学习了基于java 的网络编程，关于udp 的网络编程，这方面的东西前几天难住了哥，现在解决了，做个笔记。同时分享一下给以后的同学。

 UDP是并不是可靠的传输方式,字节序列并没有得到校验,所以传输文件时出现错误也是难免的.因为,txt,doc和jpg本身即使出错也不会影响打开,顶多出现个别字符或是个别像素错误不会影响整体,而exe则是cpu的指令执行序列你错一个就将会导致程序无法执行。

对于文件传输还是建议使用tcp，点对点的传输。

下面是我的代码，希望对各位用。

客服端：

import java.io.FileInputStream;import java.net.DatagramPacket;import java.net.DatagramSocket;import java.net.InetAddress;/** * udp 文件传输,客户端  * @author jun * @date: 2012-11-15 */public class Client {	public static void main(String[] args) {				FileInputStream fis = null;					//file		DatagramSocket sendSocket= null;		//socket		DatagramPacket sendPacket =null;		//send packet		DatagramPacket getPacket = null;		//get packet		InetAddress ip = null;							//ip				try {			sendSocket = new DatagramSocket();			int port = 8888;			ip = InetAddress.getLocalHost();			fis = new FileInputStream("E:\\test.mp3");			byte[] buf =new byte[1024];			int i;						while((i = fis.read(buf, 0, 1024) )==1024){				System.out.println(i);				sendPacket = new DatagramPacket(buf, buf.length, ip,  port);				sendSocket.send(sendPacket);				Thread.sleep(1);	//简单的防止丢包现象			}			System.out.println(i);			sendPacket = new DatagramPacket(buf, 0,i, ip,  port);			sendSocket.send(sendPacket);			Thread.sleep(1);		//简单的防止丢包现象						System.out.println("client send done.");						byte[] getBuf = new byte[1024];			getPacket = new DatagramPacket(getBuf, getBuf.length);			sendSocket.receive(getPacket);			//get feedback message			String backMes = new String(getBuf, 0, getPacket.getLength());			System.out.println("feefBack:"+backMes);		} catch (Exception e) {			e.printStackTrace();		}finally{			try {				if(fis !=null){					fis.close();				}				if(sendSocket != null){					sendSocket.close();				}			} catch (Exception e2) {				e2.printStackTrace();			}		}	}}

import java.io.FileOutputStream;import java.net.DatagramPacket;import java.net.DatagramSocket;import java.net.InetAddress;import java.net.SocketAddress;/** * udp 文件传输，服务端 * @author jun * @date: 2012-11-15 */public class Server {	public static void main(String[] args) {		DatagramSocket serverSocket = null;					//socket 		InetAddress ip = null;											//ip		DatagramPacket getPacket = null; 						//get packet		DatagramPacket sendPacket = null;						//send packet		FileOutputStream fos = null;								//file		int port  = 8888;												//port		//InetAddress sendIP= null;								//send ip		//int sendPort = -1;											//send port		try {			ip = InetAddress.getLocalHost();			serverSocket = new DatagramSocket(port ,  ip);			fos = new FileOutputStream("D:\\test.mp3");			byte[] buf = new byte[1024];			int i=0;			while(true){				getPacket = new DatagramPacket(buf,0,buf.length); 				serverSocket.receive(getPacket);				i = getPacket.getLength();				fos.write(buf,0,i);				if(i<1024){					break;				}			}						//System.out.println("server saved!");			//sendIP = getPacket.getAddress(); 			//sendPort = getPacket.getPort();			SocketAddress sendAddress = getPacket.getSocketAddress(); 			String feedback = "received successfully！";			byte[] backBuf = feedback.getBytes(); 			sendPacket = new DatagramPacket(backBuf,  backBuf.length, sendAddress);			serverSocket.send(sendPacket);			//System.out.println(feedback);		} catch (Exception e) {			e.printStackTrace();		}finally{			try {				serverSocket.close();				fos.close();			} catch (Exception e2) {				e2.printStackTrace();			}		}	}}