import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.InputStreamReader;

import java.io.OutputStreamWriter;

import java.io.PrintWriter;

import java.net.ServerSocket;

import java.net.Socket;

public class TCPServer implements Runnable {

    public static final int ServerPort = 9999;

    public static final String ServerIP = "xxx.xxx.xxx.xxxx";

    @Override

    public void run() {

        // TODO Auto-generated method stub

        try {

            System.out.println("S: Connecting...");

            ServerSocket serverSocket = new ServerSocket(ServerPort);

            while (true) {

                Socket client = serverSocket.accept();

                System.out.println("S: Receiving...");

                try {

                    BufferedReader in = new BufferedReader(

                    new InputStreamReader(client.getInputStream()));

                    String str = in.readLine();

                    System.out.println("S: Received: '" + str + "'");

                    PrintWriter out = new PrintWriter(new BufferedWriter(

                    new OutputStreamWriter(client.getOutputStream())),true);

                    out.println("Server Received " + str);

                } catch (Exception e) {

                    System.out.println("S: Error");

                    e.printStackTrace();

                } finally {

                    client.close();

                    System.out.println("S: Done.");

                }

            }

        } catch (Exception e) {

            System.out.println("S: Error");

            e.printStackTrace();

        }

    }

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        Thread desktopServerThread = new Thread(new TCPServer());

        desktopServerThread.start();

    }

}

package socket.client;

import java.io.BufferedInputStream;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.OutputStreamWriter;

import java.io.PrintWriter;

import java.net.Socket;

import java.net.URL;

import java.net.URLConnection;

import org.apache.http.util.ByteArrayBuffer;

import android.app.Activity;

import android.os.Bundle;

import android.os.Handler;

import android.util.Log;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.EditText;

import android.widget.TextView;

import android.widget.Toast;

public class NewClient extends Activity {

    private String html = "";

    private Handler mHandler;

    private Socket socket;

    private String name;

    private BufferedReader networkReader;

    private BufferedWriter networkWriter;

    private String ip = "xxx.xxx.xxx.xxx"; // IP

    private int port = 9999; // PORT번호

    @Override

    protected void onStop() {

        // TODO Auto-generated method stub

        super.onStop();

        try {

            socket.close();

        } catch (IOException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

    }

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        mHandler = new Handler();

        try {

            setSocket(ip, port);

        } catch (IOException e1) {

            // TODO Auto-generated catch block

            e1.printStackTrace();

        }

        checkUpdate.start();

        final EditText et = (EditText) findViewById(R.id.EditText01);

        Button btn = (Button) findViewById(R.id.Button01);

        final TextView tv = (TextView) findViewById(R.id.TextView01);

        btn.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {

                if (et.getText().toString() != null

                        || !et.getText().toString().equals("")) {

                    PrintWriter out = new PrintWriter(networkWriter, true);

                    String return_msg = et.getText().toString();

                    out.println(return_msg);

                }

            }

        });

    }

    private Thread checkUpdate = new Thread() {

        public void run() {

            try {

                String line;

                Log.w("ChattingStart", "Start Thread");

                while (true) {

                    Log.w("Chatting is running", "chatting is running");

                    line = networkReader.readLine();

                    html = line;

                    mHandler.post(showUpdate);

                }

            } catch (Exception e) {

            }

        }

    };

    private Runnable showUpdate = new Runnable() {

        public void run() {

            Toast.makeText(NewClient.this, "Coming word: " + html,

                    Toast.LENGTH_SHORT).show();

        }

    };

    public void setSocket(String ip, int port) throws IOException {

        try {

            socket = new Socket(ip, port);

            networkWriter =

new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));

            networkReader =

new BufferedReader(new InputStreamReader(socket.getInputStream()));

        } catch (IOException e) {

            System.out.println(e);

            e.printStackTrace();

        }

    }

}

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:orientation="vertical"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent" >

    <TextView android:id="@+id/TextView01"

    android:layout_height="wrap_content"

    android:layout_width="fill_parent"/>

    <EditText android:id="@+id/EditText01"

    android:layout_height="wrap_content"

    android:layout_width="fill_parent"/>

    <Button android:id="@+id/Button01"

    android:layout_width="wrap_content"

    android:layout_height="wrap_content"

    android:text="Send"/>

    <TextView android:id="@+id/chatting"

    android:layout_height="wrap_content"

    android:layout_width="fill_parent"/>   

</LinearLayout>

AndroidManifest.xml 에 추가해야할 인터넷 사용 허가권

<uses-permission android:name="android.permission.INTERNET" />

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

package="socket.client"

  android:versionCode="1"

  android:versionName="1.0">

   <application android:icon="@drawable/icon" android:label="@string/app_name">

      <activity android:name=".NewClient"

        android:label="@string/app_name">

    <intent-filter>

      <action android:name="android.intent.action.MAIN" />

      <category android:name="android.intent.category.LAUNCHER" />

    </intent-filter>

  </activity>

  </application>

   <uses-permission android:name="android.permission.INTERNET" />

</manifest>