第五章：网络编程（下）

1.Socket多客户端通信实现

1.客户端程序代码：

客户端代码与第四章中客户端代码相同，不再累述。

2.服务器端程序代码：

//MultiTalkeServer.java文件
import java.io.*;
import java.net.*;
 
public class MultiTalkServer {
       static int clientnum = 0;//统计客户端数量
 
       public static void main(String[] args) throws IOException {
              // TODO Auto-generated method stub
              ServerSocket server = null;//声明一个serversocket对象
              boolean listening = true;
              try {
                            server = 
                            new ServerSocket(4700);
                     }catch(IOException e) {
                    System.out.println("could not listen on port:4700" );
                     }
                     Socket socket = null;
                     try {
                            socket = server.accept();
                     }catch(Exception e) {
                            System.out.println("Error."+e);
                            System.exit(-1);
                     }
                     while(listening)
                     {
                            new ServerThread(serverSocket.accept(),
clientnum).start();
                            clientnum++;
                     }
                     serverSocket.close();
       }
}
//ServerThread.java文件代码
import java.io.*;
import java.net.*;
 
public class ServerThread extends Thread {
       Socket socket = null;
       int clientnum;
       public ServerThread(Socket socket, int num){
              this.socket = socket;
              clientnum = num+1;
       }
       public void run(){
              try{
                     //下面开始通信。
                     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"))
                     {
                            os.println(line);
                            os.flush();
                                                
                            //下面是打印客户端和服务器端发送的信息
                            System.out.println("Server:"+ line);
                            System.out.println("Client:"+ clientnum
+":" + is.readLine());
                            line = sin.readLine();
                     }
                     os.close();
                     is.close();
                     socket.close();
              }catch(Exception e) {\
                     System.out.println("Error:"+e);
              }
       }
 
}

2.数据报通信

数据包通信采用的是UDP(User Datagram Protocol)，它是非面向连接的，提供不可靠的数据包式的数据传说的协议，类似于从邮局发送信件的过程。Java中的DatagramPacket/DatagramSocket/MulticastSocket等累使用UDP协议进行网络通信。

TCP(Transport Control Protocol)是面向对接的能够提供可靠的流式数据传输的协议。Java中的ULR/URLConnection/socket/serverSocket等类使用TCP协议进行网络通信。

1.TCP和UDP的区别

（1）TCP有建立时间，UDP没有；

（2）UDP传输限制包在64k以内；

（3）TCP的应用有Telnet、FTP等，UDP的应用有ping等。

2.Java中进行数据报通信

所用的类有：

①DatagramSocket()//只允许数据报发往一个目的地址

②DatagramSocket(int port)

③DatagramPacket(byte ibuf[], int ilength)//接受

④DatagramPacket(byte ibuf[], int ilength， InetAdress iaddr, int iport)；//发送

收数据报：

DatagramPacket packet = new DatagramPacket(buf, 256);
socket.receive(packet);

发数据报：

DatagramPacket packet = new DatagramPacket(buf, buf.length,address,port);
socket.send(packet);

例：客户方程序QuoteClient.java

代码：

import java.io.*;
import java.net.*;
import java.util.*;
public class QuoteClient {
       public static void main(String[] args) throws IOException{
              if(args.length!=1){//如果没有参数的执行内容
                     System.out.println("Usage:java QuoteClient<hostname");
                     return
              }
              DatagramPacket packet = new DatagramPacket();
              //send request
              byte[] buf = new byte[256];
              InetAddress address = InetAddress.getByName(args[0]);
              DatagramPacket packet = new
 DatagramPacket(buf, buf.length,address,4445);
              socket.send(packet);
              //get response
               packet = new DatagramPacket(buf, buf.length);
               socket.receive(packet);
               //display response
               String received = new String(packet.getData());
               System.out.println("Quote of the Moment:" +received);
               socket.close();
       }
}

