CashFlowz 💸 💸

Table of Contents

• Introduction
• API Documentation
• MoneyTransfer Microservice
• Notifications Microservice
• App Events
• Docker Guidelines

Introduction

CashFlowz is a Java-based microservices application for money transfers. It features an idempotent API and uses event-driven architecture for asynchronous communication between services.

API Documentation

Power-up the application (preferably with Docker) and visit "http://localhost:8080/api/swagger-ui/index.html" to explore endpoints of the app and read the API documentation! 😊

MoneyTransfer Microservice

Architecture

The moneytransfer REST microservice architecture follows a domain-driven design pattern.

Presentation Layer

Includes the endpoints and their Swagger documentation (MoneyTransferAPIController).

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Application Layer

Services:

• GetTransferService: retrieves transfers.

• GetAccountService: retrieves bank accounts.

• MoneyTransferService: performs the money transfer operation.

• CurrencyExchangeService: Gets the exchange rates from third party API (provided by https://freecurrencyapi.com/) using CurrencyExchangeDao. Performs currency exchange for a given rate and amount.

• TransferRequestService: gets, creates and completes transfer requests.

Aspects:

• IdempotentTransferAspect: An @Around aspect providing the functionality for idempotent transfer requests. It publishes a Kafka consumer topic for sending transfer notifications.

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Domain Layer

The Account entity represents a bank account with the following properties:

Field	Description
account_id	Unique identifier of the Account
owner_name	Owner name
balance	Account balance
currency	Currency of the Account
created_at	Creation date.

The Transfer entity represents a financial transfer between two accounts:

Field	Description
transfer_id	Unique identifier of the Transfer.
source_account_id	ID of the account sending the funds
target_account_id	ID of the account receiving the funds
amount	The transfer amount
currency	Transfer currency

The TransferRequest entity represents a transfer request:

Field	Description
transfer_request_id	Unique identifier of the TransferRequest
source_account_id	ID of the account sending the funds
target_account_id	ID of the account receiving the funds
amount	The transfer amount
transfer_request_status	The status of a TransferRequest
transfer	the associated Transfer of a completed TransferRequest
http_status	http status of a completed TransferRequest
info_message	includes the exception message or a success message

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Persistence Layer

Includes all (JPA) repositories and Data Access Objects (DAOs).

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Exception Handling & Logging

Using @ControllerAdvice for exception handling and logging.

Testing

Unit and integration tests with Junit-5 and @TestContainers.

Acceptance Criteria

• AC 1: Happy path
• AC 2: Insufficient balance
• AC 3: Transfer in the same account
• AC 4: Source/target account does not exist

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Notifications Microservice

The microservice features a Kafka consumer subscribed to the notification topic. This consumer listens for TransferCompletedEvent events and sends a transfer notification (log) message.

The TransferNotificationsService includes the logic for sending a transfer notification.

Testing

Unit and integration tests with Junit-5.

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App Events

The money transfer and notifications microservices communicate asynchronously with events (TransferCompletedEvent) using Kafka with Redpanda.

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Docker Guidelines

Build the project using Maven and let the magic ✨ happen by executing:

docker compose up --build

That's all you need, everything is set up for you :)

You can of course play with whatever database/cache/migration tool you like (I use Postgres, Redis and Flyway) by modifying the docker-compose.yml file.

Have fun!