When Spring beans name are duplicated, when will an exception be thrown?

Question

It confuses me that when I use the @Bean method to inject two beans with the same name into the container and start the Spring application context, it succeeds. However, if I use @Component to inject two beans with the same name into the container and start the context, it throws an exception. Why does this happen, and how should I understand it?

example1: the method named beanA will execute and beanB will be ignored, start Spring application context will succeed. It alwalys execute above method?

@SpringBootApplication
public class LuckySpringBootStarterApplication {

    @Bean(name = "a")
    public String beanA() {
        return "a";
    }

    @Bean(name = "a")
    public String beanB() {
        return "b";
    }

    public static void main(String[] args) {
        SpringApplication.run(LuckySpringBootStarterApplication.class, args);
    }
}

example2 will throw an exception

@SpringBootApplication
public class LuckySpringBootStarterApplication {

    @Component("a")
    static class A {

    }

    @Component("a")
    static class B {

    }

    public static void main(String[] args) {
        SpringApplication.run(LuckySpringBootStarterApplication.class, args);
    }
}

org.springframework.beans.factory.BeanDefinitionStoreException: Failed to parse configuration class [space.luckycurve.LuckySpringBootStarterApplication]
    at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:179) ~[spring-context-6.1.11.jar:6.1.11]
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(ConfigurationClassPostProcessor.java:417) ~[spring-context-6.1.11.jar:6.1.11]
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(ConfigurationClassPostProcessor.java:290) ~[spring-context-6.1.11.jar:6.1.11]
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:349) ~[spring-context-6.1.11.jar:6.1.11]
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:118) ~[spring-context-6.1.11.jar:6.1.11]
    at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:789) ~[spring-context-6.1.11.jar:6.1.11]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:607) ~[spring-context-6.1.11.jar:6.1.11]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:146) ~[spring-boot-3.3.2.jar:3.3.2]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:754) ~[spring-boot-3.3.2.jar:3.3.2]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:456) ~[spring-boot-3.3.2.jar:3.3.2]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:335) ~[spring-boot-3.3.2.jar:3.3.2]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1363) ~[spring-boot-3.3.2.jar:3.3.2]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1352) ~[spring-boot-3.3.2.jar:3.3.2]
    at space.luckycurve.LuckySpringBootStarterApplication.main(LuckySpringBootStarterApplication.java:21) ~[classes/:na]
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:580) ~[na:na]
    at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:50) ~[spring-boot-devtools-3.3.2.jar:3.3.2]
Caused by: org.springframework.context.annotation.ConflictingBeanDefinitionException: Annotation-specified bean name 'a' for bean class [space.luckycurve.LuckySpringBootStarterApplication$B] conflicts with existing, non-compatible bean definition of same name and class [space.luckycurve.LuckySpringBootStarterApplication$A]
    at org.springframework.context.annotation.ClassPathBeanDefinitionScanner.checkCandidate(ClassPathBeanDefinitionScanner.java:361) ~[spring-context-6.1.11.jar:6.1.11]
    at org.springframework.context.annotation.ClassPathBeanDefinitionScanner.doScan(ClassPathBeanDefinitionScanner.java:288) ~[spring-context-6.1.11.jar:6.1.11]
    at org.springframework.context.annotation.ComponentScanAnnotationParser.parse(ComponentScanAnnotationParser.java:128) ~[spring-context-6.1.11.jar:6.1.11]
    at org.springframework.context.annotation.ConfigurationClassParser.doProcessConfigurationClass(ConfigurationClassParser.java:306) ~[spring-context-6.1.11.jar:6.1.11]
    at org.springframework.context.annotation.ConfigurationClassParser.processConfigurationClass(ConfigurationClassParser.java:246) ~[spring-context-6.1.11.jar:6.1.11]
    at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:197) ~[spring-context-6.1.11.jar:6.1.11]
    at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:165) ~[spring-context-6.1.11.jar:6.1.11]
    ... 16 common frames omitted

Answer 1

I have submitted an issue in spring framework and this issue added to the 6.2.0-M7 milestone, You can check the latest progress through the following link: https://github.com/spring-projects/spring-framework/issues/33330