例：服务器方程序QuoteServer.java

代码：

public class QuoteServer{
       public static void main(String[] args) throws java.io.IOException{
              new QuoteServerThread().start();
       }
}

例：服务器方程序QuoteServerThread.java

代码：

import java.io.*;
import java.net.*;
import java.util.*;
public class QuoteServerThread extends Thread {
       protected DatagramSocket socket = null;
       protected BufferedReader in =null;
       protected boolean moreQuotes = true;
       public QuoteServerThread() throws IOException{
              this("QuoteServerThread");
       }
       public QuoteServerThread(String name) throws IOException{
              super(name);
              socket  = new DatagramSocket(4445);
              try{
                     in = new BufferedReader(new FileReader("one-liners.txt"));
              }catch(FileNotFoundException e){
                     System.err.println
("Counldnot open quote file.Serving time instead.");
              }
       }
       public void run(){
              while(moreQuotes){
                     try{
                            byte[] buf =new byte[256];
                            DatagramPacket packet =
new DatagramPacket(buf,buf.length);
                            socket.receive(packet);
                            String dString = null;
                            if(in==null)
                                   dString = new Date().toString();
                            else dString = getNextQuote();
                            buf =dString.getBytes();
                            //send the response to the client at "address"
                            //and "port"
                            InetAddress address = packet.getAddress();
                            int port = packet.getPort();
                            packet =
new DatagramPacket(buf,buf.length,address,port);
                            socket.send(packet);
                     }catch(IOException e){
                            e.printStackTrace();
                            moreQuotes=false;
                     }
              }
              socket.close();
       }
       protected String getNextQuote(){
              String returnValue = null;
              try{
                     if((returnValue=in.readLine())==null){
                            in.close();
                            moreQuotes=false;
                            returnValue = "No more quotes.Goodbye.";
                     }catch(IOException e){
                            returnValue="IOException occurred in server";
                     }
                     return returnValue;
              }
       }
}

3.使用数据报进行广播通信

MulticastSocket讲数据报以广播方式发送到该端口的所有客户。

例：客户方程序MulticastClient.java

代码：

import java.io.*;
import java.net.*;
import java.util.*;
public class MulticastClient {
       public static void main(String[] args) throws IOException{
              MulticastSocket socket = new MulticastSocket(4446);
              InetAddress address = InetAddress.getName("230.0.0.1");
              socket.joinGroup(address);
              DatagramPacket packet;
              //get a few quotes
              for(int i = 0;i<5;i++){
                     byte[] buf = new byte[256];
                     packet = new DatagramPacket(buf,buf.length);
                     socket.receive(packet);
                     String received = new String(packet.getData());
                     System.out.println
("Quote of the Moment:" +received);
              }
              socket.leaveGroup(address);
              socket.close();
       }
}

例：客户方程序MulticastServer.java

代码：

public class MulticastServer{
       public static void main(String args[])
 throws java.io.IOException{
              new MulticastServerThread().start();
       }
}

例：服务器方程序QuoteServerThread.java

代码：

import java.io.*;
import java.net.*;
import java.util.*;
public class MulticasterverThread extends Thread {
       private long FIVE_SECOND=5000;
       public MulticastServerThread() throws IOException{
              super("MulticastServerThread");
       }
       public void run(){
              while(moreQuotes){
                     try{
                            byte[] buf = new byte[256];
                            //construct quote
                            String dString = null;
                            if(in==null)
                                   dString = new Date().toString();
                            else dString = getNextQuote();
                            buf =dString.getBytes();
                            //send it
                            InetAddress group =
InetAddress.getByName("230.0.0.1");
                            DatagramPacket pacet = new
DatagramPacket(buf,buf.length,group,4446);
                            socket.send(packet);
                            //sleep for a while
                            try{
                                   sleep((long)(Math.random()*FIVE_SECOND));
                            }catch(InterruptedException e){}
                     }catch(IOException e){
                            e.printStackTrace();
                            moreQuotes=false;
                     }
              }
              socket.close();
       }
}