How do i integrate paypal in my website? Java

I want to integrate paypal in my java web application. I saw that they offer many methods to accomplish this. 开发者_StackOverflow社区But i want my visitors to remain on my site only. My friend told me that Paypal offers webservice. But i can't seem to find any documentation on Paypal site. If anybody could help me with this, i would be really very grateful. Please offer me the relevant links on Paypal where i could read and get my things done.

Secondly, my friend also told me that we need to give location to paypal where my visitors would be redirected once paypal payment is complete. But i am confused. I am working on localhost. How would Paypal know about my localhost?

I have already created my sandbox testing account. What should be my next step. Please explain me in detail. I don't know anything about Paypal. Once i created a demo application of Express checkout where they give a simple button of Pay Now and on clicking on it shopping cart etc appears. But now i want my visitors to stay on same website.

Thanks in advance :)

Website Payments Standard:

https://www.x.com/community/ppx/wps

PayPal Tools for Developers:

https://www.x.com/community/ppx/dev-tools