[置顶] java多线程下载文件

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

 public class MulThreadDownload {
     public static void main(String[] args) throws Exception {
         String path = "http://192.168.1.100:8080/Hello/Big.exe";
         new MulThreadDownload().download(path, 3);
     }

     /**
      * 下载文件
      *
      * @param path
      *            网络文件路径
      * @param threadSize
      *            线程数
      * @throws Exception
      */
     private void download(String path, int threadSize) throws Exception {
         URL url = new URL(path);
         HttpURLConnection connection = (HttpURLConnection) url.openConnection();
         connection.setRequestMethod("GET");
         connection.setConnectTimeout(5000);
         if (connection.getResponseCode() == 200) {
             int length = connection.getContentLength();// 获取网络文件长度
             File file = new File(getFileName(path));
             // 在本地生成一个长度与网络文件相同的文件
             RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
             accessFile.setLength(length);
             accessFile.close();

             // 计算每条线程负责下载的数据量
             int block = length % threadSize == 0 ? length / threadSize : length
                     / threadSize + 1;
             for (int threadId = 0; threadId < threadSize; threadId++) {
                 new DownloadThread(threadId, block, url, file).start();
             }
         } else {
             System.out.println("download fail");
         }
     }

     private class DownloadThread extends Thread {

         private int threadId;
         private int block;
         private URL url;
         private File file;

         public DownloadThread(int threadId, int block, URL url, File file) {
             this.threadId = threadId;
             this.block = block;
             this.url = url;
             this.file = file;
         }

         @Override
         public void run() {
             int start = threadId * block; // 计算该线程从网络文件什么位置开始下载
             int end = (threadId + 1) * block - 1; // 计算下载到网络文件什么位置结束
             try {
                 RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
                 accessFile.seek(start);  //从start开始

                 HttpURLConnection connection = (HttpURLConnection) url
                         .openConnection();
                 connection.setRequestMethod("GET");
                 connection.setConnectTimeout(5000);
                 //设置获取资源数据的范围，从start到end
                 connection.setRequestProperty("Range", "bytes=" + start + "-"
                         + end);
                 //注意多线程下载状态码是 206  不是200
                 if (connection.getResponseCode() == 206) {
                     InputStream inputStream = connection.getInputStream();
                     byte[] buffer = new byte[1024];
                     int len = 0;
                     while ((len = inputStream.read(buffer)) != -1) {
                         accessFile.write(buffer, 0, len);
                     }
                     accessFile.close();
                     inputStream.close();
                 }
                 System.out.println("第" + (threadId + 1) + "条线程已经下载完成");
             } catch (Exception e) {
                 e.printStackTrace();
             }
         }
     }

     /**
      * 获取文件名称
      *
      * @param path
      *            网络文件路径
      * @return
      */
     private String getFileName(String path) {
         return path.substring(path.lastIndexOf("/") + 1);
     }
 }