Java Functional Exception handling Best Practices

Identify and apply functional exception handling best practices in Java to improve error clarity, maintainability, and performance by eliminating exception overuse in favour of monadic error types.

Prerequisites: Run ./mvnw validate or mvn validate before applying any changes. If validation fails, stop immediately — do not proceed until the project is in a valid state. Also confirm the VAVR dependency (io.vavr:vavr) and SLF4J are present when introducing Either types.

Core areas: Optional<T> for nullable values over throwing NullPointerException or NotFoundException, VAVR Either<L,R> for predictable business-logic failures, CompletableFuture<T> for async error handling, sealed classes and records for rich error type hierarchies with exhaustive pattern matching, enum-based error types for simple failure cases, functional composition with flatMap/map/peek/peekLeft for chaining operations that can fail, structured logging at appropriate severity levels (warn/info for business failures, error for system failures), checked vs unchecked exception discipline, and exception chaining with full causal context when exceptions are unavoidable.

Scope: The reference is organized by examples (with good/bad code patterns) for each core area. Apply recommendations based on applicable examples; validate compilation before changes and run ./mvnw clean verify or mvn clean verify after applying improvements.

Before applying changes: Read the reference for detailed good/bad examples, constraints, and safeguards for each functional exception handling pattern.

Reference

For detailed guidance, examples, and constraints, see references/143-java-functional-exception-handling.md.