Paypal's IPN in Wicket application

Question

I am building Wicket based web application with Paypal's "Buy now" buttons implemented. The functionality I need is to allow users download the file only when the transaction was verified. What I don't really understand is how to implement the IPN in the Wicket application. Before start coding, i need to know the basic theory behind it.

So what would be the steps to verify the payment using Paypal's IPN in Wicket application? Could "Success" and "IPN callback" pages be the same page?

Answer 1

IPN is a callback from paypal to notify merchant about mixed types of changes. The IPN listerner (your page) has to implement its protocol described on https://developer.paypal.com/webapps/developer/docs/classic/ipn/integration-guide/IPNIntro/

Citation: The action to take when your listener is notified of an event are application-specific. Here are some common actions applications take in response to IPN messages:

Trigger order fulfillment or enable media downloads
Update a list of customers
Update accounting records
Create specialized "to do" lists

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Success payment page is a page there is client browser redirected after a successful payment.

The result is that success payment page is called once or none at a single payment depending on its result. The IPN listener can be call anytime, even though no payment is currently in process!

As shown on an image in the link, the IPN callback is destiny to process mixed background operations. E.g. store given results into your database, etc.