Log4j2 Extensions

Spring Boot includes a number of extensions to Log4j2 that can help with advanced configuration. You can use these extensions in any log4j2-spring.xml configuration file.

Because the standard log4j2.xml configuration file is loaded too early, you cannot use extensions in it. You need to either use log4j2-spring.xml or define a logging.config property.

The extensions supersede the Spring Boot support provided by Log4J. You should make sure not to include the org.apache.logging.log4j:log4j-spring-boot module in your build.

Profile-specific Configuration

The <SpringProfile> tag lets you optionally include or exclude sections of configuration based on the active Spring profiles. Profile sections are supported anywhere within the <Configuration> element. Use the name attribute to specify which profile accepts the configuration. The <SpringProfile> tag can contain a profile name (for example staging) or a profile expression. A profile expression allows for more complicated profile logic to be expressed, for example production & (eu-central | eu-west). Check the Spring Framework reference guide for more details. The following listing shows three sample profiles:

<SpringProfile name="staging">
	<!-- configuration to be enabled when the "staging" profile is active -->
</SpringProfile>

<SpringProfile name="dev | staging">
	<!-- configuration to be enabled when the "dev" or "staging" profiles are active -->
</SpringProfile>

<SpringProfile name="!production">
	<!-- configuration to be enabled when the "production" profile is not active -->
</SpringProfile>

Environment Properties Lookup

If you want to refer to properties from your Spring Environment within your Log4j2 configuration you can use spring: prefixed lookups. Doing so can be useful if you want to access values from your application.properties file in your Log4j2 configuration.

The following example shows how to set a Log4j2 property named applicationName that reads spring.application.name from the Spring Environment:

<Properties>
	<Property name="applicationName">${spring:spring.application.name}</Property>
</Properties>

The lookup key should be specified in kebab case (such as my.property-name).

Log4j2 System Properties

Log4j2 supports a number of System Properties that can be used to configure various items. For example, the log4j2.skipJansi system property can be used to configure if the ConsoleAppender will try to use a Jansi output stream on Windows.

All system properties that are loaded after the Log4j2 initialization can be obtained from the Spring Environment. For example, you could add log4j2.skipJansi=false to your application.properties file to have the ConsoleAppender use Jansi on Windows.

The Spring Environment is only considered when system properties and OS environment variables do not contain the value being loaded.

System properties that are loaded during early Log4j2 initialization cannot reference the Spring Environment. For example, the property Log4j2 uses to allow the default Log4j2 implementation to be chosen is used before the Spring Environment is available.