Android Android Server

I use the following code to make an Android device a file server (Android internal storage). I get an exception os.android.NetworkOnMainThread. I tried to put the onStart code in AsyncTask, but the application never starts and never starts when it starts. Any help regarding the ftp server on Android would be great as I don't know how to make it work.

Here is the code MainActivity

package com.googlecode.simpleftp;

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import android.app.Activity;
import android.app.AlertDialog;
import android.app.Dialog;
import android.content.Context;
import android.content.DialogInterface;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.TextView;
import android.widget.Toast;


public class FTPServer extends Activity {
    private static int COMMAND_PORT = 2121;
    static final int DIALOG_ALERT_ID = 0;
    private static ExecutorService executor  = Executors.newCachedThreadPool();

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
}

@Override
    public boolean onCreateOptionsMenu(Menu menu) {
            MenuInflater inflater = getMenuInflater();
            inflater.inflate(R.menu.my_menu, menu);
            return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {    
            // Handle item selection    
            switch (item.getItemId()) {
                    case R.id.new_game:    
                            System.out.println("New game button is pressed!");
                            //newGame();        
                            return true;    
                    case R.id.quit:        
                            System.out.println("Quit button is pressed!");
                            showDialog(DIALOG_ALERT_ID);        
                            return true;    
                    default:        
                            return super.onOptionsItemSelected(item);    }
    }

    @Override
    protected Dialog onCreateDialog(int id){
            AlertDialog.Builder builder = new AlertDialog.Builder(this);
            builder.setMessage("Are you sure you want to exit?")
            .setCancelable(false).setPositiveButton("yes", new DialogInterface.OnClickListener(){
                    @Override
                    public void onClick(DialogInterface dialog, int id){
                            FTPServer.this.finish();
                    }
            })
            .setNegativeButton("No", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                            dialog.cancel();

                    }
            });
            AlertDialog alert = builder.create();
            return alert;
    }

HEre is ServerPI Code

 import java.io.BufferedReader;
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.io.PrintWriter;
 import java.net.Socket;

 public class ServerPI implements Runnable{
    private Socket clientSocket;
    private BufferedReader in;
    private PrintWriter out;

    private String baseDir;
    private String relativeDir;
    private String absoluteDir;
    private String fileName;
    private String filePath;

    public ServerPI(Socket incoming) throws IOException{
            this.clientSocket = incoming;
            in = new BufferedReader(new InputStreamReader(this.clientSocket.getInputStream()));
            out = new PrintWriter(this.clientSocket.getOutputStream(), true);

            baseDir = new File("").getAbsolutePath();

            relativeDir = "/";
            absoluteDir = baseDir + relativeDir;
            fileName = "";
            filePath = absoluteDir + "/" + fileName;
    }

    private void readCommandLoop() throws IOException {
            String line = null;
            reply(220, "Welcome to the SimpleFTP server!");
            while((line = in.readLine()) != null){
                    int replyCode = executeCommand(line.trim());
                    if(replyCode == 221){
                            return;
                    }
            }
    }

    private int executeCommand(String trim) {
            // TODO Auto-generated method stub
            return 0;
    }

    public int reply(int statusCode, String statusMessage){
            out.println(statusCode + " " + statusMessage);
            return statusCode;
    }

    @Override
    public void run(){
            try{
                    this.readCommandLoop();
            } catch (IOException e){
                    e.printStackTrace();
            }
            finally {
                    try {
                            if(in != null){
                                    in.close();
                                    in = null;
                            }
                            if(out != null){
                                    out.close();
                                    out = null;
                            }
                            if (clientSocket != null){
                                    clientSocket.close();
                                    clientSocket = null;
                            }
                    }
                    catch (IOException e){
                            e.printStackTrace();
                    }
            }
    }
    }

I put the code in AsyncTask, here it is

   private class LongOperation extends AsyncTask<String, Void, String> {

      @Override
      protected String doInBackground(String... params) {
           ServerSocket s = null;
    Socket incoming = null;

    try{
            s = new ServerSocket(COMMAND_PORT);
            String ip = (s.getInetAddress()).getHostAddress();
            Context context = this.getApplicationContext();
            CharSequence text = ip;
            int duration = Toast.LENGTH_LONG;

            Toast toast = Toast.makeText(context, text, duration);
            Thread.sleep(1000);
            toast.show();
            while(true){
                    incoming = s.accept();
                    executor.execute(new ServerPI(incoming));
            }
    }
    catch(Exception e){
            System.out.println(e.toString());
            e.printStackTrace();
    }
    finally{
            try
                    {
                            if(incoming != null)incoming.close();
                    }
                    catch(IOException ignore)
                    {
                            //ignore
                    }

                    try
                    {
                            if (s!= null)
                            {
                                    s.close();
                            }
                    }
                    catch(IOException ignore)
                    {
                            //ignore
                    }
    }

            return "Executed";
      }      

      @Override
      protected void onPostExecute(String result) {               
      }

      @Override
      protected void onPreExecute() {
      }

      @Override
      protected void onProgressUpdate(Void... values) {
      }
}

Iam calls longOpertation in the onCreate method. What is the problem with the arrival of the application at startup.

  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_fullscreen);
            new LongOperation().execute();
    }