udpserver.java

这是用java编写的用UDP协议的模拟FTP客户端和服务器的程序。

import java.net.*;
import java.io.*;

public class UdpServer
{
	public static void main (String args[])
	{
		DatagramSocket dSocket=null;
		int port=2000;
		int length=1024;
		
		try
		{
			// 建立Socket
			dSocket = new DatagramSocket(port);
			System.out.println ("UDP service started");

			for(;;)
			{
				// 建立空Package
				DatagramPacket p = new DatagramPacket( new byte[length], length );
				
				// 接收文件名
				dSocket.receive(p);
				
				// 获取文件名
				String fileName = new String (p.getData(), 0, p.getLength());
				InetAddress addr = p.getAddress();
				System.out.println ("Received request from " +
							addr.getHostAddress() + ":" +
							p.getPort() +
							"\nFileName : " + fileName);
	
				// 读文件，并发送
				FileInputStream fin = new FileInputStream(fileName);
				int data = 0;
				for (;;)				
				{
					// 生成输出包
					byte[] barray = new byte[length];
					
					int i;
					for (i=0; i<length; i++)
					{
						data = fin.read();
						barray[i] = (byte)data;
						if (data==-1) break;
					}
					p.setData(barray);
					p.setLength(i);
					
					// 发送包
					dSocket.send (p);

					// 接收确认包
					dSocket.receive(p);
					
					// 发送结束标志
					if (data==-1)
					{
						String s = fileName + "End.";
						barray = s.getBytes ();
						p.setData(barray);
						p.setLength(barray.length);
						dSocket.send (p);
						break;
					}
				}
				
				fin.close();
				System.out.println ("Packet sent to " +
							addr.getHostAddress() + ":" +
							p.getPort());
			}
		}
		catch (IOException ioe)
		{
			System.err.println ("Error - " + ioe);
		}
		dSocket.close();
	}
}