@Slf4j Logging

@Slf4j generates a configured SLF4J Logger as a private static final field named log, so you can start logging without the repetitive LoggerFactory.getLogger(...) declaration. SLF4J is the logging facade that Spring Boot uses by default (over Logback), making @Slf4j the natural choice for Spring applications.

The generated log field

Adding @Slf4j to a class gives you an immediately usable log reference:

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Service;

@Slf4j
@Service
public class PaymentService {

    public void charge(String orderId) {
        log.info("Charging order {}", orderId);
    }
}

Lombok generates exactly the field you would otherwise write by hand:

private static final org.slf4j.Logger log =
        org.slf4j.LoggerFactory.getLogger(PaymentService.class);

Because it is static final and keyed to the class, it follows the standard logging convention and is correctly named in your log output.

Parameterized logging

Always use SLF4J’s {} placeholders instead of string concatenation. The arguments are only converted to strings if the log level is actually enabled, which avoids wasted work in hot paths.

@Slf4j
@Service
public class OrderService {

    public Order place(OrderRequest request) {
        log.debug("Placing order for customer={} items={}",
                request.getCustomerId(), request.getItemCount());

        try {
            return process(request);
        } catch (PaymentException ex) {
            // pass the exception as the LAST argument to log the stack trace
            log.error("Payment failed for customer={}", request.getCustomerId(), ex);
            throw ex;
        }
    }
}

Tip: Do not write log.debug("order " + request) — the concatenation runs even when debug is disabled. The {} form defers it. To log an exception’s stack trace, pass the Throwable as the final argument (no placeholder for it).

Output:

2026-06-13T10:42:11.220+05:30  INFO 5120 --- [nio-8080-exec-1] c.e.app.OrderService : Placing order for customer=42 items=3
2026-06-13T10:42:11.880+05:30 ERROR 5120 --- [nio-8080-exec-1] c.e.app.OrderService : Payment failed for customer=42
com.example.app.PaymentException: card declined
    at com.example.app.OrderService.process(OrderService.java:51)
    ...

Log levels

The log field exposes the five standard SLF4J levels. Guard truly expensive message construction with an isXxxEnabled() check.

Method	Use for
log.error(...)	failures that need attention
log.warn(...)	recoverable problems, deprecations
log.info(...)	high-level lifecycle / business events
log.debug(...)	diagnostic detail for development
log.trace(...)	very fine-grained tracing

if (log.isDebugEnabled()) {
    log.debug("Computed report: {}", expensiveToString());
}

Configure thresholds per package in application.yml — see Logging Configuration:

logging:
  level:
    root: INFO
    com.example.app: DEBUG

Other logger annotations

Lombok offers one annotation per logging framework. They all generate the same log field but bind to a different backend; choose based on the facade/implementation on your classpath. With Spring Boot, @Slf4j is almost always the right one.

Annotation	Backing API
@Slf4j	SLF4J (recommended for Spring Boot)
@CommonsLog	Apache Commons Logging
@Log4j2	Apache Log4j 2
@Log	java.util.logging
@Flogger	Google Flogger

You can also rename the field with @Slf4j(topic = "audit") to log under a specific category:

@Slf4j(topic = "AUDIT")
@Component
public class AuditLogger {
    public void record(String action) {
        log.info("action={}", action); // logger named "AUDIT"
    }
}

Note: @Slf4j only declares the logger; it does not configure output format or appenders. Those are controlled by Logback (logback-spring.xml) or properties, covered in Logging Configuration.

Related Topics

• Logging Configuration
• Exception Handling Introduction
• @Data
• Introduction to Lombok
• Lombok Best Practices