java多线程实现文件下载功能

package com.ldw.multilthreaddownload;  import java.io.File; import java.io.InputStream; import java.io.RandomAccessFile; import java.net.HttpURLConnection; import java.net.URL;  public class Multidownload {   static int ThreadCount = 3; //线程的个数  static String path = "http://192.168.0.102:8080/QQ.exe"; //确定下载地址  public static void main(String[] args) {   // TODO Auto-generated method stub      //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){     //获取到请求资源文件的长度     int length = conn.getContentLength();     File file = new File("QQ.exe");     //创建随机存储文件     RandomAccessFile raf = new RandomAccessFile(file, "rwd");     //设置临时文件的大小     raf.setLength(length);     //关闭raf     raf.close();     //计算出每一个线程下载多少字节          int size = length / Multidownload.ThreadCount;          for(int i = 0; i < Multidownload.ThreadCount; i ++){      //startIndex,endIndex分别代表线程的开始和结束位置      int startIndex = i * size;      int endIndex = (i + 1) * size - 1;      if(i == ThreadCount - 1){       //如果是最后一个线程，那么结束位置写死       endIndex = length -1;      }      System.out.println("线程" + i + "的下载区间是" + startIndex + "到" + endIndex);      new DownLoadThread(startIndex, endIndex, i).start(); //创建线程下载数据     }    }   } 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(){   //使用http请求下载安装包文件   URL url;   try {    url = new URL(Multidownload.path);    HttpURLConnection conn = (HttpURLConnection) url.openConnection();    conn.setRequestMethod("GET");    conn.setConnectTimeout(5000);    conn.setReadTimeout(5000);    //设置请求数据的区间    conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);    //请求部分数据的响应码是206    if(conn.getResponseCode() == 206){     //获取一部分数据来读取     InputStream is = conn.getInputStream();     byte[] b = new byte[1024];     int len = 0;     int total = 0;     //拿到临时文件的引用     File file = new File("QQ.exe");     RandomAccessFile raf = new RandomAccessFile(file, "rwd");     //更新文件的写入位置，startIndex     raf.seek(startIndex);     while((len = is.read(b)) != -1 ){      //每次读取流里面的数据，同步吧数据写入临时文件      raf.write(b, 0, len);      total += len;      System.out.println("线程" + threadId + "下载了" + total);     }     System.out.println("线程" + threadId + "下载过程结束===========================");     raf.close();    }   } catch (Exception e) {    // TODO Auto-generated catch block    e.printStackTrace();   }     }; }