Allow addition of custom logback Actions

[a1dutch]

Hi,

I was looking at adding a custom Action via the SpringBootJoranConfigurator but this is not currently possible.

My use case is to enable or disable an appender based on a property via the spring Environment class.

I managed to add a custom action based on the newRule extension, but its not possible to get access to the Environment class.

A way to either configure the SpringBootJoranConfigurator with the LoggingInitializationContext or a new way to enable/disable based on a property would be handy, e.g. like a <conditionalOnProperty property="my.property.enabled" havingValue="true" matchOnMissing=true />

Cheers

Andy

[philwebb]

I wonder if we could update SpringBootJoranConfigurator to add additional JoranConfigurator instances loaded via spring.factories.

I managed to add a custom action based on the newRule extension

@a1dutch How did you do this? Can you share some code?

[wilkinsona]

In Logback, conditional configuration is typically handled via Janino. It would be less general purpose, but for this specific use case I wonder if we should looking at making the Environment available to Janino's expressions? By default they are "a Java expression in which only context properties or system properties are accessible".

[a1dutch]

@philwebb - here is the docs for newRule: http://logback.qos.ch/manual/onJoran.html#newRule

here is my working example based on classes present, the following is added to logback-spring.xml

<newRule pattern="configuration/enabledWhenClassPresent" actionClass="****.logging.slf4j.EnabledWhenClassPresentAction"/>

<enabledWhenClassPresent class="some.classname.Here">
...
</enabledWhenClassPresent>

The EnabledWhenClassPresentAction is the same as SpringPropertyAction apart from its doing a Class.forname to check if the class exists.

i think two new actions supported by default (enabled based on a property & enabled based on class present) would be a good addition to spring boot and cover any possible use cases.

@wilkinsona i initially looked at Janino expressions, i will take another look and see if its possible to use springProperty in conjunction with this.

[philwebb]

I wonder if we can put the org.springframework.boot.logging.LoggingInitializationContext class into ch.qos.logback.core.Context? That way Actions could get it via the InterpretationContext. E.g.:

LoggingInitializationContext lic = (LoggingInitializationContext) context.getContext().getObject(LoggingInitializationContext.class.getName());

[a1dutch]

@philwebb yes that would be super handy

[michaelplavnik]

@philwebb

"to add additional JoranConfigurator"

sounds like introducing

interface JoranConfiguratorCustomizer { void addInstanceRules(RuleStore rs, SpringBootJoranConfigurator c); }

and environment property to manage a set of customizers