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<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。
