多客户端和服务器通信的基本流程：

package com.bwf.tcp_cleint;

import java.text.SimpleDateFormat;
import java.util.Date;

import android.os.Build;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ScrollView;
import android.widget.TextView;
/**
 * 多客户端和服务器通信的基本流程：
 *         1. 在某个客户端的EditText输入要发送的内容
 *         2. 点击Button的时候把要发送的内容通过Handler发送到子线程CleintHandler
 *         3. 子线程中的CleintHandler收到MSG之后，把其中的数据通过Socket流写入
 *         4. 在Server端会读取到客户端写入的内容
 *         5. 在Server中把读取到的数据分别写入所有Socket
 *         6. 可以在客户端的子线程中读取到Server发送的信息
 *         7. 在子线程中通过UIHandler发消息，通知UI来更新
 *         8. 重复上述过程
 * */
public class MainActivity extends Activity {
    SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    EditText edt_input;
    TextView tv_show;
    Button btn_send;
    
    CleintThread cleintThread;
    
    // 更新UI上TextView显示
    Handler uiHandler;
    
    // ScrollView
    ScrollView scrollView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        init();
    }

    Build bd = new Build();    
    String model;
    private void init() {
        model = bd.MODEL;
        edt_input = (EditText) findViewById(R.id.edt_input);
        tv_show = (TextView) findViewById(R.id.tv_show);
        scrollView = (ScrollView) findViewById(R.id.scrollView);
        
        uiHandler = new Handler(){
                public void handleMessage(android.os.Message msg) {
                    if(msg.what == 0){
                        tv_show.append(msg.obj+"
");
                        // 滑动到底部
                        scrollView.fullScroll(ScrollView.FOCUS_DOWN);
                        // 滑动到顶部
                        //scrollView.fullScroll(ScrollView.FOCUS_UP);
                    }
                };
            };
        
        cleintThread = new CleintThread(uiHandler);
        // 启动客户端线程
        new Thread(cleintThread).start();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    public void mainClick(View v){

package com.bwf.tcp_cleint;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.UnsupportedEncodingException;
import java.net.Socket;
import java.net.UnknownHostException;
import java.text.SimpleDateFormat;
import java.util.Date;

import android.os.Build;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.util.Log;

public class CleintThread implements Runnable {
    SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

    Handler handler;

    public Handler cleintHandler;

    Socket s;
    BufferedReader br;
    OutputStream out;

    public CleintThread(Handler handler) {
        super();
        this.handler = handler;
    }

    @Override
    public void run() {
        try {
            s = new Socket("192.168.10.124", 8000);
            br = new BufferedReader(new InputStreamReader(s.getInputStream()));

            out = s.getOutputStream();

            // 开启一个线程读取服务器返回的数据
            new Thread(new Runnable() {

                @Override
                public void run() {

                    String data = "";
                    try {
                        while ((data = br.readLine()) != null) {
                            // 读取到服务器返回时，发消息给UI中的Handler更新UI
                            Message msg = Message.obtain();
                            msg.what = 0;
                            msg.obj = data;
                            handler.sendMessage(msg);
                        }
                    } catch (Exception e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            }).start();

            // 准备Looper
            Looper.prepare();
            // 创建Handler以便接收处理UI端发送来的消息，将其写入Socket流中
            cleintHandler = new Handler() {
                @Override
                public void handleMessage(Message msg) {
                    if (msg.what == 1) {
                        try {
                            String name = new Build().MODEL;
                            int len = name.length();
                            int nameMax = 20;
                            if(len < nameMax){
                                for (int i = 0; i < nameMax - len; i++) {
                                    name += " ";
                                }
                            } else{
                                name = name.substring(0, nameMax);
                            }
                            
                            out.write((name
                                    + format.format(new Date(System
                                            .currentTimeMillis()))
                                    + "
" + msg.obj+"
")
                                    .getBytes("utf-8"));
                        } catch (Exception e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                    }
                }
            };

            // 激活消息队列
            Looper.loop();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            Log.d("fanhy", "连接服务器失败。");
            e.printStackTrace();
        }
    }

}

        switch (v.getId()) {
        case R.id.btn_send:
            Message msg = Message.obtain();
            msg.what = 1;
            msg.obj = edt_input.getText()+"";
            // 将EditText中的输入传递给客户端线程进行发送到服务器
            cleintThread.cleintHandler.sendMessage(msg);
            // 发送后清空EditText
            edt_input.setText("");
            break;

        default:
            break;
        }
    }
}