使用 Idea CE 创建的 Maven Web 项目，启动时却输出以下错误：
Connected to the target VM, address: '127.0.0.1:52165', transport: 'socket'
. ____ _ __ _ _/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v1.4.3.RELEASE)
2017-09-26 11:42:34.121 INFO 2316 --- [ main] Application : Starting Application on avenMac.local with PID 2316 (/Users/aven/Documents/IdeaProject/testboot1/target/classes started by aven in /Users/aven/Documents/IdeaProject/testboot1)
2017-09-26 11:42:34.125 INFO 2316 --- [ main] Application : No active profile set, falling back to default profiles: default
2017-09-26 11:42:34.228 INFO 2316 --- [ main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@479cbee5: startup date [Tue Sep 26 11:42:34 CST 2017]; root of context hierarchy
2017-09-26 11:42:34.302 WARN 2316 --- [ main] ionWarningsApplicationContextInitializer :
** WARNING ** : Your ApplicationContext is unlikely to start due to a @ComponentScan of the default package.
2017-09-26 11:42:47.054 WARN 2316 --- [ main] ationConfigEmbeddedWebApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanDefinitionStoreException: Failed to parse configuration class [Application]; nested exception is org.springframework.context.annotation.ConflictingBeanDefinitionException: Annotation-specified bean name 'errorPageFilter' for bean class [org.springframework.boot.web.support.ErrorPageFilter] conflicts with existing, non-compatible bean definition of same name and class [org.springframework.boot.context.web.ErrorPageFilter]
2017-09-26 11:42:47.061 ERROR 2316 --- [ main] o.s.b.f.s.DefaultListableBeanFactory : Destroy method on bean with name 'org.springframework.boot.autoconfigure.internalCachingMetadataReaderFactory' threw an exception
java.lang.IllegalStateException: ApplicationEventMulticaster not initialized - call 'refresh' before multicasting events via the context: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@479cbee5: startup date [Tue Sep 26 11:42:34 CST 2017]; root of context hierarchy
at org.springframework.context.support.AbstractApplicationContext.getApplicationEventMulticaster(AbstractApplicationContext.java:404) [spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.support.ApplicationListenerDetector.postProcessBeforeDestruction(ApplicationListenerDetector.java:97) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.beans.factory.support.DisposableBeanAdapter.destroy(DisposableBeanAdapter.java:253) ~[spring-beans-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroyBean(DefaultSingletonBeanRegistry.java:578) [spring-beans-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroySingleton(DefaultSingletonBeanRegistry.java:554) [spring-beans-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.destroySingleton(DefaultListableBeanFactory.java:959) [spring-beans-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroySingletons(DefaultSingletonBeanRegistry.java:523) [spring-beans-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.destroySingletons(DefaultListableBeanFactory.java:966) [spring-beans-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.destroyBeans(AbstractApplicationContext.java:1033) [spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:555) [spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122) [spring-boot-1.4.3.RELEASE.jar:1.4.3.RELEASE]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:761) [spring-boot-1.4.3.RELEASE.jar:1.4.3.RELEASE]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:371) [spring-boot-1.4.3.RELEASE.jar:1.4.3.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) [spring-boot-1.4.3.RELEASE.jar:1.4.3.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1186) [spring-boot-1.4.3.RELEASE.jar:1.4.3.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1175) [spring-boot-1.4.3.RELEASE.jar:1.4.3.RELEASE]
at Application.main(Application.java:15) [classes/:na]
2017-09-26 11:42:47.068 ERROR 2316 --- [ main] o.s.boot.SpringApplication : Application startup failed
org.springframework.beans.factory.BeanDefinitionStoreException: Failed to parse configuration class [Application]; nested exception is org.springframework.context.annotation.ConflictingBeanDefinitionException: Annotation-specified bean name 'errorPageFilter' for bean class [org.springframework.boot.web.support.ErrorPageFilter] conflicts with existing, non-compatible bean definition of same name and class [org.springframework.boot.context.web.ErrorPageFilter]
at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:180) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(ConfigurationClassPostProcessor.java:308) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(ConfigurationClassPostProcessor.java:228) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:270) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:93) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:686) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:524) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122) ~[spring-boot-1.4.3.RELEASE.jar:1.4.3.RELEASE]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:761) [spring-boot-1.4.3.RELEASE.jar:1.4.3.RELEASE]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:371) [spring-boot-1.4.3.RELEASE.jar:1.4.3.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) [spring-boot-1.4.3.RELEASE.jar:1.4.3.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1186) [spring-boot-1.4.3.RELEASE.jar:1.4.3.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1175) [spring-boot-1.4.3.RELEASE.jar:1.4.3.RELEASE]
at Application.main(Application.java:15) [classes/:na]
Caused by: org.springframework.context.annotation.ConflictingBeanDefinitionException: Annotation-specified bean name 'errorPageFilter' for bean class [org.springframework.boot.web.support.ErrorPageFilter] conflicts with existing, non-compatible bean definition of same name and class [org.springframework.boot.context.web.ErrorPageFilter]
at org.springframework.context.annotation.ClassPathBeanDefinitionScanner.checkCandidate(ClassPathBeanDefinitionScanner.java:320) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.annotation.ClassPathBeanDefinitionScanner.doScan(ClassPathBeanDefinitionScanner.java:259) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.annotation.ComponentScanAnnotationParser.parse(ComponentScanAnnotationParser.java:137) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.annotation.ConfigurationClassParser.doProcessConfigurationClass(ConfigurationClassParser.java:268) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.annotation.ConfigurationClassParser.processConfigurationClass(ConfigurationClassParser.java:230) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:197) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:166) ~[spring-context-4.3.5.RELEASE.jar:4.3.5.RELEASE]
... 13 common frames omitted
Disconnected from the target VM, address: '127.0.0.1:52165', transport: 'socket'
Process finished with exit code 1
关键部分已经标为红色，但是基于这个错误信息，还是让人摸不着头脑。新建的项目，就添加了几个文件，而且也根本没有和 ErrorPageFilter 重名的啊！
探索1
把 @ComponentScan 干掉了，错误没有了，结果可想而知……
问题原因
Application 类不能没有包名！
解决方法
知道了真实的原因，解决起来就比较简单了。
在 java 目录下新建 package ，然后把
Application 类 拖拽进去就可以了。
