This Spring Boot Java project extends the simple-state-machine project to make the processors asynchronous and non-blocking.
The first step in using the framework is to configure the state transitions. An online order processing system is considered as an example for the demo. The order processing system is assumed to have the following state transitions:
| Initial State | Pre-event | Processor | Post-event | Final State |
|---|---|---|---|---|
| DEFAULT | submit | OrderProcessor | orderCreated | PMTPENDING |
| PMTPENDING | pay | PaymentProcessor | paymentError | PMTERROREMAILPENDING |
| PMTERROREMAILPENDING | errorEmail | PaymentErrorEmailProcessor | pmtErrorEmailSent | PMTPENDING |
| PMTPENDING | pay | PaymentProcessor | paymentSuccess | PMTSUCCESSEMAILPENDING |
| PMTSUCCESSEMAILPENDING | successEmail | PaymentSuccessEmailProcessor | pmtSuccessEmailSent | COMPLETED |
where the PaymentProcessor is considered a long running process and made asynchronous and non-blocking. All other processors are assumed synchronous. The above state transitions are configured in Java enums, OrderState and OrderEvent.
The demo includes an OrderController with two APIs to test the following scenarios:
Build using:
$ ./gradlew build
Run using:
$ \gradlew bootRun
User submits an order
System responds with an order ID.
Log messages confirm the state transition.
$ curl -X POST http://localhost:8080/order/items
User submits an invalid payment for the order
System responds with a message "We are processing your payment. Please check your email for the order confirmation number."
System also sends an email with an error message.
Log messages confirm the state transition.
$ curl -X POST http://localhost:8080/orders/1e6092da-3bef-4377-8a02-5a4cb93f4a96/payment/0
User submits a valid payment for the order
System responds with a message "We are processing your payment. Please check your email for the order confirmation number."
System also sends an email with a success message.
Log messages confirm the state transition.
$ curl -X POST http://localhost:8080/orders/1e6092da-3bef-4377-8a02-5a4cb93f4a96/payment/1
User submits a valid payment for the order
System responds with a message "Order is completed for orderId=1e6092da-3bef-4377-8a02-5a4cb93f4a96."
No state transition occurs in this case.
$ curl -X POST http://localhost:8080/orders/1e6092da-3bef-4377-8a02-5a4cb93f4a96/payment/2
Interested readers can run the included Apache JMeter test plan to test for multiple simultaneous users placing orders and paying for the orders.
An improved version of this project is at: state-transitions-with-spring-integration
The technique used in this Java project can be easily adapted to front-end JavaScript UI applications. Here is an example for the TodoMVC UI application.
More info about this project is also available at: dzone