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();

         }

     }

 }