多线程下载辅助类实现

如需转载，必须注明转自： http://blog.csdn.net/xiazdong/article/details/7738298

使用声明：

类名：MultiThreadDownloadUtil

API：

(1)download(String path,int count);

path：文件URL；

count：线程数量；

 

 package org.xiazdong.multidownload.util;

 import java.io.File;
 import java.io.InputStream;
 import java.io.RandomAccessFile;
 import java.net.HttpURLConnection;
 import java.net.URL;


 public class MultiThreadDownloadUtil{
     private static int filesize;
     private static int block;
     private static String filename;
     private static int downloadsize;
     private class MyThread extends Thread{
         private int i;          //线程ID
         private String path;    //下载文件的URL

         public MyThread(int i, String path) {
             this.i = i;
             this.path = path;
             downloadsize = 0;
         }
         @Override
         public void run() {
             try{
                 System.out.println("线程"+(i+1)+"开始下载");
                 //1.打开文件，并定位位置
                 RandomAccessFile raf = new RandomAccessFile(new File(filename), "rwd");
                 raf.seek(i*block);          //定位到此线程要负责下载的位置
                 int start = i*block;
                 int end = (i+1)*block-1;
                 //2.连接服务器
                 URL url = new URL(path);
                 HttpURLConnection conn = (HttpURLConnection)url.openConnection();
                 conn.setRequestMethod("GET");
                 conn.setRequestProperty("range", "bytes="+start+"-"+end);   //发出请求头

                 if(conn.getResponseCode()==206){        //注意：分段下载的返回码为206，而不是200
                     InputStream in = conn.getInputStream();
                     int length = 0;
                     byte[]data = new byte[1024];
                     while((length=in.read(data))!=-1){
                         raf.write(data,0,length);       //写入本地文件
                     }
                 }
                 //显示下载进度
                 downloadsize += (end-start);
                 System.out.println("已下载"+downloadsize/1024.0+"k,共"+filesize/1024.0+"k");
                 //3.关闭文件
                 raf.close();
                 System.out.println("线程"+(i+1)+"结束下载...");
             }
             catch(Exception e){
                 e.printStackTrace();
             }
         }
     }
     /**
      * 下载文件
      * @param path          URL
      * @param threadcount   线程数
      * @throws Exception
      */
     public static void download(String path,int threadcount) throws Exception{
         filename = path.substring(path.lastIndexOf('/')+1);
         filesize = getFileSize(path);
         block = getBlockSize(filesize,threadcount);
         createLocalRandomFile(filesize);
         MultiThreadDownloadUtil mdu = new MultiThreadDownloadUtil();
         for(int i=0;i<threadcount;i++){
             mdu.new MyThread(i,path).start();
         }
     }
     /**
      * 创建一个本地文件，并设置文件的大小
      * @param filesize
      * @throws Exception
      */
     private static void createLocalRandomFile(int filesize) throws Exception {
         RandomAccessFile raf = new RandomAccessFile(new File(filename), "rwd");
         raf.setLength(filesize);
         raf.close();
     }
     /**
      * 根据文件总大小和线程数求出每个线程要下载的数据量
      * @param filesize
      * @param threadcount
      * @return
      */
     private static int getBlockSize(int filesize, int threadcount) {
         return filesize%threadcount==0?filesize/threadcount:(filesize/threadcount+1);
     }
     /**
      * 求出文件总大小
      * @param path
      * @return
      * @throws Exception
      */
     private static int getFileSize(String path) throws Exception{
         URL url = new URL(path);
         HttpURLConnection conn = (HttpURLConnection)url.openConnection();
         conn.setRequestMethod("GET");
         if(conn.getResponseCode()==200){
             return conn.getContentLength();
         }
         else{
             return 0;
         }
     }
 }

 

 

测试类：

 package org.xiazdong.download;

 import org.xiazdong.multidownload.util.MultiThreadDownloadUtil;


 public class MultiThreadDownloader {

     public static void main(String[] args) throws Exception {
         int threadCount = 3;    //指定线程数量
         String path = "http://dlc2.pconline.com.cn/filedown_61761_6694063/drivethelife2010_pconline_setup.exe"; //指定下载文件路径
         MultiThreadDownloadUtil.download(path, threadCount);
     }
 }

将此文件下载到工程目录后，运行可用；