网络编程应用：基于UDP协议【实现文件下载】--练习

要求：

基于UDP协议实现文件下载

发送方–请求–接收方发送文件–发送方接收文件

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代码：

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发送方：

package Homework1;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;

public class Send {
    public static void main(String[] args){
        System.out.println("发送者启动");


        DatagramSocket socket=null;
        FileOutputStream fos=null;
        try {
            //1.发送请求
            socket=new DatagramSocket();
            String string="请求下载文件...";
            DatagramPacket packet=new DatagramPacket(string.getBytes(), string.getBytes().length, InetAddress.getLocalHost(), 6635);
            socket.send(packet);

            //2.创建file对象，以及文件输出流
            File file=new File("b.txt");
            fos=new FileOutputStream(file);

            //3.接收文件
            byte[] buf=new byte[1024];
            while(true){
                DatagramPacket p=new DatagramPacket(buf, buf.length);
                socket.receive(p);
                String string2=new String(p.getData(), 0, p.getLength());

                //4.根据接收方发来的数据，判断文件是否传输完毕
                if(string2.equals("发送完毕")){
                    break;
                }
                fos.write(string2.getBytes());
                fos.flush();
            }

        } catch (SocketException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (UnknownHostException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            if(socket!=null){
                socket.close();
            }
            if(fos!=null){
                try {
                    fos.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }

    }
}

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接收方：

package Homework1;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class Receive {
    public static void main(String[] args){
        System.out.println("接收者启动");


        DatagramSocket socket=null;
        FileInputStream fis=null;
        try {
            //1.创建Datagramsocket对象，相当于TCP中的Socket
            socket=new DatagramSocket(6635);

            //2.创建Datagrampacket对象，用于装数据
            byte[] buf=new byte[1024];
            DatagramPacket packet=new DatagramPacket(buf, buf.length);
            //3.接收数据，收到发送方请求“下载文件”
            socket.receive(packet);
            System.out.println(new String(packet.getData(),0,packet.getLength()));

            //4.发送文件给--发送方
            File file=new File("a.txt");//要给发送方的文件
            fis=new FileInputStream(file);
            byte[] b=new byte[10];
            int count=0;
            while((count=fis.read(b))!=-1){
                DatagramPacket p=new DatagramPacket(b, count,packet.getAddress(),packet.getPort());
                socket.send(p);
            }

            //5.文件发送完后，给--发送方回复一句话
            String string="发送完毕";
            packet=new DatagramPacket(string.getBytes(), string.getBytes().length,packet.getAddress(),packet.getPort());
            socket.send(packet);
        } catch (SocketException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            if(socket!=null){
                socket.close();
            }
            if(fis!=null){
                try {
                    fis.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }   
    }
}

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运行结果：
发送方：

接收方：