[Bug] Spring相关bug收集

1. RequiredArgsConstructor空指针错误

2.TestRestTemplate注入时异常NoSuchBeanDefinitionException

3. 错误信息：Your ApplicationContext is unlikely to start due to a @ComponentScan of the default package.

4.factory-bean reference points back to the same bean definition

1. `RequiredArgsConstructor空指针错误`

定义了一个类，用以下注解修饰

@Service("ABC")
@RequiredArgsConstructor(onConstructor = @__(@Autowired))

拿掉@RequiredArgsConstructor(onConstructor = @__(@Autowired))这个注解之后报空指针错

ABC这个bean没有注入进去

@NoArgsConstructor, @RequiredArgsConstructor, @AllArgsContructor。是Lombok插件三种生成不同构造方法的注解，来完成项目中不同构造方法的需求。

@RequiredArgsConstructor的作用是: 会生成一个包含常量，和标识了NotNull的变量的构造方法。生成的构造方法是私有的private

2.TestRestTemplate注入时异常NoSuchBeanDefinitionException

错误信息如下:

Unsatisfied dependency expressed through field 'testRestTemplate'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'org.springframework.boot.test.web.client.TestRestTemplate' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

解决方式：在spring test的启动类里面将启动类的注解的SpringBootTest注解改为如下即可：
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)

3. 错误信息：Your ApplicationContext is unlikely to start due to a @ComponentScan of the default package.

在自己新建一个maven项目之后，引入了spring的相关依赖，随即在java包当中写了一个spring boot的启动类，但是在启动时报了如下错误：

** WARNING ** : Your ApplicationContext is unlikely to start due to a @ComponentScan of the default package.2019-03-13 22:23:48.872  WARN 7753 --- [           main] ConfigServletWebServerApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanDefinitionStoreException: Failed to parse configuration class [Application]; nested exception is java.io.FileNotFoundException: class path resource [org/springframework/web/socket/config/annotation/WebSocketMessageBrokerConfigurer.class] cannot be opened because it does not exist
2019-03-13 22:23:48.885  INFO 7753 --- [           main] ConditionEvaluationReportLoggingListener : Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2019-03-13 22:23:48.895 ERROR 7753 --- [           main] o.s.boot.SpringApplication               : Application run failedorg.springframework.beans.factory.BeanDefinitionStoreException: Failed to parse configuration class [Application]; nested exception is java.io.FileNotFoundException: class path resource [org/springframework/web/socket/config/annotation/WebSocketMessageBrokerConfigurer.class] cannot be opened because it does not existat org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:184) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(ConfigurationClassPostProcessor.java:316) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(ConfigurationClassPostProcessor.java:233) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:273) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:93) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:694) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:532) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) ~[spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:759) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:395) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]at org.springframework.boot.SpringApplication.run(SpringApplication.java:327) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]at org.springframework.boot.SpringApplication.run(SpringApplication.java:1255) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]at org.springframework.boot.SpringApplication.run(SpringApplication.java:1243) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]at Application.main(Application.java:7) [classes/:na]
Caused by: java.io.FileNotFoundException: class path resource [org/springframework/web/socket/config/annotation/WebSocketMessageBrokerConfigurer.class] cannot be opened because it does not existat org.springframework.core.io.ClassPathResource.getInputStream(ClassPathResource.java:180) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.core.type.classreading.SimpleMetadataReader.<init>(SimpleMetadataReader.java:51) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.core.type.classreading.SimpleMetadataReaderFactory.getMetadataReader(SimpleMetadataReaderFactory.java:103) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.boot.type.classreading.ConcurrentReferenceCachingMetadataReaderFactory.createMetadataReader(ConcurrentReferenceCachingMetadataReaderFactory.java:88) ~[spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]at org.springframework.boot.type.classreading.ConcurrentReferenceCachingMetadataReaderFactory.getMetadataReader(ConcurrentReferenceCachingMetadataReaderFactory.java:75) ~[spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]at org.springframework.core.type.classreading.SimpleMetadataReaderFactory.getMetadataReader(SimpleMetadataReaderFactory.java:81) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.annotation.ConfigurationClassParser.asSourceClass(ConfigurationClassParser.java:734) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.annotation.ConfigurationClassParser$SourceClass.getInterfaces(ConfigurationClassParser.java:963) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.annotation.ConfigurationClassParser.processInterfaces(ConfigurationClassParser.java:376) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.annotation.ConfigurationClassParser.doProcessConfigurationClass(ConfigurationClassParser.java:324) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.annotation.ConfigurationClassParser.processConfigurationClass(ConfigurationClassParser.java:245) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:194) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.annotation.ConfigurationClassParser.doProcessConfigurationClass(ConfigurationClassParser.java:296) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.annotation.ConfigurationClassParser.processConfigurationClass(ConfigurationClassParser.java:245) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:202) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:170) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]... 13 common frames omitted

