在Java项目中使用Socket 如何实现 一个TCP服务端

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * TCP服务器端,单例模式
 * @author xiang
 *
 */
public class TCPServer implements Runnable {
  private static final Logger logger = LoggerFactory.getLogger(TCPServer.class);
  //成员变量/
  private static TCPServer serverInstance;      
  private static Map<String, SocketThread> socketMaps = new HashMap<String,SocketThread>();　　　　　　　　//每个客户端连接时都会新建一个SocketThread与之对应  private static ServerSocket serverSocket;          //服务器套接字
  private static int serPort = 9999;              //服务器端口号
  private static boolean flag;                //服务器状态标志
  private static final int BUFFER_SIZE = 512;          //数据接收字符数组大小
  
  //构造函数/
  private TCPServer() {
    
  }
  
  /**
   * 获取实例
   * @return TCPServer实例serverInstance
   */
  public static TCPServer getServerInstance(){
    if(serverInstance==null)
      serverInstance = new TCPServer();
    return serverInstance;
  }
  
  /**
   * 开启服务器
   * @throws IOException
   */
  public void openTCPServer() throws IOException{    if(serverSocket==null || serverSocket.isClosed()){
      serverSocket = new ServerSocket(serPort);
      flag = true;
    }
  }
  
  /**
   * 关闭服务器
   * @throws IOException 
   */
  public void closeTCPServer() throws IOException{
    flag = false;   if(serverSocket!=null)
      serverSocket.close();
    /*for (Map.Entry<String, SocketThread> entry : socketMaps.entrySet()) { 
       System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());     
    } */ 
    for (SocketThread value : socketMaps.values()) 
      value.closeConnect();
    socketMaps.clear();    
  }
  
  /**
   * 服务器向客户端发送数据
   * @param bytes[]:待发送的字符数组
   * @param key 客户端的key,为空或""时表示数据群发
   * @throws IOException 
   */
  public void sendMessage(String key,byte[] msgBytes){
    if(key==null||key.equals("")){
      for (SocketThread value : socketMaps.values()) 
        value.sendMassage(msgBytes);
    }else{
      SocketThread thread = socketMaps.get(key);
      if(thread!=null)
        thread.sendMassage(msgBytes);
    }
  }
  
  /**
   * 服务器向客户端发送数据
   * @param key 客户端的key,为空或""时表示数据群发
   * @param msgStr:待发送的字符串
   * @throws IOException 
   */
  public void sendMessage(String key,String msgStr){   byte[] sendByte = msgStr.getBytes();
    if(key==null||key.equals("")){
      for (SocketThread value : socketMaps.values()) 
        value.sendMassage(sendByte);
    }else{
      SocketThread thread = socketMaps.get(key);
      if(thread!=null)
        thread.sendMassage(sendByte);
    }
  }
  
  @Override
  public void run() {
    logger.info("服务器线程已经启动");   while(true){
      try {
        while(flag){
          logger.info("服务器线程在监听状态中");
          Socket socket = serverSocket.accept();
          String key = socket.getRemoteSocketAddress().toString();
          SocketThread thread = new SocketThread(socket,key);
          thread.start();
          socketMaps.put(key, thread);          
          logger.info("有客户端连接："+key);
        }        
      } catch (Exception e) {
        e.printStackTrace();        
      } 
    }
  }     
  
  /**
   * 处理连接后的数据接收请求内部类
   * @author xiang
   *
   */
  private class SocketThread extends Thread{
    private Socket socket;
    private String key;
    private OutputStream out;
    private InputStream in;
    
    //构造函数
    public SocketThread(Socket socket,String key) {
      this.socket = socket;
      this.key = key;
    }
    
    /**
     * 发送数据
     * @param bytes
     * @throws IOException 
     */
    public void sendMassage(byte[] bytes){
      try {
        if(out==null)
          out = socket.getOutputStream();
        out.write(bytes);
      } catch (Exception e) {
        e.printStackTrace();
        try {
          closeConnect();
        } catch (IOException e1) {
          e1.printStackTrace();
        }
        socketMaps.remove(key);        
      } 
    }

    /**
     * 关闭连接，释放资源
     * @throws IOException 
     */
    public void closeConnect() throws IOException{
      if(out!=null)  out.close();
      if(in!=null)  in.close();
      if(socket!=null && socket.isConnected())  socket.close();
    }
    
    @Override
    public void run() {
      byte[] receivBuf = new byte[BUFFER_SIZE];
      int recvMsgSize;
      try {
        in = socket.getInputStream();
        out = socket.getOutputStream();
        while ((recvMsgSize = in.read(receivBuf)) != -1) {
          String receivedData = new String(receivBuf, 0, recvMsgSize);
          System.out.println("Reverve form[port" + socket.getPort() + "]:" + receivedData);
          System.out.println("Now the size of socketMaps is" + socketMaps.size());
          /**************************************************************
           * 
           * 接收数据后的处理过程
           * 
           **************************************************************/
        }
        // response to client
        byte[] sendByte = "The Server has received".getBytes();
        // out.write(sendByte, 0, sendByte.length);
        out.write(sendByte);
        System.out.println("To Cliect[port:" + socket.getPort() + "] 回复客户端的消息发送成功");
        closeConnect();
        socketMaps.remove(key);        
      } catch (Exception e) {
        e.printStackTrace();
        try {
          closeConnect();
        } catch (IOException e1) {
          e1.printStackTrace();
        }
      }
    }
    
    //////////////
    public int getport(){
      return socket.getPort();
    }
  }
  //. end SocketThread  
}