1 - you can't nest custom tags as attributes to other custom tags.
2 - when you press a key, it won't invoke the bean:write tag.
Java/JSP runs on server side, and produces an html page, which it sends to the browser.
Then you can start running javascript (and reacting to javascript events)
You only run
java again when you make a request (submit a form, click a link etc)
Basically you have to do this date formatting/validation in pure html/javascript.
Instead of passing the value, I would recommend passing the textfield itself using the "this" keyword.