I am developer of internet payment gateway solution in Java, and sometimes I wonder if I could/should have done something better.
Currently system works as follows:
System is receiving requests in form of html POST request to, lets say, confirm.xhtmlThere is some filter mappings for confirm.xhtml. In doFilter method there are some validations of request. ie. is merchant active, are required parameters present in POST parameters and so on.If request is valid, html page is displayed. This is very simple html page which consists of one form with fields like card number, card exp. date, customer name, surname, etc.When customer fills the form, message for authorizing host is created and sent via tcp socket connection (proprietary protocol).While system waits response from authorizing host, loading page is displayed to customer.When response from host is received, customer is redirected back to merchant site. This is html POST request with parameters like response message, approval code, and some other data relevant to specific implementation.
This is very general description of current system, but I would like to hear how would You do it (or already did it). Specifically, would you use some framework or would that be overkill because this is only one html page? ORM or plain JDBC? What about session management, security, client side or server side validations ... ?
I am aware that this question is very general, but I want to hear how would you approach to designing of such a system from the ground up.