title: google app engine showing dialog box
body: <p>I am building a google app engine project.
  Right now I am trying to code in servlet file so that it can show dialog box.
  So when I start the app, it first goes to main page and there is a button.
  If I click the button, my servlet will handle the event. And I would like to ask how can I make my servlet show the dialog box in web page. Thank you very much</p>