import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class Main {
  private static final int PORT = 9999;
  private List<Socket> mList = new ArrayList<Socket>();
  private ServerSocket server = null;
  private ExecutorService mExecutorService = null; //thread pool
  public static void main(String[] args) {
    new Main();
  }
  public Main() {
    try {
      server = new ServerSocket(PORT);
      mExecutorService = Executors.newCachedThreadPool(); //create a thread pool
      System.out.println("服务器已启动...");
      Socket client = null;
      while(true) {
        client = server.accept();
        //把客户端放入客户端集合中
        mList.add(client);
        mExecutorService.execute(new Service(client)); //start a new thread to handle the connection
      }
    }catch (Exception e) {
      e.printStackTrace();
    }
  }
  class Service implements Runnable {
      private Socket socket;
      private BufferedReader in = null;
      private String msg = "";
      public Service(Socket socket) {
        this.socket = socket;
        try {
          in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
          //客户端只要一连到服务器，便向客户端发送下面的信息。
          msg = "服务器地址：" +this.socket.getInetAddress() + "come toal:"
            +mList.size()+"（服务器发送）";
          this.sendmsg();
        } catch (IOException e) {
          e.printStackTrace();
        }
      }
      @Override
      public void run() {
        try {
          while(true) {
            if((msg = in.readLine())!= null) {
              //当客户端发送的信息为：exit时，关闭连接
              if(msg.equals("exit")) {
                System.out.println("ssssssss");
                mList.remove(socket);
                in.close();
                msg = "user:" + socket.getInetAddress()
                  + "exit total:" + mList.size();
                socket.close();
                this.sendmsg();
                break;
                //接收客户端发过来的信息msg，然后发送给客户端。
              } else {
                msg = socket.getInetAddress() + ":" + msg+"（服务器发送）";
                this.sendmsg();
              }
            }
          }
        } catch (Exception e) {
          e.printStackTrace();
        }
      }
     /**
      * 循环遍历客户端集合，给每个客户端都发送信息。
      */
      public void sendmsg() {
        System.out.println(msg);
        int num =mList.size();
        for (int index = 0; index < num; index ++) {
          Socket mSocket = mList.get(index);
          PrintWriter pout = null;
          try {
            pout = new PrintWriter(new BufferedWriter(
                new OutputStreamWriter(mSocket.getOutputStream())),true);
            pout.println(msg);
          }catch (IOException e) {
            e.printStackTrace();
          }
        }
      }
    }
}

package com.amaker.socket;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class SocketDemo extends Activity implements Runnable {
  private TextView tv_msg = null;
  private EditText ed_msg = null;
  private Button btn_send = null;
  // private Button btn_login = null;
  private static final String HOST = "10.0.2.2";
  private static final int PORT = 9999;
  private Socket socket = null;
  private BufferedReader in = null;
  private PrintWriter out = null;
  private String content = "";
  //接收线程发送过来信息，并用TextView显示
  public Handler mHandler = new Handler() {
    public void handleMessage(Message msg) {
      super.handleMessage(msg);
      tv_msg.setText(content);
    }
  };
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    tv_msg = (TextView) findViewById(R.id.TextView);
    ed_msg = (EditText) findViewById(R.id.EditText01);
    btn_send = (Button) findViewById(R.id.Button02);
    try {
      socket = new Socket(HOST, PORT);
      in = new BufferedReader(new InputStreamReader(socket
          .getInputStream()));
      out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(
          socket.getOutputStream())), true);
    } catch (IOException ex) {
      ex.printStackTrace();
      ShowDialog("login exception" + ex.getMessage());
    }
    btn_send.setOnClickListener(new Button.OnClickListener() {
      @Override
      public void onClick(View v) {
        // TODO Auto-generated method stub
        String msg = ed_msg.getText().toString();
        if (socket.isConnected()) {
          if (!socket.isOutputShutdown()) {
            out.println(msg);
          }
        }
      }
    });
    //启动线程，接收服务器发送过来的数据
    new Thread(SocketDemo.this).start();
  }
  /**
   * 如果连接出现异常，弹出AlertDialog！
   */
  public void ShowDialog(String msg) {
    new AlertDialog.Builder(this).setTitle("notification").setMessage(msg)
        .setPositiveButton("ok", new DialogInterface.OnClickListener() {
          @Override
          public void onClick(DialogInterface dialog, int which) {
          }
        }).show();
  }
  /**
   * 读取服务器发来的信息，并通过Handler发给UI线程
   */
  public void run() {
    try {
      while (true) {
        if (!socket.isClosed()) {
          if (socket.isConnected()) {
            if (!socket.isInputShutdown()) {
              if ((content = in.readLine()) != null) {
                content += "\n";
                mHandler.sendMessage(mHandler.obtainMessage());
              } else {
              }
            }
          }
        }
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}