当年一个简单可用的多线程断点续传类

代码如下：

package com;

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

/**
*这个类已经实现了多线程断点下载的功能，每次运行都会从进度文件中读取进度接着下，下完了会把进度文件删除掉
*/
public class MultiDownload {
    static int threadCount = 3;
    static int finishedThread = 0;
    //这个地址对吗
    static String path = "http://192.168.3.14:8080/EasyDownload/download.do";
    
    public static void main(String[] args) {
        
        try{
            URL url = new URL(path);
            HttpURLConnection conn= (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("GET");//get方式可以下载吗?
            conn.setConnectTimeout(5000);
            conn.setReadTimeout(5000);
            if(conn.getResponseCode()==200){
                int length = conn.getContentLength();
                File file = new File("a.exe");
                RandomAccessFile raf = new RandomAccessFile(file,"rwd");
                raf.setLength(length);
                raf.close();
                int size = length/MultiDownload.threadCount;
                
                for(int i=0;i<threadCount;i++){
                    int startIndex = i*size;
                    int endIndex = (i+1)*size-1;
                    if(i==threadCount-1){
                        endIndex = length-1;
                    }
                    
                    new DownloadThread(startIndex, endIndex, i).start();
                }
                
            }
        }catch(Exception e){
            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() {
        int total = 0;
        //再次发送请求,下载
        try{
            File progressFile = new File(threadId+".txt");
            if(progressFile.exists()){//如果存在txt文件
                FileInputStream fis = new FileInputStream(progressFile);
                BufferedReader br = new BufferedReader(new InputStreamReader(fis));
                int numberInTxt= Integer.parseInt(br.readLine());
                startIndex +=numberInTxt;
                total = numberInTxt;//total必须要在这里给它赋值,不然就不对了
                fis.close();
                br.close();
            }
            System.out.println(threadId+"开始:"+startIndex+"结束:"+endIndex);
            URL url = new URL(MultiDownload.path);
            HttpURLConnection conn= (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("GET");//get方式可以下载吗?
            conn.setConnectTimeout(5000);
            conn.setReadTimeout(5000);
            //看好了!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
            conn.setRequestProperty("Range", "bytes="+startIndex+"-"+endIndex);
            if(conn.getResponseCode()==206){
                InputStream is = conn.getInputStream();
                byte[] b = new byte[1024];
                int len = 0;
                
                
                File file = new File("a.exe");
                RandomAccessFile raf = new RandomAccessFile(file,"rwd");
                raf.seek(startIndex);//这句很重要!!!!!!!!!!!!!!
                while((len = is.read(b))!=-1){
                    raf.write(b,0,len);
                    total+=len;
                    if(total%1000 == 0){
                        System.out.println("线程"+threadId+"下载了"+total);
                    }
                    //生成临时文件
                    RandomAccessFile progressRaf = new RandomAccessFile(progressFile,"rwd");
                    progressRaf.write((""+total).getBytes());
                    progressRaf.close();
                }
                System.out.println("线程"+threadId+"下载完毕--------------");
                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){
            e.printStackTrace();
        }
        
    }
}