java基础教程-网络编程(七)

七、网络编程

7.1．IP协议

　　最重要的贡献是IP地址

7.2．TCP和UDP协议

　　TCP（快）可靠传输，发送时必须建立连接（三次握手协议 ）

　　UDP（慢）不可靠传输，发送时无须建立连接

7.3．TCP 的TCP Server和TCP Client

　　注意，要首先启动Server，再启动Client

　　端口号是应用的入口，有两个字节，所以每个服务器最多能运行65536个应用程序，而TCP的端口和UDP的端口不一样，定义端口时，尽量定义1024以上的。

　　特别典型的端口号，http  80；

//TCP Server

import java.net.*;

import java.io.*;

public class TCPServer {

public static void main(String[] args) throws Exception {

ServerSocket ss = new ServerSocket(6666);

while(true) {

Socket s = ss.accept();//阻塞函数，一直在这等，直到有访问，才会继续执行

System.out.println("a client connect!");

DataInputStream dis = new DataInputStream(s.getInputStream());

System.out.println(dis.readUTF());

dis.close();

s.close();

}

}

}

//TCP Client

import java.net.*;

import java.io.*;

public class TCPClient {

public static void main(String[] args) throws Exception {

Socket s = new Socket("127.0.0.1", 6666);

OutputStream os = s.getOutputStream();

DataOutputStream dos = new DataOutputStream(os);

Thread.sleep(3000);

dos.writeUTF("hello server!");

dos.flush();

dos.close();

s.close();

}

}

7.4．UDP   Server和Client（UDP只能传送字节数组）

//UDP   Server

import java.net.*;

public class TestUDPServer

{

public static void main(String args[]) throws Exception

{

byte buf[] = new byte[1024];

DatagramPacket dp = new DatagramPacket(buf, buf.length);

DatagramSocket ds = new DatagramSocket(5678);

while(true)

{

ds.receive(dp);

System.out.println(new String(buf,0,dp.getLength()));//String的构造函数

}

}

}

//UDP Client

import java.net.*;

public class TestUDPClient

{

public static void main(String args[]) throws Exception

{

byte[] buf = (new String("Hello")).getBytes();

DatagramPacket dp = new DatagramPacket(buf, buf.length, 

   new InetSocketAddress("127.0.0.1", 5678)

   );

DatagramSocket ds = new DatagramSocket(9999);//client自己的端口，因为UDP不是面向连接的

ds.send(dp);

ds.close();

}

}

//TestUDP Client

import java.net.*;

import java.io.*;

public class TestUDPClient

{

public static void main(String args[]) throws Exception

{

long n = 10000L;

ByteArrayOutputStream baos = new ByteArrayOutputStream();

DataOutputStream dos = new DataOutputStream(baos);

dos.writeLong(n);

byte[] buf = baos.toByteArray();//将long型数据转化成字符数组的形式，进行输入

System.out.println(buf.length);

DatagramPacket dp = new DatagramPacket(buf, buf.length, 

   new InetSocketAddress("127.0.0.1", 5678)

   );

DatagramSocket ds = new DatagramSocket(9999);

ds.send(dp);

ds.close();

}

}

//TestUDP Server

import java.net.*;

import java.io.*;

public class TestUDPServer

{

public static void main(String args[]) throws Exception

{

byte buf[] = new byte[1024];

DatagramPacket dp = new DatagramPacket(buf, buf.length);

DatagramSocket ds = new DatagramSocket(5678);

while(true)

{

ds.receive(dp);

ByteArrayInputStream bais = new ByteArrayInputStream(buf);

DataInputStream dis = new DataInputStream(bais);

System.out.println(dis.readLong());//将字符数组读成long型

}

}

}