Logging is essential in any Spring Boot application. It helps you track what your application is doing, troubleshoot problems, and monitor how your code behaves in real time. When your application runs, logs provide a record of key events, errors, and information that can help you quickly find and fix issues. In this chapter, you will learn about the logging frameworks available in Spring Boot and how you can use them to make your applications easier to understand and maintain.

Logging Frameworks

Spring Boot supports several popular logging frameworks to help you record and manage application events. The main frameworks are Logback, Log4j2, and SLF4J. Each one serves a specific role in how you capture and format log messages in your application.

Logback is the default logging framework in Spring Boot. It is fast, flexible, and easy to configure. You use Logback to control how logs are written, their format, and where they are stored. By default, Spring Boot writes logs to the console, but you can easily send logs to files or other destinations by updating the application.properties file.

Log4j2 is another powerful logging framework supported by Spring Boot. It offers advanced features like asynchronous logging, custom layouts, and filtering. To use Log4j2, you need to add the appropriate dependency and exclude Logback. Log4j2 is useful when you need more control over performance or log formatting in complex applications.

SLF4J acts as a simple logging facade. It does not write logs itself but provides a common API that lets you switch between different logging frameworks like Logback or Log4j2 without changing your code. In Spring Boot, you typically write log statements using the Logger interface from SLF4J. This approach keeps your code flexible and framework-independent.

In a typical Spring Boot project, you can start logging messages by injecting an SLF4J Logger and calling methods like info(), debug(), or error(). The actual logging framework used under the hood depends on your project dependencies and configuration.