title: how to generate a identified filename from url?
body: <p>Now I have to download a file whose url has known. I need to save it to SD card when download action finished. The problem is I should know whether the file is existed before downloading. So I plan to save the file with a identified filename which is generated from url. So when I get the url I can calculate his corresponding filename. Which algorithm should I use? </p>
  
  <p>BTW, JAVA is what I'm using.</p>
  
  <p>Maybe, I have not told my requirement clearly. Fetch the filename "abc.png" from url "www.yahoo.com/abc.png" is not what I need. Because "www.google.com/abc.png" results the same filename. I need to generate a unique filename from url.</p>