，当我尝试使用 android 应用程序时，我得到的是 null。

我需要填写登录表单（用户名和密码），然后按登录按钮才能正常工作。

这是我的代码：

LoginFragment.java:

public class LoginFragment extends Fragment {
    public LoginFragment() {
        // Required empty public constructor
    }

    EditText firstNameText;
    EditText lastNameText;
    EditText userNameText;
    EditText passwordText;
    EditText emailText;

    Button loginButton;
    Button signUpPageButton;

    // Creating JSON Parser object
    com.example.liran.tbookandroid.LoginPage.JSONParser jParser = new com.example.liran.tbookandroid.LoginPage.JSONParser();


    private static String url_login = "http://localhost:8080/TBookServerSide/LoginServlet";
    //JSONArray incoming_msg = null;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
        View root = inflater.inflate(R.layout.fragment_login, container, false);

        (...)

        loginButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                User newUser = new User();
                String userName = userNameText.getText().toString();
                String password = passwordText.getText().toString();

                newUser.setUserName(userName);
                newUser.setPassword(password);

                Log.d("Press Button:","Login Button has been pressed");
                new LoginWithServlet(newUser).execute();
            }
        });

        return root;
    }

    private class LoginWithServlet extends AsyncTask<String, String, String> {
        JSONObject json;
        User user;
        boolean isUserExist = false;

        public LoginWithServlet(User user) {
            this.user = user;
        }

        @Override
        protected String doInBackground(String... params2) {
            // Getting username and password from user input
            String username = user.getUserName();
            String pass = user.getPassword();

            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("u", username));
            params.add(new BasicNameValuePair("p", pass));
            json = jParser.makeHttpRequest(url_login, "GET", params);
            String s = null;

            try {
                if (json != null) {
                    s = json.getString("info");
                    Log.d("Msg", json.getString("info"));
                    if (s.equals("success")) {
                        // SUCCEED LOGIN !!!!
                        Log.d("Login Servlet: "," Login Succeed");
                        ((MainActivity) getActivity()).openMainPageFragment();
                        ((MainActivity) getActivity()).showBarButtons();
                    } else {
                        // FAILED LOGIN
                        Log.d("Login Servlet: "," Login failed");
                    }
                } else {
                    Log.e("JSon:"," is NULL");
                }
            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            return null;
        }
    }

}

JSONParser.java

public class JSONParser {
    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";

    static InputStream iStream = null;
    static JSONArray jarray = null;
    //static String json = "";

    // constructor
    public JSONParser() {}

    // function get json from url
    // by making HTTP POST or GET mehtod
    public JSONObject makeHttpRequest(String url, String method, List<NameValuePair> params) {
        // Making HTTP request
        try {
            // check for request method
            if(method == "POST"){
                // request method is POST
                // defaultHttpClient
                DefaultHttpClient httpClient = new DefaultHttpClient();
                HttpPost httpPost = new HttpPost(url);
                httpPost.setEntity(new UrlEncodedFormEntity(params));

                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();
            } else if(method == "GET"){
                // request method is GET
                DefaultHttpClient httpClient = new DefaultHttpClient();
                String paramString = URLEncodedUtils.format(params, "utf-8");
                url += "?" + paramString;
                HttpGet httpGet = new HttpGet(url);

                HttpResponse httpResponse = httpClient.execute(httpGet);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();
            }

        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            json = sb.toString();
        } catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " + e.toString());
        }

        // try parse the string to a JSON object
        try {
            jObj = new JSONObject(json);
        } catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " + e.toString());
        }

        // return JSON String
        return jObj;

    }
}

LogCat:

com.example.liran.tbookandroid E/Buffer Error: Error converting result java.lang.NullPointerException: lock == null
com.example.liran.tbookandroid E/JSON Parser: Error parsing data org.json.JSONException: End of input at character 0 of 
com.example.liran.tbookandroid E/JSon::  is NULL

我不知道为什么它没有按预期工作，非常感谢你们的帮助。

Answer 1

http://localhost:8080/ 只能由您的计算机识别，因为它托管在该计算机上。此处，localhost 表示您配置服务器的计算机，因此您的浏览器能够 locate/find 它。

当您在移动设备上调用相同时，localhost 表示您的移动设备而不是您的计算机。这就是它不起作用的原因。

您仍然可以使用本地服务器进行开发。尝试连接 this.

Answer 2

如果你是运行 windows 查找计算机的 ip : 按 windows 键 + R 然后键入 CMD 然后键入 ipconfig 并按 enter

之后你可以在IPv4-Address前面看到你的IP地址

键入它而不是本地主机

Answer 3

你知道localhost的意思吗？它是你个人电脑的本地ip，所以你可以在你的浏览器中成功。

如果你只是想在你的 app.You 上做一个测试，应该在你的电脑上打开一个热点，然后让你的 android phone 连接上它。

或者像这样将本地 url 更改为外部 url：http://wthrcdn.etouch.cn/weather_mini?citykey=101010100

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