OpenJDK11與Spring Cloud Finchley的不兼容問題與解決

本文的環境：OpenJDK 11.0.4，Spring Cloud finchley SR4，Spring Boot 2.0.3

最近遇到了一個問題，在feign調用的時候，時常會出現這樣一個奇怪的錯誤：

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$4.onError(OperatorOnErrorResumeNextViaFunction.java:140) ~[rxjava-1.3.8.jar!/:1.3.8]
省略無用堆棧
Caused by: org.springframework.beans.factory.BeanDefinitionStoreException: Failed to process import candidates for configuration class [org.springframework.cloud.netflix.ribbon.RibbonClientConfiguration]; nested exception is java.io.FileNotFoundException: class path resource [org/springframework/boot/context/properties/EnableConfigurationPropertiesImportSelector$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]

這個錯誤很奇怪，只要從新編譯發佈，就不會再出現。這個頗有多是打包問題，還有類加載問題。

查詢github上，社區的人說是類加載問題（https://github.com/spring-cloud/spring-cloud-netflix/issues/3101#issuecomment-463382093），首先對於OpenJDK，曾經有一個Bug(https://bugs.openjdk.java.net/browse/JDK-8172726)： 對於ParallelStream，咱們知道默認是由JDK啓動時默認啓動的大小爲CPU核數減1的CommonForkJoinPool執行。在多線程多類加載器環境下，這個CommonForkJoinPool可能會有Bug，就是調用Thread.contextClassLoader的時候，返回的是第一個使用CommonForkJoinPool的代碼的Classloader，而不是系統根ClassLoader，這樣會致使類找不到。

社區修復了這個Bug，只不過是在下一個大版本，也就是GreenWich上，對於Finchley，並無修復。

咱們考慮兩種解決方案：

1. 升級到GreenWich，這個改動很大，從Finchley到GreenWich，Bean初始化機制，JDBC鏈接池，等等都有了不少變化，短時間內耗時費力。
2. 參考：https://github.com/spring-cloud/spring-cloud-commons/commit/b38ce54410af8fc62d8ae6fe694b580e509ae73a#diff-8c70f107deac71db815f81fa81d5f947，覆蓋源碼，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<String, C> 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);
			//在這裏添加代碼，使用parent的類加載器
			context.setClassLoader(this.parent.getClassLoader());
		}
		context.setDisplayName(generateDisplayName(name));
		context.refresh();
		return context;
	}

這樣也是一種應急方案，短時間內解決問題。留足時間升級。