import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class UserService {
    private static final Logger log = LoggerFactory.getLogger(UserService.class);

    // Or with Lombok
    // @Slf4j on class
}

log.trace("Detailed debug info: {}", details);
log.debug("Debug info for development");
log.info("Normal operation: user {} logged in", userId);
log.warn("Potential problem: {} retries remaining", retries);
log.error("Error occurred: {}", message, exception);

// Good - lazy evaluation
log.debug("Processing order {} for user {}", orderId, userId);

// Avoid - always evaluates
log.debug("Processing order " + orderId + " for user " + userId);

// Multiple parameters
log.info("User {} performed {} on resource {}", userId, action, resourceId);

try {
    processOrder(order);
} catch (OrderException e) {
    // Exception is always last parameter
    log.error("Failed to process order {}: {}", order.getId(), e.getMessage(), e);
}

import org.slf4j.MDC;

// Set context
MDC.put("requestId", requestId);
MDC.put("userId", userId);

try {
    // All logs in this scope will include requestId and userId
    log.info("Processing request");
} finally {
    MDC.clear();
}

if (log.isDebugEnabled()) {
    log.debug("Expensive computation result: {}", expensiveMethod());
}

// Better with lambdas (SLF4J 2.0+)
log.atDebug().log(() -> "Result: " + expensiveMethod());

log.atInfo()
   .addKeyValue("orderId", orderId)
   .addKeyValue("amount", amount)
   .log("Order processed successfully");