Logback Extensions

Spring Boot includes a number of extensions to Logback that can help with advanced configuration. You can use these extensions in your logback-spring.xml configuration file.

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

The extensions cannot be used with Logback’s configuration scanning. If you attempt to do so, making changes to the configuration file results in an error similar to one of the following being logged:

ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProperty], current ElementPath is [[configuration][springProperty]]
ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProfile], current ElementPath is [[configuration][springProfile]]

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

The <springProperty> tag lets you expose properties from the Spring Environment for use within Logback. Doing so can be useful if you want to access values from your application.properties file in your Logback configuration. The tag works in a similar way to Logback’s standard <property> tag. However, rather than specifying a direct value, you specify the source of the property (from the Environment). If you need to store the property somewhere other than in local scope, you can use the scope attribute. If you need a fallback value (in case the property is not set in the Environment), you can use the defaultValue attribute. The following example shows how to expose properties for use within Logback:

<springProperty scope="context" name="fluentHost" source="myapp.fluentd.host"
		defaultValue="localhost"/>
<appender name="FLUENT" class="ch.qos.logback.more.appenders.DataFluentAppender">
	<remoteHost>${fluentHost}</remoteHost>
	...
</appender>

The source must be specified in kebab case (such as my.property-name). However, properties can be added to the Environment by using the relaxed rules.