Java Web Application with Payment Processing

I'm in need of a skilled software developer who specializes in Java to build a web application, the core feature being payment processing.

Key Requirements:
- A deep understanding of and proficiency in Java.
- Prior experience in developing web applications with payment processing functionalities.
- Understanding of security protocols related to online payments.

Your task will primarily involve designing and implementing a reliable payment processing system. Please provide examples of similar projects you've worked on previously. Only those with relevant experience need apply.