Spring Bean名稱重復ConflictingBeanDefinitionException解決

沖突分析

如果我們希望將相同名稱的類放入spring中時，如果未指定bean名稱，則會拋出異常：

Caused by: org.springframework.context.annotation.ConflictingBeanDefinitionException: Annotation-specified bean name 'xxxx' for bean class [xxx] conflicts with existing, non-compatible bean definition of same name and class [xxx] 

翻看Spring源碼得知，當我們使用注解創建bean時，spring使用了AnnotationBeanNameGenerator來創建bean的名稱。

        if (definition instanceof AnnotatedBeanDefinition) { String beanName = determineBeanNameFromAnnotation((AnnotatedBeanDefinition) definition); if (StringUtils.hasText(beanName)) { // Explicit bean name found. return beanName; } } // Fallback: generate a unique default bean name. return buildDefaultBeanName(definition, registry); 

如果我們項目中存在相同名稱的類，而在使用注解時（@Service、@Component）指定了不同的name，則不會拋出異常，否則Spring使用類的名稱作為bean的名稱，則會拋出異常。

但有些特殊場景，如多版本模塊，我們不希望版本號污染類名，而希望以包的形式控制。則此時我們需要替換spring的默認名稱生成器。

- com.v1
    - UserController
- com.v2
    - UserController

沖突解決

創建全類名的BeanNameGenerator

此處代碼摘自ConfigurationClassPostProcessor.importBeanNameGenerator。

public class AnnotationBeanNameGenerator implements BeanNameGenerator { @Override public String generateBeanName(BeanDefinition definition, BeanDefinitionRegistry registry) { if (definition instanceof AnnotatedBeanDefinition) { String beanName = determineBeanNameFromAnnotation((AnnotatedBeanDefinition) definition); if (StringUtils.hasText(beanName)) { // Explicit bean name found. return beanName; } } String beanClassName = definition.getBeanClassName(); Assert.state(beanClassName != null, "No bean class name set"); return beanClassName; } } 

Spring Boot

SpringBoot提供了在啟動時傳入BeanNameGenerator的方式，可以修改Spring掃描注解時使用的名稱。

@SpringBootApplication @ComponentScan(nameGenerator = AnnotationBeanNameGenerator.class) 

Mybatis

而Mybatis並不是由Spring直接掃描的，而是由其本身自主掃描到Mapper而注入到Spring中。關鍵代碼如下:

  @Override public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { AnnotationAttributes annoAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName())); ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry); ..... ..... } 

mybatis創建了spring提供的ClassPathMapperScanner，其默認使用的扔是AnnotationBeanNameGenerator。而mybatis也提供了修改方式。

@MapperScan(nameGenerator = AnnotationBeanNameGenerator.class) 

SpringBoot && Mybatis

完整代碼如下:

@SpringBootApplication @ComponentScan(nameGenerator = Application.SpringBeanNameGenerator.class) @MapperScan(value = "**.mapper", markerInterface = BaseMapper.class, nameGenerator = Application.SpringBeanNameGenerator.class) public class Application { public static class SpringBeanNameGenerator extends AnnotationBeanNameGenerator { @Override protected String buildDefaultBeanName(BeanDefinition definition) { if (definition instanceof AnnotatedBeanDefinition) { String beanName = determineBeanNameFromAnnotation((AnnotatedBeanDefinition) definition); if (StringUtils.hasText(beanName)) { // Explicit bean name found. return beanName; } } return definition.getBeanClassName(); } } public static void main(String[] args) { SpringApplication.run(Application.class, args); } } 

暴力覆蓋方案

上述方式到是一般情況下足夠了，但如果此時項目中又存在一個類似mybatis的組件，那么你仍需要配置BeanNameGenerator。我們可以暴力覆蓋原本的AnnotationBeanNameGenerator，
建立與其包名相同，類名相同的文件在項目中：

 

 

 

 

 

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public class AnnotationBeanNameGenerator implements BeanNameGenerator { private static final String COMPONENT_ANNOTATION_CLASSNAME = "org.springframework.stereotype.Component"; @Override public String generateBeanName(BeanDefinition definition, BeanDefinitionRegistry registry) { if (definition instanceof AnnotatedBeanDefinition) { String beanName = determineBeanNameFromAnnotation((AnnotatedBeanDefinition) definition); if (StringUtils.hasText(beanName)) { // Explicit bean name found. return beanName; } } return definition.getBeanClassName(); } /** * Derive a bean name from one of the annotations on the class. * * @param annotatedDef the annotation-aware bean definition * @return the bean name, or {@code null} if none is found */ protected String determineBeanNameFromAnnotation(AnnotatedBeanDefinition annotatedDef) { AnnotationMetadata amd = annotatedDef.getMetadata(); Set<String> types = amd.getAnnotationTypes(); String beanName = null; for (String type : types) { AnnotationAttributes attributes = AnnotationConfigUtils.attributesFor(amd, type); if (isStereotypeWithNameValue(type, amd.getMetaAnnotationTypes(type), attributes)) { Object value = attributes.get("value"); if (value instanceof String) { String strVal = (String) value; if (StringUtils.hasLength(strVal)) { if (beanName != null && !strVal.equals(beanName)) { throw new IllegalStateException("Stereotype annotations suggest inconsistent " + "component names: '" + beanName + "' versus '" + strVal + "'"); } beanName = strVal; } } } } return beanName; } /** * Check whether the given annotation is a stereotype that is allowed * to suggest a component name through its annotation {@code value()}. * * @param annotationType the name of the annotation class to check * @param metaAnnotationTypes the names of meta-annotations on the given annotation * @param attributes the map of attributes for the given annotation * @return whether the annotation qualifies as a stereotype with component name */ protected boolean isStereotypeWithNameValue(String annotationType, Set<String> metaAnnotationTypes, Map<String, Object> attributes) { boolean isStereotype = annotationType.equals(COMPONENT_ANNOTATION_CLASSNAME) || (metaAnnotationTypes != null && metaAnnotationTypes.contains(COMPONENT_ANNOTATION_CLASSNAME)) || annotationType.equals("javax.annotation.ManagedBean") || annotationType.equals("javax.inject.Named"); return (isStereotype && attributes != null && attributes.containsKey("value")); } } 

此時無須配置任何配置，默認會走此BeanNameGenerator。

版本控制

作者：BeRicher
鏈接：https://www.jianshu.com/p/74c801fd70f4
來源：簡書
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