A very silly issue that could take lot of time for you to realize. Some times, very unlikely, Struts action executes multiple times when form gets submitted. This would happen only with the Firefox browser and not with the other browsers like Internet Explorer, Chrome etc. Very interesting, although this wouldn't effect any user functinalities. i.e.; if you're running you won't know that your struts action is invoking for multiple times unless you debug.

Why and when this happens

If you've a blank image tag inside the form tag which is going to be submitted on the Firefox then this issue would happen. This is because Firefox will try to find the image at the same path of your current URL when you've a blank img tags.

Be good to know the issues like this otherwise you would have to spend more time if it your turn.