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

Compile project before logging changes

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

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.

Apply logging and observability improvements

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

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.