[FAQ] How to make SkyWalking Java agent works in OSGI environment?

[wu-sheng]

How to make SkyWalking agent works in OSGI environment?

OSGI implements its own set of modularity, which means that each Bundle has its own unique class loader for isolating different versions of classes.
By default, OSGI runtime uses the boot classloader for the bundle codes, which makes the java.lang.NoClassDefFoundError exception in the booting stage.

java.lang.NoClassDefFoundError: org/apache/skywalking/apm/agent/core/plugin/interceptor/enhance/EnhancedInstance
	at ch.qos.logback.classic.Logger.buildLoggingEventAndAppend(Logger.java:419)
	at ch.qos.logback.classic.Logger.filterAndLog_0_Or3Plus(Logger.java:383)
	at ch.qos.logback.classic.Logger.log(Logger.java:765)
	at org.apache.commons.logging.impl.SLF4JLocationAwareLog.error(SLF4JLocationAwareLog.java:216)
	at org.springframework.boot.SpringApplication.reportFailure(SpringApplication.java:771)
	at org.springframework.boot.SpringApplication.handleRunFailure(SpringApplication.java:748)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:314)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1118)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1107)
	at by.kolodyuk.osgi.springboot.SpringBootBundleActivator.start(SpringBootBundleActivator.java:21)
	at org.apache.felix.framework.util.SecureAction.startActivator(SecureAction.java:849)
	at org.apache.felix.framework.Felix.activateBundle(Felix.java:2429)
	at org.apache.felix.framework.Felix.startBundle(Felix.java:2335)
	at org.apache.felix.framework.Felix.setActiveStartLevel(Felix.java:1566)
	at org.apache.felix.framework.FrameworkStartLevelImpl.run(FrameworkStartLevelImpl.java:297)
	at java.base/java.lang.Thread.run(Thread.java:829)

How to resolve this issue?

1. we need to set the parent classloader in OSGI to AppClassLoader, through the specific parameter org.osgi.framework.bundle.parent=app.
   The list of parameters can be found in the OSGI API
2. Load the SkyWalking related classes to the bundle parent class loader, AppClassLoader, with the parameter org.osgi.framework.bootdelegation=org.apache.skywalking.apm.*
   or org.osgi.framework.bootdelegation=*. This step is optional. Some OSGi implementations (i.e. Equinox) enable them by default

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Source from https://skywalking.apache.org/docs/skywalking-java/next/en/faq/osgi/