version: "1.0.0" name: 181-java-observability-logging description: Use when you need to implement or improve Java logging and observability — including selecting SLF4J with Logback/Log4j2, applying proper log levels (ERROR, WARN, INFO, DEBUG, TRACE), parameterized logging, correlation context, secure logging without sensitive data exposure, environment-specific configuration, log aggregation, monitoring, and alerting. This should trigger for requests such as Improve logging; Apply logging; Refactor logging; Add logging support; Review SLF4J structured logging in Java code. Part of Plinth Toolkit license: Apache-2.0 metadata: author: Juan Antonio Breña Moral version: 0.19.0

Java Logging Best Practices

Implement effective Java logging following standardized frameworks, meaningful log levels, core practices (parameterized logging, exception handling, no sensitive data), explicit correlation context, flexible configuration, security-conscious logging, monitoring, and alerting.

What is covered in this Skill?

• Standardized framework selection: SLF4J facade with Logback or Log4j2
• Meaningful and consistent log levels: ERROR, WARN, INFO, DEBUG, TRACE
• Core practices: parameterized logging, proper exception handling, avoiding sensitive data
• Configuration: environment-specific (logback.xml, log4j2.xml), output formats, log rotation
• Security: mask sensitive data, control log access, secure transmission, GDPR/HIPAA compliance
• Log monitoring and alerting: centralized aggregation (ELK, Splunk, Loki), automated alerts

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 logging recommendations, ensure the project compiles. Compilation failure is a blocking condition. After applying improvements, run full verification.

• MANDATORY: Run ./mvnw compile or mvn compile before applying any change
• SAFETY: If compilation fails, stop immediately — do not proceed until resolved
• 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 logging pattern

When to use this skill

• Improve logging
• Apply logging
• Refactor logging
• Add logging support
• Review SLF4J structured logging in Java code

Workflow

1. Compile project before logging changes

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

1. Read logging reference and assess current observability

Read references/181-java-observability-logging.md and evaluate framework usage, log levels, sensitive-data handling, and config gaps.

1. Apply logging and observability improvements

Implement selected framework/configuration/practice changes, including secure logging and monitoring integration where applicable.

1. Verify with full build

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

Reference

For detailed guidance, examples, and constraints, see references/181-java-observability-logging.md.