Java Security

Hi,

Overview
My request is part of a user registration implementation that I'm undertaking. When a user registers at the website, he/she is sent a secure link via email. Once this link is clicked, the account is activated.

Query
How do I generate unique secure links for each user, which once clicked will recognize the user and activate the account?

Idea
One way will be to just add the user id that is generated as part of the registration process to the url and move forward

Questions
1. Is my initial idea a good one, is it secure enough?
2. Are there any open source packages that will help me do what I intend to do?
3. Any articles/posts that might be of help?

I've tried google, but could not find anything other than http://www.servletsuite.com/servlets/securelinkflt.htm

Thanks,
Dev