gbnclient.java

网络实验：用JAVA语言实现电子邮件的发送功能！有图形界面。

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

public class GBNClient
{
	public void go() throws IOException,UnknownHostException
	{
		DatagramSocket datagramSocket;
		DatagramPacket inDataPacket;
		DatagramPacket outDataPacket;
		InetAddress serverAddress;
		byte[] msg = new byte[1];
		int i = 0,j;
		String[] data = {"first","second","third","forth","end"};
		String da;
		String en = "complete";
		int prev = -1;
		int rec = 0;
		String receivedMsg;
		datagramSocket = new DatagramSocket();
		serverAddress = InetAddress.getLocalHost();
		while(!data[i].equals("end"))
		{
			da = i + data[i];
			outDataPacket = new DatagramPacket(da.getBytes(),da.getBytes().length,serverAddress,8000);
			datagramSocket.send(outDataPacket);
			i++;
		}
		da = i + data[i];
		outDataPacket = new DatagramPacket(da.getBytes(),da.getBytes().length,serverAddress,8000);
		datagramSocket.send(outDataPacket);
		while(true){
		inDataPacket = new DatagramPacket(msg,msg.length);
		datagramSocket.receive(inDataPacket);
		receivedMsg = new String(inDataPacket.getData(),0,inDataPacket.getLength());
		prev = rec;
		rec = Integer.parseInt(receivedMsg);
		System.out.println(rec + 1);
		if(rec == (prev + 1) && (rec == 4))
				break;
		else if(rec == (prev + 1))
				continue;
		else if(rec > prev + 1)
		{
			j = prev + 1;
			System.out.println("Ack " + (j+1) + " lost. Resend....");
			while(!data[j].equals("end"))
			{
				da = j + data[j];
				outDataPacket = new DatagramPacket(da.getBytes(),da.getBytes().length,serverAddress,8000);
				datagramSocket.send(outDataPacket);
				j++;
			}
			da = j + data[j];
			outDataPacket = new DatagramPacket(da.getBytes(),da.getBytes().length,serverAddress,8000);
			datagramSocket.send(outDataPacket);
		}
		}
		outDataPacket = new DatagramPacket(en.getBytes(),en.getBytes().length,serverAddress,8000);
		datagramSocket.send(outDataPacket);
		System.out.println("Data send complete!");
	}
	public static void main(String[] args)
	{
		GBNClient gbn = new GBNClient();
		try
		{
			gbn.go();
		}
		catch(Exception e)
		{
			System.out.println("Exception occured with socket");
		}
	}
}