OpenJDK11与Spring Cloud Finchley的不兼容问题与解决

本文的环境：OpenJDK 11.0.4，Spring Cloud finchley SR4，Spring Boot 2.0.3

最近遇到了一个问题，在feign调用的时候，时常会出现这样一个奇怪的错误：

2019-10-07 08:00:00.620 ERROR [xxx,e1ba4c7540954aa3,871b99c4576d42e3] [24] [XNIO-2 task-286][xxx:83]: URI:[/xxx], method:[PUT], 500Exception: class com.netflix.hystrix.exception.HystrixRuntimeException, xxxxx#xxxx(xxx) failed and no fallback available.

com.netflix.hystrix.exception.HystrixRuntimeException: xxxxx#xxxx(xxx)  failed and no fallback available.
        at com.netflix.hystrix.AbstractCommand$22.call(AbstractCommand.java:822) ~[hystrix-core-1.5.18.jar!/:1.5.18]
        at com.netflix.hystrix.AbstractCommand$22.call(AbstractCommand.java:807) ~[hystrix-core-1.5.18.jar!/:1.5.18]
        at rx.internal.operators.OperatorOnErrorResumeNextViaFunction$4.onError(OperatorOnErrorResumeNextViaFunction.java:140) ~[rxjava-1.3.8.jar!/:1.3.8]
省略无用堆栈
Caused by: org.springframework.beans.factory.BeanDefinitionStoreException: Failed to process import candidates for configuration class [org.springframework.cloud.netflix.ribbon.RibbonClientConfiguration]; nested exception is java.io.FileNotFoundException: class path resource [org/springframework/boot/context/properties/EnableConfigurationPropertiesImportSelector$ConfigurationPropertiesBeanRegistrar.class] cannot be opened because it does not exist
        at org.springframework.context.annotation.ConfigurationClassParser.processImports(ConfigurationClassParser.java:646) ~[spring-context-5.0.13.RELEASE.jar!/:5.0.13.RELEASE]
        at org.springframework.context.annotation.ConfigurationClassParser.doProcessConfigurationClass(ConfigurationClassParser.java:303) ~[spring-context-5.0.13.RELEASE.jar!/:5.0.13.RELEASE]
        at org.springframework.context.annotation.ConfigurationClassParser.processConfigurationClass(ConfigurationClassParser.java:245) ~[spring-context-5.0.13.RELEASE.jar!/:5.0.13.RELEASE]
        at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:202) ~[spring-context-5.0.13.RELEASE.jar!/:5.0.13.RELEASE]
        at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:170) ~[spring-context-5.0.13.RELEASE.jar!/:5.0.13.RELEASE]
        at org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(ConfigurationClassPostProcessor.java:316) ~[spring-context-5.0.13.RELEASE.jar!/:5.0.13.RELEASE]
        at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(ConfigurationClassPostProcessor.java:233) ~[spring-context-5.0.13.RELEASE.jar!/:5.0.13.RELEASE]
        at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:271) ~[spring-context-5.0.13.RELEASE.jar!/:5.0.13.RELEASE]
        at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:91) ~[spring-context-5.0.13.RELEASE.jar!/:5.0.13.RELEASE]
        at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:706) ~[spring-context-5.0.13.RELEASE.jar!/:5.0.13.RELEASE]
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:533) ~[spring-context-5.0.13.RELEASE.jar!/:5.0.13.RELEASE]
        at org.springframework.cloud.context.named.NamedContextFactory.createContext(NamedContextFactory.java:117) ~[spring-cloud-context-2.0.3.RELEASE.jar!/:2.0.3.RELEASE]
        at org.springframework.cloud.context.named.NamedContextFactory.getContext(NamedContextFactory.java:85) ~[spring-cloud-context-2.0.3.RELEASE.jar!/:2.0.3.RELEASE]
        at org.springframework.cloud.netflix.ribbon.SpringClientFactory.getContext(SpringClientFactory.java:118) ~[spring-cloud-netflix-ribbon-2.0.3.RELEASE.jar!/:2.0.3.RELEASE]
        at org.springframework.cloud.context.named.NamedContextFactory.getInstance(NamedContextFactory.java:126) ~[spring-cloud-context-2.0.3.RELEASE.jar!/:2.0.3.RELEASE]
        at org.springframework.cloud.netflix.ribbon.SpringClientFactory.getInstance(SpringClientFactory.java:108) ~[spring-cloud-netflix-ribbon-2.0.3.RELEASE.jar!/:2.0.3.RELEASE]

这个错误很奇怪，只要重新编译发布，就不会再出现。这个很有可能是打包问题，还有类加载问题。

查询github上，社区的人说是类加载问题（https://github.com/spring-cloud/spring-cloud-netflix/issues/3101#issuecomment-463382093），首先对于OpenJDK，曾经有一个Bug(https://bugs.openjdk.java.net/browse/JDK-8172726)：对于ParallelStream，我们知道默认是由JDK启动时默认启动的大小为CPU核数减1的CommonForkJoinPool执行。在多线程多类加载器环境下，这个CommonForkJoinPool可能会有Bug，就是调用Thread.contextClassLoader的时候，返回的是第一个使用CommonForkJoinPool的代码的Classloader，而不是系统根ClassLoader，这样会导致类找不到。

社区修复了这个Bug，只不过是在下一个大版本，也就是GreenWich上，对于Finchley，并没有修复。

我们考虑两种解决方案：

升级到GreenWich，这个改动很大，从Finchley到GreenWich，Bean初始化机制，JDBC连接池，等等都有了很多变化，短期内耗时费力。
参考：https://github.com/spring-cloud/spring-cloud-commons/commit/b38ce54410af8fc62d8ae6fe694b580e509ae73a#diff-8c70f107deac71db815f81fa81d5f947，覆盖源码，修改org.springframework.cloud.context.named.NamedContextFactory:

protected AnnotationConfigApplicationContext createContext(String name) { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(); if (this.configurations.containsKey(name)) { for (Class configuration : this.configurations.get(name) .getConfiguration()) { context.register(configuration); } } for (Map.Entry entry : this.configurations.entrySet()) { if (entry.getKey().startsWith("default.")) { for (Class configuration : entry.getValue().getConfiguration()) { context.register(configuration); } } } context.register(PropertyPlaceholderAutoConfiguration.class, this.defaultConfigType); context.getEnvironment().getPropertySources().addFirst(new MapPropertySource( this.propertySourceName, Collections.<String, Object> singletonMap(this.propertyName, name))); if (this.parent != null) { // Uses Environment from parent as well as beans context.setParent(this.parent); //在这里添加代码，使用parent的类加载器 context.setClassLoader(this.parent.getClassLoader()); } context.setDisplayName(generateDisplayName(name)); context.refresh(); return context; }

这样也是一种应急方案，短期内解决问题。留足时间升级。

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