项目中引入了dubbo-spring-boot-starter
version=2.7.1，其中中有一个配置类是以FactoryBean的形式加载到Spring 容器中，该配置类只有一个含参构造器，此时会触发一个异常：
`Caused by: java.lang.NoSuchMethodException:
com.abakus.user.web.StringFactoryBean.<init>()`
该配置类示例如下：
`
@Component
@RequiredArgsConstructor
public class StringFactoryBean implements FactoryBean<String> {
private final ObjectMapper objectMapper;
@Override
public String getObject() throws Exception {
return "";
}
@Override
public Class<?> getObjectType() {
return String.class;
}
}
`
异常栈信息如下所示：
`org.springframework.beans.factory.BeanCreationException: Error creating bean
with name 'stringFactoryBean' defined in file [/*/*/*/StringFactoryBean.class]:
Instantiation of bean failed; nested exception is
org.springframework.beans.BeanInstantiationException: Failed to instantiate
[*.*.*.StringFactoryBean]: No default constructor found; nested exception is
java.lang.NoSuchMethodException: *.*.*.StringFactoryBean.<init>()
at
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1270)
at
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1164)
at
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.getSingletonFactoryBeanForTypeCheck(AbstractAutowireCapableBeanFactory.java:974)
at
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.getTypeForFactoryBean(AbstractAutowireCapableBeanFactory.java:848)
at
org.springframework.beans.factory.support.AbstractBeanFactory.isTypeMatch(AbstractBeanFactory.java:574)
at
org.springframework.beans.factory.support.DefaultListableBeanFactory.doGetBeanNamesForType(DefaultListableBeanFactory.java:514)
at
org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanNamesForType(DefaultListableBeanFactory.java:477)
at
org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanNamesForType(DefaultListableBeanFactory.java:471)
at
org.springframework.beans.factory.BeanFactoryUtils.beanNamesForTypeIncludingAncestors(BeanFactoryUtils.java:190)
at
org.apache.dubbo.spring.boot.beans.factory.config.DubboConfigBeanDefinitionConflictProcessor.resolveUniqueApplicationConfigBean(DubboConfigBeanDefinitionConflictProcessor.java:78)
at
org.apache.dubbo.spring.boot.beans.factory.config.DubboConfigBeanDefinitionConflictProcessor.postProcessBeanFactory(DubboConfigBeanDefinitionConflictProcessor.java:63)
at
org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:286)
at
org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:130)
at
org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:691)
at
org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:528)
at
org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:142)
at
org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775)
at
org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397)
at
org.springframework.boot.SpringApplication.run(SpringApplication.java:316)
at com.abakus.user.StartApp.main(StartApp.java:30)
Caused by: org.springframework.beans.BeanInstantiationException: Failed to
instantiate [*.*.*.StringFactoryBean]: No default constructor found; nested
exception is java.lang.NoSuchMethodException:
com.abakus.user.web.StringFactoryBean.<init>()
at
org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:83)
at
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1262)
... 19 common frames omitted
Caused by: java.lang.NoSuchMethodException: *.*.*.StringFactoryBean.<init>()
at java.lang.Class.getConstructor0(Class.java:3082)
at java.lang.Class.getDeclaredConstructor(Class.java:2178)
at
org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:78)
... 20 common frames omitted`
根据我的研究，得出以下结论：DubboConfigBeanDefinitionConflictProcessor会从spring容器中获取ApplicationConfig.class
的所有beanName，对于FactoryBean的beanType会先获取该实例，然而对于含参构造器的spring容器类的实例化需要AutowiredAnnotationBeanPostProcessor的辅助。不过当DubboConfigBeanDefinitionConflictProcessor被调用的时候AutowiredAnnotationBeanPostProcessor还未被加载到spring容器内，所以触发上述异常。
[ Full content available at:
https://github.com/apache/dubbo-spring-boot-project/issues/638 ]
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