Payment Workflow Documentation

This documentation provides a detailed explanation of the payment workflow created using Spring Batch and Resilience4j. The workflow handles external API calls with resilience mechanisms using Retry and CircuitBreaker for robust error management.

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General Workflow

The payment workflow consists of three main steps:

1. Initiate Payment (initiatePaymentStep)
2. Verify Payment (verifyPaymentStep)
3. Complete Payment (completePaymentStep)

These steps are executed sequentially, and each is wrapped with Resilience4j’s Retry and CircuitBreaker mechanisms to manage errors.

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Key Components of the Workflow

1. PaymentApiClient

PaymentApiClient simulates interactions with an external API during the payment workflow. The methods called during the workflow are:

• initiatePayment: Initiates the payment and returns a transaction ID.
• verifyPaymentStatus: Verifies the payment status and returns a random result for demonstration.
• completePayment: Completes the payment.

Each method simulates an external API call and follows specific error scenarios to test the resilience mechanisms.

2. Spring Batch Workflow Steps

Each step operates as a Tasklet and carries data through ExecutionContext. The steps work as follows:

1. initiatePaymentStep:

   • Simulates a failure on the first attempt to trigger the retry mechanism.
   • Retrieves a transactionId and saves it to the ExecutionContext.

2. verifyPaymentStep:

   • Verifies the payment status by calling the external API. If the status check fails, the Retry mechanism activates. If the failure rate reaches a certain threshold, the CircuitBreaker interrupts the process.
   • Marks the step as FINISHED if verification succeeds.

3. completePaymentStep:

   • Completes the payment and ends the workflow successfully if all conditions are met.

3. Error Handling with Resilience4j

The workflow employs Retry and CircuitBreaker mechanisms for error handling:

• Retry: Retries failed attempts a specified number of times to overcome temporary issues.
• CircuitBreaker: Stops operations if the failure rate reaches 50%, transitioning to an Open state. When wait-duration-in-open-state expires (e.g., 5 seconds), the CircuitBreaker moves to a Half-Open state to test the service again.

CircuitBreaker Calculation

The CircuitBreaker measures the failure rate over the last 10 calls. If the failure rate exceeds 50%, it switches to Open (open) mode and stops new calls for the wait-duration-in-open-state period. After this time, the CircuitBreaker moves to Half-Open mode and re-evaluates. If the next call succeeds, the CircuitBreaker returns to Closed mode; otherwise, it reopens.

4. Data Management with ExecutionContext

Spring Batch uses ExecutionContext to share data between steps:

• transactionId: Obtained in initiatePaymentStep and saved to ExecutionContext for subsequent use.

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Workflow Scenario

The workflow includes specific failure simulations and resilience mechanisms for each step:

1. initiatePaymentStep:

   • The first call is simulated to fail, triggering the retry mechanism.
   • Retrieves the transactionId and saves it to ExecutionContext once successful.

2. verifyPaymentStep:

   • Checks the payment status. If it fails, the retry mechanism activates. If the failure persists, the CircuitBreaker interrupts the process.
   • If successful, the step is marked as FINISHED.

3. completePaymentStep:

   • Completes the payment, ending the workflow if all prior steps were successful.

Independent Workflows in a foreach Loop

In a foreach loop, each customer’s workflow can run as an independent job instance:

• Independent Transactions: Each job operates independently, so a failure in one job does not affect the others.
• Parallel Execution: Each customer’s workflow can execute in parallel, allowing high concurrency.

for (Customer customer : customers) {
    JobParameters jobParameters = new JobParametersBuilder()
            .addString("customerId", customer.getId().toString())
            .addDate("runDate", new Date())
            .toJobParameters();

    jobLauncher.run(paymentJob, jobParameters);
}

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Error and Transaction Management

Error and transaction handling are managed as follows:

• Retry Mechanism: Manages transient errors, retrying failed attempts and ensuring process continuity.
• CircuitBreaker: Stops the process if the error rate exceeds 50%. After a specified time, it re-evaluates the service.
• Transaction Management: Each step operates independently, so a failure in one step does not affect the others.

Step-by-Step Workflow

1. First Step (initiatePaymentStep):

   • Starts the payment initiation, simulating a failure on the first attempt. The retry mechanism attempts the call again.
   • Retrieves the transactionId and saves it to ExecutionContext once successful.

2. Second Step (verifyPaymentStep):

   • Attempts to verify payment status. If it fails, retry attempts are made. After repeated failures, the CircuitBreaker stops further attempts.
   • If successful, the step is marked as FINISHED.

3. Third Step (completePaymentStep):

   • Completes the payment and marks the workflow as successfully completed.

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foreach Loop Note on Independent Workflow Execution

Using a foreach loop, each job instance runs independently:

• No Infinite Loops: Each job completes independently, with each customer’s workflow ending without impacting others.
• Independent Transactions: Each job instance handles a separate customer transaction, allowing independent error handling.

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Summary: Spring Batch and Resilience4j Advantages

The combination of Spring Batch and Resilience4j provides several advantages:

• High Availability: Processes are resilient to transient errors, allowing workflows to complete successfully.
• Advanced Error Management: Retry and CircuitBreaker mechanisms offer flexibility and resilience.
• Independent Transaction Management: Each job instance operates independently, ensuring that a failure in one job does not affect others.

This documentation covers the complete structure of the payment workflow, its error-handling mechanisms, and data management strategies.