java网络编程——基于UDP和TCP协议的小例子

网络编程3要素：

1.IP地址：目的主机的唯一标识

2.port端口号：目的主机上的目标程序的唯一标识

3.protocol：协议；分为udp和tcp

通信原理：

1.无论是udp还是tcp其通信底层都是由socket（套接字：包括IP和port端口两部分）来实现的；

2.数据：

udp将数据封装在数据报包（DatagramPacket）对象内；

TCP通信的两端直接是输入输出流；

原理图：

下面通过代码来加深理解：

一、基于UDP的简单通信程序

接收端：

import java.io.IOException;import java.net.DatagramPacket;import java.net.DatagramSocket;public class ReceiveDemo {public static void main(String[] args) throws IOException {// 创建socketDatagramSocket socket = new DatagramSocket(9999);// 创建接受包byte[] buf = new byte[1024];DatagramPacket packet = new DatagramPacket(buf, buf.length);// 接受数据socket.receive(packet);// 阻塞式// 解析数据String ip = packet.getAddress().getHostAddress();String content = new String(packet.getData(), 0,packet.getLength());System.out.println("From:" + ip + "\n" + "content: " + content);// 释放资源socket.close();}}

发送端：

import java.io.IOException;import java.net.DatagramPacket;import java.net.DatagramSocket;import java.net.InetAddress;import java.net.UnknownHostException;public class SendDemo {public static void main(String[] args) throws IOException,UnknownHostException {// 创建socket对象DatagramSocket socket = new DatagramSocket();// 创建发送包(ip+port在包上，因为是把包发送出去，让包去寻找目的主机上的目标端口)byte[] buf = "hello udp !".getBytes();DatagramPacket packet = new DatagramPacket(buf, buf.length, InetAddress.getByName("192.168.1.100"), 9999);// 发送socket.send(packet);// 释放资源socket.close();}}

二、基于TCP的简单通信程序

接收端：

import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.net.ServerSocket;import java.net.Socket;public class ServerDemo {public static void main(String[] args) throws IOException {// 创建服务器socket对象ServerSocket ss = new ServerSocket(8888);// 监听客户端的连接Socket socket = ss.accept();// 阻塞// 获取输入流InputStream is = socket.getInputStream();byte[] buf = new byte[1024];// This method blocks until input data is available, end of file is// detected, or an exception is thrown.int len = is.read(buf);String content=new String(buf, 0, len);System.out.println("收到内容："+content);//获取输出流，并向客户端反馈（可选）OutputStream os=socket.getOutputStream();os.write("Server Received!".getBytes());//释放资源socket.close();//注意：服务器一般是不关的//ss.close();}}

客户端：

import java.io.InputStream;import java.io.OutputStream;import java.net.Socket;public class ClientDemo {public static void main(String[] args) throws Exception {// 创建客户端socket对象Socket s = new Socket("192.168.1.100", 8888);// 获取输出流，并写入数据OutputStream os = s.getOutputStream();os.write("hello ,tcp".getBytes());// 获取输入流，从中取出服务端的反馈信息InputStream is = s.getInputStream();byte[] buf = new byte[1024];int len = is.read(buf);String content = new String(buf, 0, len);System.out.println("反馈内容：" + content);}}