Payment Processing Sample Project

This is a sample payment processing project I made as a homework assignment during the interview for a backend developer role for one of the banks in Baltic states. It exposes three endpoints:

• create a payment
• cancel a payment
• query payments by status and amount

The project is built using Java 21 and Spring Boot 3 with a Postgres database.

Run the service with docker compose

To run the service locally, run the following docker compose command from the root of the project directory:

docker compose up --build

The web service will be available on port 8083. Navigate to http://localhost:8083/swagger-ui.html address to open the Swagger documentation.

Run the service within IDE (preferably IntelliJ IDEA)

Locate the TestPaymentProcessingApplication class under the src/test/java/io/plagov/payment_processing/ path and run it using the IDE runner. It will start the application itself along with a Postgres database inside the docker container. The service will start on the 8080 port (NB! make sure the port is available).

Test the application

Create a payment

To create a payment, send the payload of the following format to the POST endpoint: /api/v1/payments

{
  "amount": "EUR 150.25",
  "debtorIban": "EE382200221020145685",
  "creditorIban": "LT121000011101001000",
  "details": "test details"
}

or using curl:

curl -X POST http://localhost:8083/api/v1/payments \
  -H "Content-Type: application/json" \
  -d '{
    "amount": "EUR 150.25",
    "debtorIban": "EE382200221020145685",
    "creditorIban": "LT121000011101001000",
    "details": "test details"
  }'

Cancel payment

To cancel a payment, call the POST endpoint /api/v1/payments/{paymentId}/cancel (use an ID of the existing payment):

curl -X POST http://localhost:8083/api/v1/payments/3fa85f64-5717-4562-b3fc-2c963f66afa6/cancel

Query payments

Payments can be retrieved by the mandatory status query parameter and the following optional amount query params: isEqualTo, isGreaterThan and isLessThan. Available options for the status are: ACCEPTED and CANCELLED. The following example will search for payments with ACCEPTED status and amount more than 125.00:

curl -X GET "http://localhost:8083/api/v1/payments?status=ACCEPTED&isGreaterThan=125.00"

The endpoint will return an empty list if no payments are found.

Consumer country resolution

The application also tries to resolve the country of the API consumer and logs it. If the country resolution failed to succeed, an error will be logged, but it won't affect the running of the payment processing application.

Notification service

The payment processing application sends an event notification to a fake notification service when a payment is created or when a payment is canceled.