1.仿照例15.4，编写基于Socket的多客户/服务器通信程序。

//客户端
import java.io.*;
import java.net.*;
 
public class client3 {
    public static void main(String[] args) {
        try{
            Socket socket=new Socket("127.0.0.1",4700);
            BufferedReader sin=new BufferedReader(new InputStreamReader(System.in));
            PrintWriter os= new PrintWriter(socket.getOutputStream());
            BufferedReader is=new BufferedReader((new InputStreamReader(socket.getInputStream())));
 
            String readline;
            readline=sin.readLine();
            while(!readline.equals("bye")){
                os.println(readline);
                os.flush();
                System.out.println("Client:"+readline);
                System.out.println("server:"+is.readLine());
                readline=sin.readLine();
 
            }
            os.close();
            is.close();
            socket.close();
        }catch(Exception e){
            System.out.println("Error:"+e);
        }
 
    }
}

//服务端
package socket;
import java.io.*;
import java.net.*;
 
class ServerThread extends Thread {
    Socket socket=null; //保存与本线程相关的Socket对象
    int clientnum; //保存本线程的客户计数
 
    public ServerThread(Socket socket,int num) { //构造函数
        this.socket=socket; //初始化socket变量
        clientnum=num+1; //初始化clientnum变量
    }
 
 
    public void run() { //线程主体
        try{
            String line;
            BufferedReader is=new BufferedReader(new
                    InputStreamReader(socket.getInputStream()));
            PrintWriter os=new PrintWriter(socket.getOutputStream());
            BufferedReader sin=new BufferedReader(new InputStreamReader(System.in));
            System.out.println("Client:"+ clientnum +is.readLine());
            line=sin.readLine();
            while(!line.equals("bye")){//如果该字符串为 "bye"，则停止循环
                os.println(line);//向客户端输出该字符串
                os.flush();//刷新输出流，使Client马上收到该字符串
                System.out.println("Server:"+line);
                System.out.println("Client:"+ clientnum +is.readLine());
                line=sin.readLine();//从系统标准输入读入一字符串
            }//继续循环
            os.close(); //关闭Socket输出流
            is.close(); //关闭Socket输入流
            socket.close(); //关闭Socket
        }catch(Exception e){
            System.out.println("Error:"+e);//出错，打印出错信息
        }
    }
 
}
 
 
public class Multitalkserver {
    static int clientnum=0; //静态成员变量，记录当前客户的个数
    public static void main(String args[]) throws IOException {
        ServerSocket serverSocket=null;
        boolean listening=true;
        try{
            //创建一个ServerSocket在端口4700监听客户请求
            serverSocket=new ServerSocket(4700);
        }catch(IOException e) {
            System.out.println("Could not listen on port:4700.");
            System.exit(-1); //退出
        }
        while(listening){ //循环监听
            //监听到客户请求，根据得到的Socket对象和客户计数创建服务线程，并启动之
            new socket.ServerThread(serverSocket.accept(),clientnum).start();
            clientnum++; //增加客户计数
        }
        serverSocket.close(); //关闭ServerSocket
    }
}

2.仿照例15.5，编写基于数据报的多客户/服务器通信程序。

//客户端
import java.io.*;
import java.net.*;
public class QuoteClient {
public static void main(String[] args) throws IOException{
   if(args.length!=1){
    //如果启动的时候没有给出Server的名字，那么打印出错信息并退出
     System.out.println("Usage:java QuoteClient <hostname>");
     return;
   }
  DatagramSocket socket=new DatagramSocket();//创建数据报套接字
    byte[] buf=new byte[256]; //创建缓冲区
    buf = "hello".getBytes();
    InetAddress address=InetAddress.getByName(args[0]);
    //创建DatagramPacket对象
    DatagramPacket packet=new DatagramPacket(buf, buf.length, address, 4445);
    socket.send(packet); //发送
   //创建新的DatagramPacket对象，用来接收数据报
    packet=new DatagramPacket(buf,buf.length);
    socket.receive(packet); //接收
    //根据接收到的字节数组生成相应的字符串
    String received=new String(packet.getData());
    //打印生成的字符串
    System.out.println("Quote of the Moment:"+received ); 
    //关闭套接口
    socket.close();
   }
}

//服务端
public class QuoteServer{
 public static void main(String args[]) throws IOException {
   new QuoteServerThread().start();//启动一个QuoteServerThread线程
 }
}
import java.io.*;
import java.net.*;
public class QuoteServerThread extends Thread { 
   protected DatagramSocket socket=null;//本线程关联的DatagramSocket对象
   protected BufferedReader in=null;  //用来读文件的一个Reader
   protected boolean moreQuotes=true; //标志变量，是否继续操作
   public QuoteServerThread() throws IOException { //无参数的构造方法
     this("QuoteServerThread");
   }
   public QuoteServerThread(String name) throws IOException {
     super(name); //调用父类的构造方法
     socket=new DatagramSocket(4445);//在端口4445创建数据报套接字
     in= new BufferedReader(new InputStreamReader(System.in));}
public void run() {//线程主体
   while(moreQuotes) {
   try{
      byte[] buf=new byte[256]; //创建缓冲区
      DatagramPacket packet=new DatagramPacket(buf,buf.length);
      socket.receive(packet); //接收数据报
      System.out.println(new String(packet.getData())); 
      String dString= in.readLine(); //终端输入字符串   
      //如果是bye,则向客户端发完消息后退出
      if(dString.equals("bye")){ moreQuotes=false;}
      buf=dString.getBytes();//把String转换成字节数组，以便传送
      InetAddress address = packet.getAddress(); //Client地址
      int port=packet.getPort(); // Client端口号
       //构建发送DatagramPacket对象
       packet=new DatagramPacket(buf,buf.length,address,port);
       socket.send(packet); //发送数据报
   }catch(IOException e) { //异常处理
       e.printStackTrace(); //打印错误栈
       moreQuotes=false; //标志变量置false，以结束循环
    }
}
 socket.close(); //关闭数据报套接字
}
}