使用AsyncTask从url读取txt，并在主线程中将其用作字符串

Question

我已经从URL读取了txt文件但是不能在主线程中使用从URL到字符串的读取文本。我有以下代码。

如何在主线程中从AsyncTask中读取字符串？

  package np.info.mukesh.utdlive;

/**
 * Created by Mukesh on 4/30/2017.
 */

import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.webkit.WebView;
import android.widget.MediaController;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.VideoView;

import com.google.android.gms.analytics.HitBuilders;
import com.google.android.gms.analytics.Tracker;
import com.thin.downloadmanager.util.Log;


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.Calendar;

public class LoadActivity extends AppCompatActivity {
    private Tracker mTracker;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_load);

        new GetMethodDemo().execute("http://m.live.mukesh.info.np/link.txt");

      //Toast data read from url
        Toast.makeText(this,server_response(), Toast.LENGTH_LONG).show();



    }



    public class GetMethodDemo extends AsyncTask<String , Void ,String> {
        String server_response;

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

            URL url;
            HttpURLConnection urlConnection = null;

            try {
                url = new URL(strings[0]);
                urlConnection = (HttpURLConnection) url.openConnection();

                int responseCode = urlConnection.getResponseCode();

                if(responseCode == HttpURLConnection.HTTP_OK){
                    server_response = readStream(urlConnection.getInputStream());
                    Log.v("CatalogClient", server_response);
                }

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

            return null;
        }

        @Override
        protected void onPostExecute(String s) {
            super.onPostExecute(s);


            TextView tv = (TextView) findViewById(R.id.updateNotice);
            tv.setText(server_response);

        }
    }


// Converting InputStream to String

    private String readStream(InputStream in) {
        BufferedReader reader = null;
        StringBuffer response = new StringBuffer();
        try {
            reader = new BufferedReader(new InputStreamReader(in));
            String line = "";
            while ((line = reader.readLine()) != null) {
                response.append(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return response.toString();
    }



}

我一直在寻找解决方案好几天但没有运气。我正在从stackoverflow和google以及一些博客文章中学习android。所以，我没有多少经验。谢谢！