Update LogAdapter to allow build-time code removal

[sdeleuze]

Allow for example to remove those classes and 90 related methods when Logback is used:

• org.apache.commons.logging.LogAdapter$JavaUtilAdapter
• org.apache.commons.logging.LogAdapter$JavaUtilLog
• org.apache.commons.logging.LogAdapter$LocationResolvingLogRecord
• org.apache.commons.logging.LogAdapter$Log4jAdapter
• org.apache.commons.logging.LogAdapter$Log4jLog
• org.apache.commons.logging.LogAdapter$LogApi
• org.apache.logging.log4j.message.ObjectMessage
• org.apache.logging.log4j.message.ReusableObjectMessage org.apache.logging.log4j.simple.SimpleLoggerContext
• org.apache.logging.log4j.simple.SimpleLoggerContextFactory

org.apache.logging.slf4j.SLF4JProvider extends org.apache.logging.log4j.spi.Provider, so a bunch of Log4j classes are still reachable, but looks like a useful improvement.

[jhoeller]

Looks good to me, also the use of Function there instead of the enum-based delegation arrangement.

[bclozel]

This change has broken the Spring Boot build. The error is currently hard to reproduce locally, but the stacktrace is:

java -jar spring-boot-smoke-test-ant.jar 
Exception in thread "main" java.lang.reflect.InvocationTargetException
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at org.springframework.boot.loader.MainMethodRunner.run(MainMethodRunner.java:49)
	at org.springframework.boot.loader.Launcher.launch(Launcher.java:95)
	at org.springframework.boot.loader.Launcher.launch(Launcher.java:58)
	at org.springframework.boot.loader.JarLauncher.main(JarLauncher.java:65)
Caused by: java.lang.NoClassDefFoundError: org/apache/logging/log4j/spi/Provider
	at java.base/java.lang.ClassLoader.defineClass1(Native Method)
	at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1012)
	at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)
	at java.base/java.net.URLClassLoader.defineClass(URLClassLoader.java:524)
	at java.base/java.net.URLClassLoader$1.run(URLClassLoader.java:427)
	at java.base/java.net.URLClassLoader$1.run(URLClassLoader.java:421)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:712)
	at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:420)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:587)
	at org.springframework.boot.loader.LaunchedURLClassLoader.loadClass(LaunchedURLClassLoader.java:149)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
	at java.base/java.lang.Class.forName0(Native Method)
	at java.base/java.lang.Class.forName(Class.java:467)
	at org.apache.commons.logging.LogAdapter.isPresent(LogAdapter.java:100)
	at org.apache.commons.logging.LogAdapter.<clinit>(LogAdapter.java:43)
	at org.apache.commons.logging.LogFactory.getLog(LogFactory.java:67)
	at org.apache.commons.logging.LogFactory.getLog(LogFactory.java:59)
	at org.springframework.boot.SpringApplication.<clinit>(SpringApplication.java:183)
	at smoketest.ant.SampleAntApplication.main(Unknown Source)
	... 8 more
Caused by: java.lang.ClassNotFoundException: org.apache.logging.log4j.spi.Provider
	at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:445)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:587)
	at org.springframework.boot.loader.LaunchedURLClassLoader.loadClass(LaunchedURLClassLoader.java:149)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
	... 27 more

[wilkinsona]

I think it's NoClassDefFoundError that needs to be caught in addition to the existing catch of ClassNotFoundException.

[sdeleuze]

I think this is now fixed, sorry for the regression, this one was pretty hard to anticipate. I think previously this potential bug was possible but hidden by the fact the classpath checks were done lazily in the static block. Thanks for catching this with Boot tests.