记录一个 ClassLoaderHandler 类加载问题排查

[hengyunabc]

在目前代码里，有一个 dubbo的示例，里面有一个 com.test.dubbo.DubboPluginClassLoaderHandler

public class DubboPluginClassLoaderHandler implements ClassLoaderHandler {

    @Override
    public Class<?> loadClass(String name) {
        if (name.startsWith("com.test.dubbo")) {
            try {
                Class<?> clazz = this.getClass().getClassLoader().loadClass(name);
                return clazz;
            } catch (Throwable e) {
                e.printStackTrace();
            }
        }
        return null;
    }

}

显然它是为了保证 dubbo-test-plugin-common 下的测试类 com.test.dubbo.RpcUtils 能被其它ClassLoader正常加载。

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当用户自己写了一个 dubbo 的测试，里面的代码是 com.test.dubbo.EchoService ，这里就出现问题了。

• package 和 DubboPluginClassLoaderHandler 里的重名了，导致应用的 com.test.dubbo.EchoService 会被 dubbo-plugin PluginClassLoader 加载。

• PluginClassLoader 目前的加载顺序，最终会向上调用 super 去查找，PluginClassLoader 的 parent 是启动 one-java-agent 的 ClassLoader 。

• 所以最终可能 com.test.dubbo.EchoService 是被 one-java-agent 的 ClassLoader 加载到。而并不是应用的 ClassLoader。

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一个异常栈：

Thread [main] (Suspended (breakpoint at line 26 in AgentSpyImpl))	
	owns: Object  (id=11559)	
	owns: OneAgentClassLoader  (id=11560)	
	owns: PluginClassLoader  (id=11561)	
	owns: Object  (id=11562)	
	AgentSpyImpl.loadClass(String) line: 26	
	Launcher$AppClassLoader(ClassLoader).loadClass(String) line: 49	
	ClassLoader.defineClass1(String, byte[], int, int, ProtectionDomain, String) line: not available [native method]	
	Launcher$AppClassLoader(ClassLoader).defineClass(String, byte[], int, int, ProtectionDomain) line: 763	
	Launcher$AppClassLoader(SecureClassLoader).defineClass(String, byte[], int, int, CodeSource) line: 142	
	Launcher$AppClassLoader(URLClassLoader).defineClass(String, Resource) line: 468	
	URLClassLoader.access$100(URLClassLoader, String, Resource) line: 74	
	URLClassLoader$1.run() line: 369	
	URLClassLoader$1.run() line: 363	
	AccessController.doPrivileged(PrivilegedExceptionAction<T>, AccessControlContext) line: not available [native method]	
	Launcher$AppClassLoader(URLClassLoader).findClass(String) line: 362	
	Launcher$AppClassLoader(ClassLoader).loadClass(String, boolean) line: 424	
	Launcher$AppClassLoader.loadClass(String, boolean) line: 349	
	OneAgentClassLoader(ClassLoader).loadClass(String, boolean) line: 411	
	PluginClassLoader(ClassLoader).loadClass(String, boolean) line: 411	
	PluginClassLoader.loadClass(String, boolean) line: 144	
	PluginClassLoader(ClassLoader).loadClass(String) line: 357	
	DubboPluginClassLoaderHandler.loadClass(String) line: 16	
	ClassLoaderHandlerManagerImpl.loadClass(String) line: 80	
	AgentSpyImpl.loadClass(String) line: 26	
	ReLaunchURLClassLoader(ClassLoader).loadClass(String) line: 49	
	Class<T>.forName0(String, boolean, ClassLoader, Class<?>) line: not available [native method]	
	Class<T>.forName(String, boolean, ClassLoader) line: 348	
	ClassUtils.forName(String, ClassLoader) line: 280	
	ClassUtils.resolveClassName(String, ClassLoader) line: 320	
	ServiceClassPostProcessor.resolveClass(BeanDefinition) line: 361	
	ServiceClassPostProcessor.resolveClass(BeanDefinitionHolder) line: 353	
	ServiceClassPostProcessor.registerServiceBean(BeanDefinitionHolder, BeanDefinitionRegistry, DubboClassPathBeanDefinitionScanner) line: 279	
	ServiceClassPostProcessor.registerServiceBeans(Set<String>, BeanDefinitionRegistry) line: 175	
	ServiceClassPostProcessor.postProcessBeanDefinitionRegistry(BeanDefinitionRegistry) line: 134	
	PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(Collection<BeanDefinitionRegistryPostProcessor>, BeanDefinitionRegistry) line: 275	
	PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory, List<BeanFactoryPostProcessor>) line: 125	
	AnnotationConfigApplicationContext(AbstractApplicationContext).invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory) line: 706	
	AnnotationConfigApplicationContext(AbstractApplicationContext).refresh() line: 532	
	SpringApplication.refresh(ApplicationContext) line: 744	
	SpringApplication.refreshContext(ConfigurableApplicationContext) line: 391	
	SpringApplication.run(String...) line: 312	
	SpringApplication.run(Class<?>[], String[]) line: 1215	
	SpringApplication.run(Class<?>, String...) line: 1204	
	Application.main(String[]) line: 33	
	NativeMethodAccessorImpl.invoke0(Method, Object, Object[]) line: not available [native method]	
	NativeMethodAccessorImpl.invoke(Object, Object[]) line: 62	
	DelegatingMethodAccessorImpl.invoke(Object, Object[]) line: 43	
	Method.invoke(Object, Object...) line: 498	
	LaunchRunner.run() line: 38	
	Thread.run() line: 748	

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TODO

• 仔细定义启动 one-java-agent的 ClassLoader 和 PluginClassLoader 的行为
• 使用 ClassLoaderHandler 时要非常小心