冲突分析
如果我们希望将相同名称的类放入spring中时，如果未指定bean名称，则会抛出异常：
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源码得知，当我们使用注解创建bean时，spring使用了AnnotationBeanNameGenerator来创建bean的名称。
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);
如果我们项目中存在相同名称的类，而在使用注解时（@Service、@Component）指定了不同的name，则不会抛出异常，否则Spring使用类的名称作为bean的名称，则会抛出异常。
但有些特殊场景，如多版本模块，我们不希望版本号污染类名，而希望以包的形式控制。则此时我们需要替换spring的默认名称生成器。
- com.v1
- UserController
- com.v2
- UserController
冲突解决
创建全类名的BeanNameGenerator
此处代码摘自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提供了在启动时传入BeanNameGenerator的方式，可以修改Spring扫描注解时使用的名称。
@SpringBootApplication
@ComponentScan(nameGenerator = AnnotationBeanNameGenerator.class)
Mybatis
而Mybatis并不是由Spring直接扫描的，而是由其本身自主扫描到Mapper而注入到Spring中。关键代码如下:
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
AnnotationAttributes annoAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
.....
.....
}
mybatis创建了spring提供的ClassPathMapperScanner，其默认使用的扔是AnnotationBeanNameGenerator。而mybatis也提供了修改方式。
@MapperScan(nameGenerator = AnnotationBeanNameGenerator.class)
SpringBoot && Mybatis
完整代码如下:
@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);
}
}
暴力覆盖方案
上述方式到是一般情况下足够了，但如果此时项目中又存在一个类似mybatis的组件，那么你仍需要配置BeanNameGenerator。我们可以暴力覆盖原本的AnnotationBeanNameGenerator，
建立与其包名相同，类名相同的文件在项目中：
image.png
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"));
}
}
此时无须配置任何配置，默认会走此BeanNameGenerator。
