tranxactive/J2PAY ? reverse-engineered prompt

Build me a Java library for handling payments through multiple gateways with one simple, consistent API.

I want to be able to create the same kind of request for things like authorize, capture, purchase, refund, recurring, and void, then send it to different gateways without rewriting all the payment logic each time. Please include support for common gateways like Authorize, NMI, Payeezy, Payflow Pro, BillPro, EasyPay, Checkout, Stripe, and Braintree, and make the request and response objects feel generic so the field names stay the same no matter which provider is used.

The main goal is to hide all the annoying differences between gateway parameter names and response formats, so things like customer info, card details, and transaction IDs come back in a standard way. Keep it as a reusable library, not a full app, and make it easy to plug into a Java project with clear examples in the docs. If you need to check current gateway docs online while implementing, go ahead and do that.