How to handle an online payment handled using Web Services safely?

Disclaimer: I only have a very basic understanding of how Web Services work and don't know much about advanced WS topics such transactions, etc.

Let's pretend that I am developing an online store using Java EE, JPA, etc. Also let's pretend that I have a contract with an online payment processing provider to handle payments and they have provided me with a WS API.

Now let's pretend that a customer has placed an order. In a session bean (e.g. inside OrderSB.placeOrder) I have opened a transaction, saved an Order in the DB, and now I am making a call to the payment provider's WS API. It returns successfully (and I assume that by now my customer's account has been debited) but before I can save the Order's associated Payment (there's one-to-one relationship between Order and Payment) an exception occurs and my transaction is rolled back.

How is it possible to ensure that when such an exception happens, my customer's account is not debited? Or in other words either both of the WS call and OrderSB.placeOrder should complete successfully and commit or both of them should be rolled back together.

It's easy to roll back placeOrder if the WS call fails, but I don't know how I can roll back the开发者_运维问答 WS call after it returns.

Why don't you complete the placeOrder flow and do the WS call just if the first finished with success? Then as you say that is easy to rollback placeOrder, if errors appear in the second just rollback the first one. Or am I not understanding your question right?