* 网络端口不是物理端口，是逻辑端口；MySQL：3306  网络：80   

 * IP公网现在不是一个人一个IP了，一片区域一个公网IP。  本地回环地址：127.0.0.1对应本地主机名localhost

 * 传输层：udp（即时聊天，网络会议） tcp（下载，打电话）

 * 网络层：ip  （InetAddress）

 * 应用层：HTTP  FTP  

UDP例子程序：

package javaBase.net;import java.net.*;/* * 发送端 */public class UdpSend {	public static void main(String[] args) throws Exception{		//1,创建udp服务，DatagramSocket（）；		DatagramSocket ds = new DatagramSocket(8888);//自定义数字标识8888		//2,确定数据，并封装成数据包		byte[] buf = "udp said  i am coming".getBytes();		DatagramPacket dp = new DatagramPacket(buf, buf.length, InetAddress.getByName("192.168.1.4"),10000);		//3,用send()方法，发送数据包		ds.send(dp);		//4,关闭资源		ds.close();	}}

package javaBase.net;import java.io.*;import java.net.DatagramPacket;import java.net.DatagramSocket;/* * 接收端 */public class UdpReceive {	public static void main(String[] args) throws Exception{		//1,创建udp socket，建立端点		DatagramSocket ds = new DatagramSocket(10000);//指定端口数字标识		//2,定义接收包，存放接收到的数据		byte[] buf = new byte[1024];		DatagramPacket dp = new DatagramPacket(buf, buf.length);		//3,通过receive()方法，接收数据并写入包中		ds.receive(dp);		//4,从包中提取数据		String ip = dp.getAddress().getHostAddress();//获取本机IP？		int port = dp.getPort();//获取发送端端口  		String data = new String(dp.getData(),0,dp.getLength());//获取数据		System.out.println(ip+" : "+port+"["+data+"]");		//5,关闭资源		ds.close();					}}

键盘输入，循环接收：

发送端：

package javaBase.net;import java.io.BufferedReader;import java.io.InputStreamReader;import java.net.*;/* * 发送端 */public class UdpSend {	public static void main(String[] args) throws Exception{		send2();	}	/*	 * 键盘输入	 */	public static void send2() throws Exception{		DatagramSocket ds = new DatagramSocket(8888);		BufferedReader in =				new BufferedReader(new InputStreamReader(System.in));		String line = null;		while((line = in.readLine())!=null){			if("over".equals(line))				break;			byte[] buf = line.getBytes();			DatagramPacket dp = 					new DatagramPacket(buf, buf.length,InetAddress.getByName("localhost"),10000);			ds.send(dp);		}		ds.close();	}	/*	 * 详细步骤，一次性	 */	public static void send1()throws Exception{		//1,创建udp服务，DatagramSocket（）；		DatagramSocket ds = new DatagramSocket(8888);//自定义数字标识8888		//2,确定数据，并封装成数据包		byte[] buf = "udp said  i am coming".getBytes();		DatagramPacket dp = 				new DatagramPacket(buf, buf.length, InetAddress.getByName("192.168.1.4"),10000);		//3,用send()方法，发送数据包		ds.send(dp);		//4,关闭资源		ds.close();	}}

接收端：

package javaBase.net;import java.io.*;import java.net.DatagramPacket;import java.net.DatagramSocket;/* * 接收端 */public class UdpReceive {	public static void main(String[] args) throws Exception{		receive2();			}	/*	 * 循环等待接收	 */	public static void receive2() throws Exception{		DatagramSocket ds = new DatagramSocket(10000);		while(true){			byte[] buf = new byte[1024];			DatagramPacket dp = new DatagramPacket(buf, buf.length);			ds.receive(dp);			String ip = dp.getAddress().getHostAddress();			String data = new String( dp.getData(),0,dp.getLength());			System.out.println(ip+": "+data );		}			}	/*	 * 详细步骤	 */	public static void receive1()	throws Exception{		//1,创建udp socket，建立端点		DatagramSocket ds = new DatagramSocket(10000);//指定端口数字标识		//2,定义接收包，存放接收到的数据		byte[] buf = new byte[1024];		DatagramPacket dp = new DatagramPacket(buf, buf.length);		//3,通过receive()方法，接收数据并写入包中		ds.receive(dp);		//4,从包中提取数据		String ip = dp.getAddress().getHostAddress();//获取发送端IP？		int port = dp.getPort();//获取发送端端口  		String data = new String(dp.getData(),0,dp.getLength());//获取数据		System.out.println(ip+" : "+port+"["+data+"]");		//5,关闭资源		ds.close();	}}

即时聊天程序

package javaBase.net;import java.net.*;import java.io.*;/* * 发送线程 */class Send implements Runnable{	//成员socket	private DatagramSocket ds ;	//构造方法接收传入socket	public Send(DatagramSocket ds) {		this.ds = ds;	}	@Override	public void run() {		try {			BufferedReader in =					new BufferedReader(new InputStreamReader(System.in));			String line = null;			while((line = in.readLine())!=null){				if("over".equals(line))					break;				byte[] buf = line.getBytes();				DatagramPacket dp = 						new DatagramPacket(buf, buf.length,InetAddress.getByName("localhost"),10002);				ds.send(dp);			}		} catch (Exception e) {			throw new RuntimeException("发送端错误");		}			}}/* * 接收线程 */class Receive implements Runnable{	//成员socket	private DatagramSocket ds ;	//构造方法初始化socket	public Receive(DatagramSocket ds) {		this.ds = ds;	}	@Override	public void run() {		try {			while(true){				byte[] buf = new byte[1024];				DatagramPacket dp = new DatagramPacket(buf, buf.length);				ds.receive(dp);				String ip = dp.getAddress().getHostAddress();//先看一下谁发过的呀！				String data = new String(dp.getData(),0,dp.getLength());//看看发的什么东西				System.out.println(ip+": "+data);			}					} catch (Exception e) {			throw new RuntimeException("接收端错误");		}			}}public class Chat {	public static void main(String[] args) throws Exception{		DatagramSocket sendSocket = new DatagramSocket();//发送端可以随机端口号		DatagramSocket receiveSocket = new DatagramSocket(10002);//接收端指定端口		new Thread(new Send(sendSocket)).start();		new Thread(new Receive(receiveSocket)).start();	}}