Integrate Java PayPal NVP API in Spring Framework.

I'm looking to handle the following scenario: 1. Registered user come to listing 2. Click on Buy Button 3. User will be taken to PayPal where he will be charged 4. The money user pays goes into "escrow hold" 5. Seller is notified that sale has been made that he/she will is charged fee via PayPal at the end of their monthly billing cycle. 6. Seller delivers. 7. Buyer releases the hold on funds to complete the order. OR 6a. Seller cancels the order 7a. System automatically refunds the charge and marks the order as canceled. 8a. Fee will be refunded to the Seller. OR 6b. Seller will perform partial refund. 7b. The system fill partially refund the customer. OR There is dispute and all special circumstances have to be accounted for. I don't know what this could be but you should as experienced developer in Java NVP PayPal SDK. Now monthly billing: When seller enables his/hers first listing for public they will be redirected to create CreateRecurringPaymentsProfile for their invoice monthly payments. Invoice totals will be calculated via internal system that will keep track of all the fees. Once a month the seller will be automatically charged the due on their invoice. The seller will have option to keep account balance in which case that will be charged first and the their PayPal account will be charged for the reminder of the due amount. There is already existing Spring Framework that is fully functional. There has been some attempts to do this but it requires solid experience with the PayPal Java API and Spring. The requirement will be to design necessary controllers and services to be used as beans in the spring framework. The presentation layer is written in Freemarker and handles only input, no business logic so copy and paste from [login to view URL] samples will not do. There will be no need to integrate the above into existing project. All is required is that you will take look at the exiting logic take out what you need, make separate simplified application that does not have DAO layer (simple comments like persist the transaction here will be enough). But the simplified application has to fully work with paypal sandbox and there have to test case created. Either via documentation or through JUnit, Selenium and mock objects.