Web Browser Actions Java

I am trying to make a bot that will allow me to add an item to my amazon (or any other webstore) shopping cart. The problem that I am having is that I think it is too complicated for me to make the program ask for login info so I need to store it in the shopping cart without logging in. How can I do this? Can I do it through the console and then somehow open that browser session and complete my order?

Otherwise is it difficult to add a login item?

Thanks for any advice or tips leading me in the right direction