Simple Banking API JAVA

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A RESTful API for a simple banking system, built with Spring Boot, heavily focused on best practices like Clean Architecture, SOLID principles, and Clean Code.

Technologies and Tools

• Java 17
• Spring Boot 3.2.5 (Web, Data JPA, Validation)
• H2 Database (In-memory for DEV, persistent for PROD)
• Springdoc OpenAPI (Swagger) for interactive documentation
• Lombok to reduce boilerplate
• JUnit 5 / Mockito for unit testing
• TestRestTemplate / @SpringBootTest for integration testing
• JPA Auditing for automatic creation/modification timestamps tracking

Features and Business Rules

• Clients: Account creation associated with client registration; custom CPF validation; paginated listing (Pageable).
• Accounts: Support for Account Types (CHECKING/SAVINGS).
• Operations: Withdrawals, Deposits, and Transfers with atomic balance calculations.
• Transactions: Automatic and auditable recording of movements; paginated bank statements.
• Error Handling: Global Exception Handler (@ControllerAdvice) managing rich messages to the client, @Valid field validations, etc.
• Structured Logging: Systemic interception with SLF4J at every transactional step.

Architectural Patterns and Design

• Layer Segregation: Code divided clearly into domain, application, presentation, and infrastructure layers.
• "Tell, Don't Ask": Domain business logic (e.g., depositing and withdrawing balance) is cohesively encapsulated directly inside the relational Conta (Account) class.
• DTOs & Records: Protection of the transactional application layer using isolated, immutable contracts (Request/Response) via Java Records.

How to Run (Locally - DEV)

The application has two main active profiles configured: dev (default) and prod.

1. Clone the repository
2. Run the Maven command at the root:

   mvn spring-boot:run

3. The API will be available at http://localhost:8080/api.

Swagger UI (DEV Only)

• Access http://localhost:8080/docs to inspect, generate mock requests, and freely interact with the endpoints.

H2 Database Console

• Access http://localhost:8080/h2-console
• Username: sa
• Password: (empty)
• JDBC URL: jdbc:h2:mem:bancodb

How to Run the Tests

The tests for this API consist of:

• Unit Tests: Tests running with injected independent mocks from Mockito, simulating infrastructure contracts (repositories) to ensure logic conditions and @Throw Exceptions.
• Integration Tests: Randomized web environment that builds the full Spring container and executes tests calling endpoints directly on Controllers using TestRestTemplate, verifying database persistence integrity and precise HttpStatus behaviors.

 mvn test

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This project was completed as an incremental proof of concept involving 30 meticulous steps of structural evolution and corporate backend best practices.