Check the file existence on the client side of GWT

I want to check the file existence of the client side of GWT, by using FileUpload and FormPanel. Since it is not possible to use java.io.File on the client side, does开发者_如何学JAVA anybody know how to do this?

Thanks in advance! Ike

It is not possible to check in javascript in the browser, whether a file exists or not. A file upload form does not give you the path to the file it is uploading (otherwise, it'd be a security hole!).

There is no reason why the browser needs to check the client side's file system.

An alternative would be either to use a java applet, and get the appropriate certificates/user permission so that it can read off disk, or some such browser plugin that also can perform disk reads (read: activeX plugins for IE)