detecting if a file is ready and serving it for download

I have a Spring MVC web application that is generating a report on the server, once the report is generated, I need to enable a button that allows the user to download it. I am not sure how to go about doing this.

I figured that I will have to spawn off a thread that will just keep checking for the existence of the file and use javascript (jQuery or pr开发者_JAVA百科ototype most likely) to handle the UI elements, but I'm just not sure how to tie these all together.

There are no threads in Javascript. Instead you'll set a timeout to do the polling. The polling would take the form of a URL that will respond with some sort of "ready" indicator when the file is ready. If the file is not ready, then the AJAX success handler will start another timeout. When the server says it's ready, your Javascript handler will make the button visible and no further polling will be necessary.

Check this example here http://forum.springsource.org/showthread.php?t=70489 and let know if it works

You could use some type of messaging on the server that tells the client when the file is ready e.g. we us a table for all report requests and the server writes the status into the table and the client is then asking for the status of the report job with an AJAX call every few seconds.