How to correctly implement account approving?

I'm working on a web-project on JavaEE6/SpringMVC. I need to send a user the email wich contains the URL which you need to approve your just created account. For instance

You're registered on `mysite.com`. To approve your account
please follow this link:
%SITE_URL%/approve=wuhber83724fi3u49f8g2h34otb34tbewjkrtb3iu4gt534b34

I don't know how to do this in an appropriate way. First of all, I'd like to know how to generate the value of approve code here? Might you provide a describing such an issue.