Payment system application programming interface.
Electronic payment generic library API
Java Client Library for Braintree Payments Gateway
Authorize.Net SDK includes standard payments, recurring billing, and customer profiles.
The PayPal Adaptive Payments SDK provides Java APIs to create, process and manage simple and complex (parallel and chained) payments, and pre-approvals using the Adaptive Payments API.
This Java library contains classes that allows you to do payments using Yandex.Money public API.