java-patterns

The Stream API provides functional operations to filter, map, and aggregate collections efficiently. Use `filter()` to select elements, `map()` to transform them, and terminal operations like `collect()` to gather results—this approach is more readable and maintainable than nested loops, especially for complex data transformations in Java 17+.

Optional wraps potentially null values and replaces null checks with explicit methods like `isPresent()`, `orElse()`, and `ifPresent()`. This pattern prevents NullPointerExceptions, makes intent clear, and is the idiomatic approach for Java 17+ codebases to manage nullable data safely.

Constructor injection passes dependencies as parameters to a class constructor, making them immutable and testable. Spring automatically wires beans into constructors, eliminating the need for field injection and reducing coupling—this pattern is the modern best practice for Spring projects.

Yes. Spring's `@ControllerAdvice` and `@ExceptionHandler` annotations create global exception handlers that centralize error management across all controllers. This approach ensures consistent error responses, simplifies testing, and decouples exception logic from business code.

Use JUnit for unit tests with Mockito to mock dependencies, and Spring Boot's `@SpringBootTest` for integration tests. This combination isolates business logic, verifies service behavior, and validates Spring configuration—essential for comprehensive test coverage in modern Java applications.

Records create immutable data classes with minimal boilerplate for simple value holders. The Builder pattern suits complex objects with many optional fields, enabling readable construction and validation. Together, they modernize data modeling in Java 17+ while improving maintainability.