java-logging-patterns

In Spring Boot 3.4+, set logging.structured.format.console to logstash in application.yml with no extra dependencies. For older versions, add the logstash-logback-encoder dependency and configure a LogstashEncoder appender in logback-spring.xml.

Create a servlet filter that puts a requestId into MDC at the start of each request and clears it in a finally block. Every subsequent log entry automatically includes the requestId, letting you filter all logs for one request.

Yes, Spring Boot 3.4 added native structured logging supporting logstash, ecs, and gelf formats through configuration only. Earlier versions require the logstash-logback-encoder library to produce JSON output.

MDC is thread-local, so it does not propagate to new threads automatically. Copy the context with MDC.getCopyOfContextMap() before submitting the async task, then call MDC.setContextMap() inside the new thread and clear it afterward.

Never log passwords, full card numbers, authentication tokens, or PII such as social security numbers. Log safe alternatives instead, like userId, the last four card digits, or token subject and expiry claims.