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();
}
}