126 Java Exception Handling

---
name: 126-java-exception-handling
description: Use when you need to apply Java exception handling best practices — including using specific exception types, managing resources with try-with-resources, securing exception messages, preserving error context via exception chaining, validating inputs early with fail-fast principles, handling thread interruption correctly, documenting exceptions with @throws, enforcing logging policy, translating exceptions at API boundaries, managing retries and idempotency, enforcing timeouts, attaching suppressed exceptions, and propagating failures in async/reactive code. This should trigger for requests such as Exception handling; Use try-with-resources in Java code; Create exception chaining in Java code; Apply fail-fast validation in Java code; Review Java exception taxonomy and propagation. Part of Plinth Toolkit
license: Apache-2.0
metadata:
  author: Juan Antonio Breña Moral
  version: 0.19.0
---
# Java Exception Handling Guidelines

Identify and apply robust Java exception handling practices to improve error clarity, security, debuggability, and system reliability.

**What is covered in this Skill?**

- Specific exception types instead of generic `Exception`/`RuntimeException`
- try-with-resources for automatic resource cleanup
- Secure exception messages that avoid information leakage
- Exception chaining to preserve full error context
- Early input validation with `IllegalArgumentException`/`NullPointerException`
- `InterruptedException` handling with interrupted-status restoration
- `@throws` JavaDoc documentation, fail-fast principle
- Structured logging with correlation IDs, avoiding log-and-throw duplication
- API boundary translation via centralized exception mappers
- Bounded retry with backoff for idempotent operations only
- Timeout enforcement with deadline propagation
- `Throwable#addSuppressed` for secondary cleanup failures
- Never catching `Throwable`/`Error`
- Observability via error metrics
- Failure propagation in async `CompletionStage` code

**Scope:** The reference is organized by examples (good/bad code patterns) for each core area. Apply recommendations based on applicable examples.

## Constraints

Before applying any exception handling changes, ensure the project compiles. If compilation fails, stop immediately — do not proceed until resolved. After applying improvements, run full verification.

- **MANDATORY**: Run `./mvnw compile` or `mvn compile` before applying any changes
- **SAFETY**: If compilation fails, stop immediately — do not proceed until the project is in a valid state
- **VERIFY**: Run `./mvnw clean verify` or `mvn clean verify` after applying improvements
- **BEFORE APPLYING**: Read the reference for detailed good/bad examples, constraints, and safeguards for each exception handling pattern

## When to use this skill

- Exception handling
- Use try-with-resources in Java code
- Create exception chaining in Java code
- Apply fail-fast validation in Java code
- Review Java exception taxonomy and propagation

## Workflow

1. **Compile project before exception-handling changes**

Run `./mvnw compile` or `mvn compile` and stop immediately if compilation fails.

2. **Read exception-handling reference**

Read `references/126-java-exception-handling.md` and identify applicable failure-handling and observability improvements.

3. **Apply exception-handling improvements**

Refactor to specific exceptions, safe resource handling, error translation, and consistent logging patterns.

4. **Verify with full build**

Run `./mvnw clean verify` or `mvn clean verify` after applying improvements.

## Reference

For detailed guidance, examples, and constraints, see [references/126-java-exception-handling.md](references/126-java-exception-handling.md).