java - 为什么这段代码不能在 android 9 上正确运行？

Question

我有一个项目连接到 LAMP 服务器并使用 AsyncTask 获取一些数据。该应用程序可以在从 API 16 到 API 26 的所有 Android API 上正确运行。但是，当在 Android 9 (API 28) 上检查它时，在我在下面显示的代码中，变量“res”不会返回任何数据。 为什么？

import android.os.AsyncTask;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLEncoder;

public class loginserver extends AsyncTask {
    private String Link = "";
    private String User = "";
    private String Pass = "";

    public loginserver(String link, String user, String pass) {
        Link = link;
        User = user;
        Pass = pass;
    }

    @Override
    protected Object doInBackground(Object[] objects) {
        try {
            String data = URLEncoder.encode("username", "UTF8") +
                    "=" + URLEncoder.encode(User, "UTF8");
            data += "&" + URLEncoder.encode("password", "UTF8") +
                    "=" + URLEncoder.encode(Pass, "UTF8");
            URL url = new URL(Link);
            URLConnection urlConnection = url.openConnection();

            urlConnection.setDoOutput(true);
            OutputStreamWriter outputStreamWriter =
                    new OutputStreamWriter(urlConnection.getOutputStream());
            outputStreamWriter.write(data);
            outputStreamWriter.flush();

            BufferedReader bufferedReader =
                    new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
            StringBuilder stringBuilder = new StringBuilder();

            String line = null;
            while ((line = bufferedReader.readLine()) != null) {
                stringBuilder.append(line);
            }
            SecondActivity.res = stringBuilder.toString();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
}

Answer 1

考虑到 API 28 出了问题，我怀疑这与 this 有关。 。该链接指向一篇 Android 开发者博客文章，详细介绍了 Android P 上引入的与网络安全相关的限制，基本上禁止明文通信，除非您采取措施将某些域列入白名单。