Structured Logging

Spring Boot 3.4+ supports structured logging natively: set logging.structured.format.console to ecs, gelf or logstash to emit JSON with trace IDs and MDC values. Use SLF4J parameterized logging, add context with MDC (request ID, tenant), log at appropriate levels, and never log secrets or full request bodies.

@Component
class TenantMdcFilter extends OncePerRequestFilter {
    @Override
    protected void doFilterInternal(HttpServletRequest req, HttpServletResponse res, FilterChain chain)
            throws ServletException, IOException {
        try {
            MDC.put("tenant", req.getHeader("X-Tenant-Id"));
            chain.doFilter(req, res);
        } finally {
            MDC.remove("tenant");
        }
    }
}

@Service
class OrderService {
    private static final Logger log = LoggerFactory.getLogger(OrderService.class);

    void cancel(long orderId, String reason) {
        log.info("Order cancelled orderId={} reason={}", orderId, reason);   // parameterized
    }
}

logging:
  structured:
    format:
      console: ecs
  level:
    com.example.shop: INFO

Common pitfalls

• String concatenation in log calls (wasted work when level is disabled).
• Not clearing MDC in thread pools (context leaks to other requests).
• Logging tokens, passwords or full payloads.

Key points

• Native JSON logging (ECS/GELF/Logstash)
• MDC for request context; always clear it
• Parameterized messages, no secrets

Further reading: Spring Boot: Structured logging