I\'m trying to find a java based API that wraps up the details of processing a credit card transaction or purchase via PayPal at a minimum, and other gateways as a plus in an IP
You can not get an API for payment gateway integration. You will have to write your own development for the processing with various payment gateways. For that you have to understand that which payment gateway gets which parameters and its requesting URL for requesting for the paymentgateway. You can get this information by varius payment gateway websites.
This url may helpful to you
For HDFC : http://www.hdfcbank.com/sme/sme-details?id=guzh6m0i
For Paypal : https://merchant.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=merchant/payment_gateway
Secure Pay : http://www.securepay.com.au/
techpro [ ICICI ] : http://forums.devarticles.com/asp-development-3/how-to-integrate-payseal-icici-payment-gateway-95329.html
Here you can also find the development APIs or the guidelines for the development that which parameters they will require for processing the requests.
Hope this may help you.
Enjoy !!!