从NPM JSON获取数据-服务器抛出NetworkOnMainThreadException

Question

Im编写了一个小的Android应用程序，它应该从npm JSON服务器获取数据。它会抛出一个异常。我确实使用AsyncTask扩展了connection类，并在“DoInBackground”中执行了代码，但它仍然抛出了一个异常。请帮帮我.

代码如下：

import android.os.AsyncTask;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class Network extends AsyncTask <String, Void, String> {
    public String urlString = ("http://localhost:3000");

    @Override
    protected String doInBackground(String... params) {
        StringBuffer chaine = new StringBuffer("");
        try {
            URL url = new URL(urlString);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestProperty("User-Agnet", "");
            connection.setRequestMethod("POST");
            connection.setDoInput(true);
            connection.connect();

            InputStream inputStream = connection.getInputStream();

            BufferedReader rd = new BufferedReader(new InputStreamReader(inputStream));
            String line = "";
            while ((line = rd.readLine()) != null) {
                chaine.append(line);
            }

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

        }
        return chaine.toString();
    }
}

logcat告诉我们：

Answer 1

    public class Network extends AsyncTask <String, Void, String> {
    public String urlString = ("http://localhost:3000");
    HttpURLConnection connection;
    URL url;
    StringBuffer chaine;

    @Override
    protected String doInBackground(String... params) {

    Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                chaine = new StringBuffer("");
        try {
            url = new URL(urlString);
            connection = (HttpURLConnection) url.openConnection();
            connection.setRequestProperty("User-Agnet", "");
            connection.setRequestMethod("POST");
            connection.setDoInput(true);
            connection.connect();

            InputStream inputStream = connection.getInputStream();

            BufferedReader rd = new BufferedReader(new       InputStreamReader(inputStream));
            String line = "";
            while ((line = rd.readLine()) != null) {
                chaine.append(line);
            }

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

        }
            }
        });
        thread.start();

        return chaine.toString();
    }
}