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 = newDatagramPacket(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(); }} 