Support Janino in a native image

[gdrouet]

When building a native image with Spring Boot Maven plugin, Logback configuration relying on Janino leads to an error.

For instance, if we add to the logback-spring.xml file the following if statement:

        <if condition='isDefined("ENV")'>
            <then>
                <appender-ref ref="CONSOLE_JSON"/>
            </then>
            <else>
                <appender-ref ref="CONSOLE_LOCAL"/>
            </else>
        </if>

Then running a native image lead to this error:

Logging system failed to initialize using configuration from 'null'
java.util.EmptyStackException
	at java.base@17.0.5/java.util.Stack.peek(Stack.java:101)
	at ch.qos.logback.core.model.processor.ModelInterpretationContext.peekModel(ModelInterpretationContext.java:84)
	at ch.qos.logback.core.model.processor.conditional.ElseModelHandler.handle(ElseModelHandler.java:45)
	at ch.qos.logback.core.model.processor.DefaultProcessor.secondPhaseTraverse(DefaultProcessor.java:241)
	at ch.qos.logback.core.model.processor.DefaultProcessor.secondPhaseTraverse(DefaultProcessor.java:253)
	at ch.qos.logback.core.model.processor.DefaultProcessor.secondPhaseTraverse(DefaultProcessor.java:253)
	at ch.qos.logback.core.model.processor.DefaultProcessor.secondPhaseTraverse(DefaultProcessor.java:253)
	at ch.qos.logback.core.model.processor.DefaultProcessor.traversalLoop(DefaultProcessor.java:90)
	at ch.qos.logback.core.model.processor.DefaultProcessor.process(DefaultProcessor.java:106)
	at ch.qos.logback.core.joran.GenericXMLConfigurator.processModel(GenericXMLConfigurator.java:200)
	at org.springframework.boot.logging.logback.SpringBootJoranConfigurator.processModel(SpringBootJoranConfigurator.java:122)
	at org.springframework.boot.logging.logback.SpringBootJoranConfigurator.configureUsingAotGeneratedArtifacts(SpringBootJoranConfigurator.java:115)
	at org.springframework.boot.logging.logback.LogbackLoggingSystem.initializeFromAotGeneratedArtifactsIfPossible(LogbackLoggingSystem.java:210)
	at org.springframework.boot.logging.logback.LogbackLoggingSystem.initialize(LogbackLoggingSystem.java:187)
	at org.springframework.boot.context.logging.LoggingApplicationListener.initializeSystem(LoggingApplicationListener.java:332)
	at org.springframework.boot.context.logging.LoggingApplicationListener.initialize(LoggingApplicationListener.java:298)
	at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationEnvironmentPreparedEvent(LoggingApplicationListener.java:246)
	at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationEvent(LoggingApplicationListener.java:223)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:176)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:169)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:143)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:131)
	at org.springframework.boot.context.event.EventPublishingRunListener.multicastInitialEvent(EventPublishingRunListener.java:136)
	at org.springframework.boot.context.event.EventPublishingRunListener.environmentPrepared(EventPublishingRunListener.java:81)
	at org.springframework.boot.SpringApplicationRunListeners.lambda$environmentPrepared$2(SpringApplicationRunListeners.java:64)
	at java.base@17.0.5/java.lang.Iterable.forEach(Iterable.java:75)
	at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:118)
	at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:112)
	at org.springframework.boot.SpringApplicationRunListeners.environmentPrepared(SpringApplicationRunListeners.java:63)
	at org.springframework.boot.SpringApplication.prepareEnvironment(SpringApplication.java:352)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:303)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1302)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1291)

Note that a fat-jar run with -Dspring.aot.enabled=true does not help to reproduce the issue.

It would be great to have such support for native image.

[wilkinsona]

https://stackoverflow.com/questions/75514151/spring-boot-native-image-does-not-print-logs-when-logback-is-configured-with-con contains another sample that exhibits slightly different faulty behaviour – this sample starts successfully but no logging output is produced.

[hpoettker]

In the example from the stackoverflow question, I also get the exception from the original post if no metadata is added to src/main/resources/META-INF/native-image.

[wilkinsona]

Unfortunately, supporting Janino is non-trivial. It relies on generating ch.qos.logback.core.joran.conditional.Condition implementations at runtime, something that Graal does not support. Spring Native hacked around this with a substitution. This option is not open to us. We do not use substitutions in Boot as the Graal team have been clear that they should not be used.

One option that we could explore is generating the Condition implementations at build time, including them in the native image and then reusing these pre-generated classes at runtime. This is what Framework does for CGLib-based proxies. This may not be possible without changes to Logback if the necessary hook points are not available.

[wilkinsona]

I've prototyped something in this branch. It's not a lot of code, but I'm not happy with AotIfModelHandler. It duplicates much of the logic in Logback's IfModelHandler which would be at risk of falling out of sync. I'd like to discuss our options with the rest of the team. My feeling is that we won't be able to do something here without some changes to Logback.

[hpoettker]

@wilkinsona Thanks for implementing #34315 so quickly! The sample application from the stackoverflow question now fails early and logs a meaningful exception. I've added it to the SO question.

[gdrouet]

Do you have any workaround to write an equivalent programmatically and have a chance to make it work with spring native?

[wilkinsona]

I'm afraid not. #25847 is tracking support for programmatic configuration of Logback.