Java开发之多线程下载和断点续传

代码实现了多线程下载和断点续传功能

 import java.io.BufferedReader;
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.io.RandomAccessFile;
 import java.net.HttpURLConnection;
 import java.net.URL;

 import javax.print.attribute.standard.Finishings;

 public class MultiDownload {

     static int ThreadCount = 3;
     static int finishedThread = 0;
     //确定下载地址
     static String path = "http://192.168.13.13:8080/QQPlayer.exe";
     public static void main(String[] args) {

         //发送get请求，请求这个地址的资源
         try {
             URL url = new URL(path);
             HttpURLConnection conn = (HttpURLConnection) url.openConnection();
             conn.setRequestMethod("GET");
             conn.setConnectTimeout(5000);
             conn.setReadTimeout(5000);

             if(conn.getResponseCode() == 200){
                 //拿到所请求资源文件的长度
                 int length = conn.getContentLength();

                 File file = new File("QQPlayer.exe");
                 //生成临时文件
                 RandomAccessFile raf = new RandomAccessFile(file, "rwd");
                 //设置临时文件的大小
                 raf.setLength(length);
                 raf.close();
                 //计算出每个线程应该下载多少字节
                 int size = length / ThreadCount;

                 for (int i = 0; i < ThreadCount; i++) {
                     //计算线程下载的开始位置和结束位置
                     int startIndex = i * size;
                     int endIndex = (i + 1) * size - 1;
                     //如果是最后一个线程，那么结束位置写死
                     if(i == ThreadCount - 1){
                         endIndex = length - 1;
                     }
 //                    System.out.println("线程" + i + "的下载区间是：" + startIndex + "---" + endIndex);
                     new DownLoadThread(startIndex, endIndex, i).start();
                 }
             }
         } catch (Exception e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
     }

 }
 class DownLoadThread extends Thread{
     int startIndex;
     int endIndex;
     int threadId;

     public DownLoadThread(int startIndex, int endIndex, int threadId) {
         super();
         this.startIndex = startIndex;
         this.endIndex = endIndex;
         this.threadId = threadId;
     }

     @Override
     public void run() {
         //再次发送http请求，下载原文件
         try {
             File progressFile = new File(threadId + ".txt");
             //判断进度临时文件是否存在
             if(progressFile.exists()){
                 FileInputStream fis = new FileInputStream(progressFile);
                 BufferedReader br = new BufferedReader(new InputStreamReader(fis));
                 //从进度临时文件中读取出上一次下载的总进度，然后与原本的开始位置相加，得到新的开始位置
                 startIndex += Integer.parseInt(br.readLine());
                 fis.close();
             }
             System.out.println("线程" + threadId + "的下载区间是：" + startIndex + "---" + endIndex);
             HttpURLConnection conn;
             URL url = new URL(MultiDownload.path);
             conn = (HttpURLConnection) url.openConnection();
             conn.setRequestMethod("GET");
             conn.setConnectTimeout(5000);
             conn.setReadTimeout(5000);
             //设置本次http请求所请求的数据的区间
             conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);

             //请求部分数据，相应码是206
             if(conn.getResponseCode() == 206){
                 //流里此时只有1/3原文件的数据
                 InputStream is = conn.getInputStream();
                 byte[] b = new byte[1024];
                 int len = 0;
                 int total = 0;
                 //拿到临时文件的输出流
                 File file = new File("QQPlayer.exe");
                 RandomAccessFile raf = new RandomAccessFile(file, "rwd");
                 //把文件的写入位置移动至startIndex
                 raf.seek(startIndex);
                 while((len = is.read(b)) != -1){
                     //每次读取流里数据之后，同步把数据写入临时文件
                     raf.write(b, 0, len);
                     total += len;
 //                    System.out.println("线程" + threadId + "下载了" + total);

                     //生成一个专门用来记录下载进度的临时文件
                     RandomAccessFile progressRaf = new RandomAccessFile(progressFile, "rwd");
                     //每次读取流里数据之后，同步把当前线程下载的总进度写入进度临时文件中
                     progressRaf.write((total + "").getBytes());
                     progressRaf.close();
                 }
                 System.out.println("线程" + threadId + "下载完毕-------------------小志参上！");
                 raf.close();

                 MultiDownload.finishedThread++;
                 synchronized (MultiDownload.path) {
                     if(MultiDownload.finishedThread == MultiDownload.ThreadCount){
                         for (int i = 0; i < MultiDownload.ThreadCount; i++) {
                             File f = new File(i + ".txt");
                             f.delete();
                         }
                         MultiDownload.finishedThread = 0;
                     }
                 }

             }
         } catch (Exception e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
     }
 }