Java多線程下載文件實例

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;


public class FileDownLoadTest {
    
    
     private static final int TCOUNT = 10;
    
     private CountDownLatch latch = new CountDownLatch(TCOUNT);

     private long completeLength = 0;
    
     private long fileLength;
     /**
     * @param args
     * @throws Exception
     */
     public static void main(String[] args) throws Exception {
         
          long begin = System.currentTimeMillis();
          new FileDownLoadTest().download("http://test1.com");
          System.out.println(System.currentTimeMillis() - begin);
     }
    
    
     public void download(String address) throws Exception{
          ExecutorService service = Executors.newFixedThreadPool(TCOUNT);
          URL url = new URL(address);
          URLConnection cn = url.openConnection();
          cn.setRequestProperty("Referer", "http://www.test.com");
          fileLength = cn.getContentLength();
          long packageLength = fileLength/TCOUNT;
          long leftLength = fileLength%TCOUNT;
          RandomAccessFile file = new RandomAccessFile("test.rar","rw");
          //計算每個線程請求文件的開始和結束位置
          long pos = 0;
          long endPos = pos + packageLength;
          for(int i=0; i<TCOUNT; i++){
               if(leftLength >0){
                    endPos ++;
                    leftLength--;
               }
               service.execute(new DownLoadThread(url, file, pos, endPos));
               pos = endPos;
          }
          latch.await();
     }
    
     class DownLoadThread implements Runnable{
         
          private URL url;
          private RandomAccessFile file;
          private long from;
          private long end;
         
          DownLoadThread(URL url, RandomAccessFile file, long from, long end){
               this.url = url;
               this.file = file;
               this.from = from;
               this.end = end;
          }
         
         
          public void run() {
               long pos = from;
               byte[] buf = new byte[512];
               try {
                    HttpURLConnection cn = (HttpURLConnection) url.openConnection();
                    cn.setRequestProperty("Range", "bytes=" + from + "-" + end);
                    if(cn.getResponseCode() != 200 && cn.getResponseCode()!=206){
                         run();
                         return;
                    }
                    BufferedInputStream bis = new BufferedInputStream(cn.getInputStream());
                    int len ;
                    while((len = bis.read(buf)) != -1){
                         synchronized(file){
                              file.seek(pos);
                              file.write(buf, 0, len);
                         }
                         pos += len;
                         completeLength +=len;
                         System.out.println(completeLength * 100 /fileLength + "%");
                    }
                    cn.disconnect();
                    latch.countDown();
               } catch (IOException e) {
                    e.printStackTrace();
                   
               }
          }
     }
}