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(); 
  } 
   
 }; 
}