"Mail a friend" without Spam

I stand and must make a "mail a friend" feature. The only requirement I have received is that it should be as close to spam-free as possible.

My framework is that I have jsp available (of course, with underlying web and app server - but it is not necessary to carry out the task?).

I've looked a bit online and found CFFormProtect (http://cfformprotect.riaforge.org), which unfortunately makes use of Cold Fusion. I would rather stick to jsp, where possible. Someone who is familiar with a similar extension? Whether it is open source or cost money is no problem (in other words, in real borders :)).

I've also looked a bit on captcha. It seems I will give a bad user experience, so I would prefer to avoid. Charging the user to enter his own mail and then confirm it is also a possibility, but also one I would rather avoid.

All ideas and the like is more than welcome.

Captcha has been proven standard solution!

There is captcha solutions for JSP.

It will link to you is so unusual that I do not think that you can find a ready
solution. But most of the items are relatively easy to code.

If I have to be honest I am not come forward with what the solution should be. I think I leave it to the store to decide what they would ideally like to see.

If you would want points simply toss a response :)