这个错误提示的是WebSocketMessageBrokerConfigurer相关的错误，我非常纳闷，我什么逻辑都没写怎么会报这个错了，又注意到了一条警告信息：ApplicationConetext没有启动。猜测应该是springboot自动配置相关。于是上google上一搜，发现了原因是因为spring boot的启动类必须放在某一个具体的包下面。

这是错误的方式：

这才是正确的方式：

进一步分析原因，熟悉spring boot自动装配原理的朋友应该知道spring boot的自动配置是基于注解@SpringbootApplication的，而这个注解是以它所修饰的类也就是这里的Application类，所在的包的位置去决定scan扫描哪些包的。因此当Application不在一个包下面时，我们的component scan就没有生效而我们自己定义的配置也就不会生效。

更多的信息可以参考stackover flow上的这个问题：链接。

4.factory-bean reference points back to the same bean definition

源代码定义如下：

@Configuration
public class TargetDataSource {@Bean("targetDataSource")@ConfigurationProperties(prefix="spring.datasource.target")public DataSource dataSource() {return DataSourceBuilder.create().build();}}

在运行的时候报错：

Caused by: org.springframework.beans.factory.BeanDefinitionStoreException: Invalid bean definition with name 'targetDataSource' defined in class path resource [com/sap/ngom/datamigration/configuration/TargetDataSource.class]: factory-bean reference points back to the same bean definitionat org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.getTypeForFactoryMethod(AbstractAutowireCapableBeanFactory.java:705)at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.determineTargetType(AbstractAutowireCapableBeanFactory.java:669)at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.predictBeanType(AbstractAutowireCapableBeanFactory.java:637)at org.springframework.beans.factory.support.AbstractBeanFactory.isFactoryBean(AbstractBeanFactory.java:1489)at org.springframework.beans.factory.support.DefaultListableBeanFactory.doGetBeanNamesForType(DefaultListableBeanFactory.java:420)at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanNamesForType(DefaultListableBeanFactory.java:390)at org.springframework.beans.factory.BeanFactoryUtils.beanNamesForTypeIncludingAncestors(BeanFactoryUtils.java:222)at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1276)at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1101)at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1065)at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:815)at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:721)

原因在于这里的Class也是一个bean，datasource也是一个bean，而且他们的名字一样，在修改名字不一样之后，错误消失。

5.Failed to bind properties under '' to com.zaxxer.hikari.HikariDataSource:

启动spring boot应用程序时报错如下

***************************
APPLICATION FAILED TO START
***************************Description:Failed to bind properties under '' to com.zaxxer.hikari.HikariDataSource:Property: driverclassnameValue: org.h2.DriverOrigin: "driverClassName" from property source "source"Reason: Unable to set value for property driver-class-nameAction:

原因在于代码中定义了h2数据库的bean，但是却缺少相关的maven依赖。去掉之后错误消失。