Query MySQL Database Client Side

I am trying to validate that a username is unique on a registration form and would like to ve开发者_开发知识库rify the uniqueness of the username right after the client types it as opposed to performing this server side after the form has been submitted.

Should I collect a resultSet from the database, store it in an array and then pass this along to the jsp page in the form of a bean (I am using a model 2 design so the user passes through a servlet before arriving at the jsp page)? What if the array is very large? How do I bring this data into javascript?

Alternatively, is there a way to do the query using ajax and javascript all on the client side? Maybe its possible to somehow run the query in the background?

I am really just looking for some direction because I am clueless as to what to even begin researching something like this. Is this even a smart move, performance wise?

I'd use "AJAX" for this.

Here's one approach: set up a blur() handler on the username text field of your form. When the blur() method is invoked, you post the username to the backend code; it verifies it and returns some appropriate response. You then parse the response and change the CSS class on the username text field (e.g., turning it red) -- or do whatever else visually you want to do to indicate "username in use."

Either way, you've got to get the username from the client to the server for verification; you wouldn't want any mechanism which allowed the client to directly use the DB (think security/exploits/etc).

If you're not already familiar, check out jQuery (http://jquery.com/) to make your client-side life much easier.