TCP与UDP网络编程

一、TCP与UDP的区别：

**主要抓住是否服务端与客户端需要建立连接这一关键点。

1）TCP要求服务端与客户端之间要先建立连接才能进行通信，比如打电话。TCP工作与传输层，是可靠的协议。由于要先建立连接，故效率也相对较低，一般用于大数据量的传输。

2）UDP则是服务端与客户端之间不用先建立连接就能进行通信，比如qq、微信。只负责将信息发出，不管信息是否成功传出。因此是不可靠的传输协议。但由于无需事先建立连接，故传输速度较快，效率比较高。但是传输的数据量有限制，并且较为容易出现丢包现象。

二、TCP与UDP编程实例

--------------------用UDP协议实现一个聊天程序---------------------

利用的技术：多线程，接口

package haha;

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.InetAddress;

import java.net.SocketException;

/**

 * 编写一个聊天程序

 * 使用多线程

 * @author Administrator

 *

 */

class Send implements Runnable

{
private DatagramSocket ds;
Send(DatagramSocket ds)
{
this.ds = ds;
}
@Override
public void run() {
// TODO Auto-generated method stub
BufferedReader bufr = new BufferedReader(new InputStreamReader(System.in));
String line = null;
try {
while((line=bufr.readLine())!=null)
{
if("123".equals(line))
{
break;
}
byte[] buf = line.getBytes();
DatagramPacket dp =new DatagramPacket(buf, buf.length,InetAddress.getByName("172.27.33.8"),10003);
ds.send(dp);
}
} catch (IOException e) {
throw new RuntimeException("发送端出错！");
}
}

}

class Rece implements Runnable

{
private DatagramSocket ds;
Rece(DatagramSocket ds)
{
this.ds = ds;
}
@Override
public void run() {
// TODO Auto-generated method stub
while(true)
{
byte [] buf = new byte[1024];
DatagramPacket dp = new DatagramPacket(buf, buf.length);
try {
ds.receive(dp);

String ip =dp.getAddress().getHostAddress();
String data = new String(dp.getData(),0,dp.getLength());
} catch (IOException e) {

throw new RuntimeException("接收端出错！");
}

}
}

}

public class ChatDemo

{
public static void main(String [] args) throws Exception
{
DatagramSocket sendSocket = new DatagramSocket();
DatagramSocket receSocket = new DatagramSocket(10003);
new Thread(new Send(sendSocket)).start();
new Thread(new Rece(receSocket)).start();
}

}

------------------------用TCP协议实现用户登录操作-----------------

需求：//用户进行登录，最多登录三次

客户端代码：

public class UserLoginClientDemo {

/**
* @param args
* @throws Exception 
* @throws UnknownHostException 
*/
public static void main(String[] args) throws UnknownHostException, Exception {
// TODO Auto-generated method stub
Socket s = new Socket("172.27.33.8", 10025);

BufferedReader bufr = new BufferedReader(new InputStreamReader(System.in));

PrintWriter out = new PrintWriter(s.getOutputStream(),true);

BufferedReader bufIn = new BufferedReader(new InputStreamReader(s.getInputStream()));

for(int i=0 ; i<3 ; i++)
{
String line = bufr.readLine();
if(line==null)
break;

out.println(line);

String info = bufIn.readLine();
System.out.println("info:"+info);

if(info.contains("欢迎"))//一次登录成功
break;

}
bufr.close();
s.close();
}

}

服务端代码：

public class UserLoginServerDemo {

/**
* @param args
* @throws Exception 
*/
public static void main(String[] args) throws Exception {
// TODO Auto-generated method stub
ServerSocket ss = new ServerSocket(10025);

while(true)
{
Socket s = ss.accept();

new Thread(new UserThread(s)).start();
}

}

}

class UserThread implements Runnable

{
private Socket s;

public UserThread(Socket s) {
this.s = s;
}

public void run() {
// TODO Auto-generated method stub
String ip = s.getInetAddress().getHostAddress();
System.out.println(ip+"......connected....");
try {
for(int i=0;i<3;i++)
{
BufferedReader bufIn = new BufferedReader(new InputStreamReader(s.getInputStream()));
String name = bufIn.readLine();

if(name==null)
{
break;
}

BufferedReader bufr = new BufferedReader(new FileReader("C:\\user.txt"));
PrintWriter out = new PrintWriter(s.getOutputStream(),true);

String line = null;

boolean falg = false;

while((line=bufr.readLine())!=null)
{
if(line.equals(name))
{
falg  = true;
break;
}
}

if(falg)
{
System.out.println(name+"，已登录");
out.println(name+"，欢迎光临！");
break;
}
else
{
System.out.println(name+"尝试登录");
out.println(name+"用户名不存在！");
}

}
s.close();//关闭客户端
} catch (IOException e) {
throw new RuntimeException(ip+"校验失败！");
}
}

}

三、总结

1）TCP程序执行时必须先启动服务端，客户端向服务端发出请求，只有先开启服务端，程序才不会报错

2）在服务端尽量设置时间限制，节省资源

3）在服务端得用多线程，这样能解决多个客户端登录一个服务端