How do you create a custom logging configuration in Spring Boot?

Table of Contents

• Introduction
• Steps to Create a Custom Logging Configuration in Spring Boot
  • 1. Understand Default Logging in Spring Boot
  • 2. Using **application.properties** or **application.yml** for Basic Configuration
    • Example using application.properties:
    • Example using application.yml:
  • 3. Creating a Custom Logback Configuration File
    • Example logback-spring.xml:
  • 4. Configuring Log Levels Programmatically
  • 5. Customizing Log Output Format
    • Example:
  • 6. Rolling File Appender Configuration
    • Example:
• Conclusion

Introduction

Logging is a crucial part of any Spring Boot application, helping to monitor application behavior, debug issues, and track performance. By default, Spring Boot uses a logging framework called Spring Boot Logging which integrates Logback as the default logging implementation. However, you might want to customize the logging configuration to meet specific needs, such as altering log levels, changing log output format, or routing logs to different destinations.

In this guide, we will explore how to create a custom logging configuration in Spring Boot, covering basic setup, log formatting, log levels, and custom output destinations.

Steps to Create a Custom Logging Configuration in Spring Boot

1. Understand Default Logging in Spring Boot

Spring Boot uses Logback by default for logging. It supports various configurations, such as:

• Log Levels: Debug, Info, Warn, Error, etc.
• Log Patterns: Format log output with patterns like timestamp, log level, class name, and message.
• Log Destinations: Direct logs to different outputs (console, file, or external systems).

In Spring Boot, logging is automatically configured with sensible defaults, but you can override these defaults using a custom configuration.

2. Using **application.properties** or **application.yml** for Basic Configuration

You can configure logging at a high level using properties in **application.properties** or **application.yml**.

Example using application.properties:

Example using application.yml:

Explanation:

• **logging.level.root**: Sets the default log level (INFO) for the entire application.
• **logging.level.org.springframework.web**: Sets a DEBUG level for Spring Web package logs.
• **logging.level.com.myapp**: Sets TRACE level for logs in your application package.
• **logging.pattern.console**: Configures the log format for the console.
• **logging.file.name**: Specifies the location of the log file.

These settings are often enough for basic logging customizations.

3. Creating a Custom Logback Configuration File

For more advanced logging configurations, you can create a custom **logback-spring.xml** file. This file gives you complete control over loggers, appenders, and patterns.

Example logback-spring.xml:

Explanation:

• **<appender>**: Specifies the destination for logs (e.g., console or file).
• **<encoder>**: Defines the log output format (you can use %d for timestamp, %msg for the log message, etc.).
• **<root>**: Configures the root logger with a specified log level (e.g., INFO) and attaches the appenders.
• **<logger>**: Allows setting a custom log level for specific packages or classes.

You can put this logback-spring.xml file in your **src/main/resources** directory, and Spring Boot will automatically use it.

4. Configuring Log Levels Programmatically

If you want to change log levels dynamically during application runtime, you can do this programmatically using the Logger class from SLF4J (which Spring Boot uses).

For example, to change the log level for a specific package dynamically:

In this example, the log level of the **com.myapp** package is dynamically changed to DEBUG.

5. Customizing Log Output Format

Customizing the format of your log output can help you track important information, such as application version, hostname, or thread ID. This is typically done in the encoder configuration within logback-spring.xml.

Example:

This pattern produces output like:

6. Rolling File Appender Configuration

In production applications, you might want to rotate logs to avoid creating large log files. You can configure rolling log files using the RollingFileAppender in logback-spring.xml.

Example:

This configuration rolls the log file when it reaches a certain size or when the maximum number of logs is reached (in this case, 5).

Conclusion

Creating a custom logging configuration in Spring Boot allows you to have more control over how logs are handled, formatted, and stored. By leveraging application.properties/application.yml for simple configurations or logback-spring.xml for more advanced setups, you can ensure that your application logs provide meaningful insights while maintaining flexibility for different environments. Whether you're dealing with log levels, file rotations, or custom formats, Spring Boot makes it easy to adapt logging to your needs.