Reflection in Logback instrumentation breaks Android support

[bencehornak]

Describe the bug

The Logback instrumentation crashes on Android since version 2.11.0, because Android doesn't support the reflection that was introduced in #12513. In particular the crash occurs during the class initialization of LoggingEventMapper, when it refers to java.lang.ClassValue, which is absent on Android below API level 34.

opentelemetry-java-instrumentation/instrumentation/logback/logback-appender-1.0/library/src/main/java/io/opentelemetry/instrumentation/logback/appender/v1_0/internal/LoggingEventMapper.java

Lines 73 to 79 in 5b21872

	private static final ClassValue<FieldReader> valueField =
	new ClassValue<FieldReader>() {
	@Override
	protected FieldReader computeValue(Class<?> type) {
	return createFieldReader(type);
	}
	};

Steps to reproduce

Configure Logback to use the OpenTelemetryAppender on Android:

logback.xml

<configuration>
  <root>
    <appender name="opentelemetry" class="io.opentelemetry.instrumentation.logback.appender.v1_0.OpenTelemetryAppender" />
  </root>
</configuration>

And then initialize logback.

Expected behavior

The LoggingEventMapper class should carefully check for the existence of the ClassValue class (just like it does in supportsLogstashMarkers() with other classes) and it should only try to instantiate ClassValue, if it is available. Otherwise it should continue without the Logstash functionality added in #12513.

Actual behavior

The LoggingEventMapper class crashes on Android during the class initialization:

java.lang.NoClassDefFoundError: Failed resolution of: Ljava/lang/ClassValue;
	at io.opentelemetry.instrumentation.logback.appender.v1_0.internal.LoggingEventMapper.builder(LoggingEventMapper.java:105)
	at io.opentelemetry.instrumentation.logback.appender.v1_0.OpenTelemetryAppender.start(OpenTelemetryAppender.java:82)
	at ch.qos.logback.core.joran.action.AppenderAction.end(Unknown Source:13)
	at ch.qos.logback.core.joran.spi.Interpreter.callEndAction(Unknown Source:23)
	at ch.qos.logback.core.joran.spi.Interpreter.endElement(Unknown Source:34)
	at ch.qos.logback.core.joran.spi.Interpreter.endElement(Unknown Source:11)
	at ch.qos.logback.core.joran.spi.EventPlayer.play(Unknown Source:84)
	at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(Unknown Source:16)
	at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(Unknown Source:18)
	at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(Unknown Source:8)
	at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(Unknown Source:24)
	at ch.qos.logback.classic.util.ContextInitializer.autoConfig(Unknown Source:32)
    ...
Caused by: java.lang.ClassNotFoundException: Didn't find class "java.lang.ClassValue" on path: DexPathList[[...]]
	at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:196)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:312)

Javaagent or library instrumentation version

2.12.0

Environment

JDK: Android
OS: Android (API level 29)

Additional context

I will submit a bugfix in the next days, if I have some free time.