Spring Boot Tutorial 0/110 lessons ~6 min read Lesson 23“Production-grade backends”

Logging Basics

Spring Boot uses SLF4J as the API and Logback as the default implementation.

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Focus

3 guided sections

Practice signal

Examples included

Career prep

Foundation builder

Introduction

Spring Boot uses SLF4J as the API and Logback as the default implementation. Log structured JSON in production, human-readable in dev — no System.out.println ever.

Informative example

@Service
@Slf4j  // Lombok – generates 'private static final Logger log = ...'
public class OrderService {
  public Order place(NewOrder cmd) {
    log.info("Placing order user={} items={}", cmd.userId(), cmd.items().size());
    try {
      ...
    } catch (Exception ex) {
      log.error("Order placement failed user={}", cmd.userId(), ex);
      throw ex;
    }
  }
}

# application.yml
logging:
  level:
    root: INFO
    com.acme: DEBUG
  pattern:
    console: "%d{ISO8601} %-5level [%thread] %logger - %msg%n"

Best practices

Log levels: TRACE → DEBUG → INFO → WARN → ERROR. Default INFO in prod.
Use parameterised messages (log.info("x={}", x)) — lazy formatting.
Add a correlation/trace ID to every request via MDC.

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