Logging is one of the most critical aspects of any production-ready application.
Spring Boot provides sensible default logging out of the box while allowing deep customization when needed.

This post explains how logging works in Spring Boot, how to configure it, and how to apply best practices.

1. Why Logging Matters

Proper logging helps you:

• Debug issues quickly
• Monitor application behavior
• Investigate production failures
• Understand performance bottlenecks

Without good logging, troubleshooting becomes guesswork.

2. Default Logging in Spring Boot

Spring Boot uses Logback as the default logging framework.

Out of the box, it provides:

• Console logging
• Preconfigured log format
• Sensible log levels

You get logging without writing any configuration.

3. Logging Abstraction: SLF4J

Spring Boot uses SLF4J as a logging facade.

You should always code against SLF4J:

private static final Logger log =
        LoggerFactory.getLogger(MyService.class);

log.info("Application started");

This keeps your code independent of the underlying logging implementation.

4. Log Levels Explained

Spring Boot supports standard log levels:

5. Configuring Log Levels

You can configure logging levels in application.properties or application.yml.

logging.level.root=INFO
logging.level.org.springframework=INFO
logging.level.com.example=DEBUG

This allows fine-grained control per package.

6. Logback Configuration (Advanced)

For advanced needs, use a logback-spring.xml file.

Example:

<configuration>
    <appender name="CONSOLE"
              class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%d{yyyy-MM-dd HH:mm:ss} %-5level %logger - %msg%n</pattern>
        </encoder>
    </appender>

    <root level="INFO">
        <appender-ref ref="CONSOLE"/>
    </root>
</configuration>

Spring Boot automatically detects this file.

7. File Logging

Enable file logging easily:

logging.file.name=app.log
logging.file.path=/var/logs

This is essential for production environments.

8. Logging with Profiles

Different environments require different logging levels.

Example:

# application-dev.properties
logging.level.root=DEBUG

# application-prod.properties
logging.level.root=INFO

Profiles allow safe and clean separation.

9. Logging Exceptions Correctly

Always log exceptions properly:

try {
    process();
} catch (Exception e) {
    log.error("Processing failed", e);
}

Avoid:

• Swallowing exceptions
• Logging stack traces as strings

10. Common Logging Mistakes

• Using System.out.println
• Logging sensitive data
• Excessive DEBUG logging in production
• Logging inside tight loops

11. Best Practices

• Use SLF4J everywhere
• Choose correct log levels
• Use structured, meaningful messages
• Reduce logging in production
• Centralize logs using tools (ELK, Grafana)

12. Summary

• Spring Boot uses Logback by default
• SLF4J is the logging facade
• Logging levels control verbosity
• Configuration is simple yet powerful
• Proper logging is essential for production readiness

What's Next?

Next post:

35 - Spring Boot DevTools – Hot Reloading

We’ll explore how DevTools improves developer productivity.