1、http請求頭

2、http響應頭

PRagma: no-cache  以上三個頭一起用，就可以控制所有的瀏覽器不要緩存數據 

Range bytes=6-  實現斷點續傳

URL url=new URL("http://localhost:8080/myday04/1.txt");URLConnection conn=url.openConnection();conn.setRequestProperty("Range", "bytes=6-");InputStream in=conn.getInputStream();byte[] buffer=new byte[1024];int len=0;FileOutputStream out=new FileOutputStream("D://1.txt",true);while((len=in.read(buffer))>0){out.write(buffer,0,len);}out.close();in.close();