Spring Boot Logging Levels, Configuration & Starter Properties

Logging in Java and Spring Boot is a crucial mechanism for tracking the behavior of applications, debugging issues, and auditing events during runtime. It allows developers to output messages about the application’s execution process, which can be very useful for monitoring and diagnosing problems.
How Logging Works in Java
Java offers logging capabilities through several frameworks. At its core, Java includes a basic logging framework in java.util.logging, but more robust frameworks are often used in enterprise applications, such as Log4j, SLF4J, and Logback.
Logging frameworks follow a general pattern where messages are categorized into different severity levels (log levels). These messages are then sent to various outputs, such as the console or log files.
Logging in Spring Boot
Spring Boot provides extensive support for logging by using SLF4J as the API layer and Logback as the default logging implementation. It automatically configures logging based on the underlying framework, but developers have the flexibility to change this configuration and even use other logging frameworks like Log4j or Log4j2.
Log Levels in Java and Spring Boot
Logging frameworks typically support different log levels to classify messages by their importance. The standard log levels are:
TRACE: The most detailed logging level. It includes fine-grained, diagnostic information used primarily for debugging at the most granular level.
DEBUG: Similar to TRACE but with slightly less detail. It is useful for debugging and provides insight into the internal workings of an application.
INFO: Provides general, high-level information about the application’s execution. It is less detailed than DEBUG and focuses on key events or progress indicators.
WARN: Indicates that something unexpected occurred, or there is a potential issue, but the application can still run. It warns of situations that could become errors if not addressed.
ERROR: Logs serious issues that have occurred during application execution, typically preventing certain operations from completing. These messages indicate the need for immediate attention.
FATAL (sometimes not included in all frameworks): Indicates critical failures that force the application to terminate.
Log levels allow developers to control the verbosity of the logs. In production, it's common to use INFO or WARN levels, while during development, DEBUG or TRACE levels are more helpful.
How SLF4J Works
SLF4J (Simple Logging Facade for Java) is a logging abstraction that allows developers to use a consistent logging API across different logging implementations. SLF4J does not handle the actual logging itself but delegates logging calls to the underlying logging framework, such as Logback or Log4j.
This abstraction is beneficial because it decouples the application code from any specific logging implementation. If developers want to switch the logging backend from Logback to Log4j2, they can do so without changing their logging code - only the underlying logging configuration needs to be updated.
In Spring Boot, SLF4J is the default logging facade. Behind the scenes, it binds to Logback by default, but you can configure it to use other logging implementations.
Other Logging Frameworks
Spring Boot supports multiple logging frameworks, allowing developers to customize logging behavior based on their needs. Some common logging frameworks used with Spring Boot are:
Logback: The default logging implementation for Spring Boot. It’s a powerful, flexible logging framework that supports advanced features like log rolling and conditional logging.
Log4j and Log4j2: Older and newer versions of Apache's logging framework, respectively. Log4j2 is more powerful and efficient compared to Log4j and is commonly used in high-performance applications.
java.util.logging (JUL): The logging API that comes with the JDK. It’s not as feature-rich as Logback or Log4j, but it can still be used in applications, especially when lightweight logging is sufficient.
Commons Logging: A logging facade that was once more popular but is now largely replaced by SLF4J.
In Spring Boot, you can easily switch to any of these frameworks by adding the relevant dependencies to your project. Spring Boot auto-configures the logging framework based on the dependencies present, making it easy to integrate different logging frameworks without much manual configuration.

[@jibrilrichter2852]

You are a wonderful teacher!

[@cameronmcnz]

Thanks for the kind words! What topic should I cover next?

[@jibrilrichter2852]

@ Spring Security, CORS. II like the way you simplify complex concepts, thanks.

[@cameronmcnz]

@@jibrilrichter2852 Imma need someone to explain those things to me first. They confuse the life out of me!
Thanks again for the kind words. I'll put those topics on my short list.

[@TochukwuVictor-qe4xd]

Nice boss 🎉

[@RoginoSalcedo]

Very useful!! It helped me a lot, thanks

[@cameronmcnz]

Very happy to help out. Have fun working with Spring and Spring Boot!

[@scrumtuous]

Very nice. Logging in Spring Boot made easy!