JAVA的HTTP多线程下载程序

JAVA的HTTP多线程下载程序。自己教学中使用的一段程序。

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1. public class DownloadNetTest { private File fileOut;
2. private URL url; private long fileLength=0;
3. //初始化线程数 private int ThreadNum=5;
4. public DownloadNetTest(){ try{
5. System.out.println("正在链接URL"); url=new URL("http://211.64.201.201/uploadfile/nyz.mp3");
6. HttpURLConnection urlcon=(HttpURLConnection)url.openConnection(); fileLength=urlcon.getContentLength();
7. if(urlcon.getResponseCode()>=400){ System.out.println("服务器响应错误");
8. System.exit(-1); }
9. if(fileLength<=0) System.out.println("无法获知文件大小");
10. //打印信息 printMIME(urlcon);
11. System.out.println("文件大小为"+fileLength/1024+"K"); //获取文件名
12. String trueurl=urlcon.getURL().toString(); String filename=trueurl.substring(trueurl.lastIndexOf('/')+1);
13. fileOut=new File("D://",filename); }
14. catch(MalformedURLException e){ System.err.println(e);
15. } catch(IOException e){
16. System.err.println(e); }
17. init(); }
18. private void init(){ DownloadNetThread [] down=new DownloadNetThread[ThreadNum];
19. try { for(int i=0;i<ThreadNum;i++){
20. RandomAccessFile randOut=new RandomAccessFile(fileOut,"rw"); randOut.setLength(fileLength);
21. long block=fileLength/ThreadNum+1; randOut.seek(block*i);
22. down[i]=new DownloadNetThread(url,randOut,block,i+1); down[i].setPriority(7);
23. down[i].start(); }
24. //循环判断是否下载完毕 boolean flag=true;
25. while (flag) { Thread.sleep(500);
26. flag = false; for (int i = 0; i < ThreadNum; i++)
27. if (!down[i].isFinished()) { flag = true;
28. break; }
29. }// end while System.out.println("文件下载完毕，保存在"+fileOut.getPath() );
30. } catch (FileNotFoundException e) { System.err.println(e);
31. e.printStackTrace(); }
32. catch(IOException e){ System.err.println(e);
33. e.printStackTrace(); }
34. catch (InterruptedException e) { System.err.println(e);
35. } }
36. private void printMIME(HttpURLConnection http){ for(int i=0;;i++){
37. String mine=http.getHeaderField(i); if(mine==null)
38. return; System.out.println(http.getHeaderFieldKey(i)+":"+mine);
39. } }
40. public static void main(String[] args) { DownloadNetTest app=new DownloadNetTest();
41. } }