Payment State Machine

This project is a practical example of implementing a payment processing state machine using the Java Framework Spring Boot and Spring Statemachine. It demonstrates how to model the lifecycle of a payment—from creation through pre-authorization and final capture—in a clean and state-driven way.

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Technology Stack

• Java 17
• Spring Boot
• Spring Statemachine
• Spring Data JPA
• H2 Database
• Maven
• JUnit 5 & Spring Test

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How the State Machine Works

The machine follows a two-step payment authorization flow. The states and transitions are managed based on specific events that represent the outcome of payment operations.

State Machine Diagram

The diagram below visually represents the entire flow of states and events described below.

Events and Transitions

1. Creation → Pre-Authorization:

   • The process begins when a PRE_AUTHORIZE event is sent.
   • This transitions the payment into the NEW state, ready for processing.

2. Pre-Authorization Outcome:

   • If the pre-authorization is successful, a PRE_AUTH_APPROVED event moves the state to PRE_AUTH. The funds are now on hold.
   • If the pre-authorization is declined, a PRE_AUTH_DECLINED event moves the state to PRE_AUTH_ERROR, which is a final failure state.

3. Final Authorization (Capture) Outcome:

   • From the PRE_AUTH state, an AUTHORIZE event is sent to capture the held funds.
   • If the capture is successful, an AUTHORIZED event transitions the state to AUTH, the final success state.
   • If the capture is declined, an AUTH_DECLINED event transitions the state to AUTH_ERROR, another final failure state.