使用Spring的component-scan来自定义Bean的命名

在使用Spring Boot的component-scan进行开发时（即使是默认配置），由于自动命名Bean，很容易发生命名冲突的情况。

SampleSpringBoot
├── SampleSpringBootApplication.java
└── controller
    ├── fuga
    │   └── HelloController.java
    └── hoge
        └── HelloController.java

在这种情况下，无论是fuga.HelloController还是hoge.HelloController都会被命名为helloController Bean，并且由于重名而无法启动。

org.springframework.beans.factory.BeanDefinitionStoreException: Failed to parse configuration class [net.sinsengumi.SampleSpringBoot.SampleSpringBootApplication]; nested exception is org.springframework.context.annotation.ConflictingBeanDefinitionException: Annotation-specified bean name 'helloController' for bean class [net.sinsengumi.SampleSpringBoot.controller.hoge.HelloController] conflicts with existing, non-compatible bean definition of same name and class [net.sinsengumi.SampleSpringBoot.controller.fuga.HelloController]
    at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:181) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(ConfigurationClassPostProcessor.java:308) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(ConfigurationClassPostProcessor.java:228) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:270) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:93) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:687) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:525) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122) ~[spring-boot-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:693) [spring-boot-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:360) [spring-boot-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) [spring-boot-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1118) [spring-boot-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1107) [spring-boot-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at net.sinsengumi.SampleSpringBoot.SampleSpringBootApplication.main(SampleSpringBootApplication.java:10) [classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_112]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_112]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_112]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_112]
    at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-1.5.4.RELEASE.jar:1.5.4.RELEASE]
Caused by: org.springframework.context.annotation.ConflictingBeanDefinitionException: Annotation-specified bean name 'helloController' for bean class [net.sinsengumi.SampleSpringBoot.controller.hoge.HelloController] conflicts with existing, non-compatible bean definition of same name and class [net.sinsengumi.SampleSpringBoot.controller.fuga.HelloController]
    at org.springframework.context.annotation.ClassPathBeanDefinitionScanner.checkCandidate(ClassPathBeanDefinitionScanner.java:345) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.annotation.ClassPathBeanDefinitionScanner.doScan(ClassPathBeanDefinitionScanner.java:283) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.annotation.ComponentScanAnnotationParser.parse(ComponentScanAnnotationParser.java:135) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.annotation.ConfigurationClassParser.doProcessConfigurationClass(ConfigurationClassParser.java:287) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.annotation.ConfigurationClassParser.processConfigurationClass(ConfigurationClassParser.java:245) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:198) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:167) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    ... 18 common frames omitted

如果想要避免这个问题，只需要在定义 Component 时设置一个 Bean 名称即可。

// fuga.HelloController
@RestController("fugaHelloController")

// hoge.HelloController
@RestController("hogeHelloController")

然而，这样的事情实在太繁琐了，最好一次性进行设置，且保证不重复。可以使用 component-scan 的 nameGenerator 来实现。
一般情况下，如果要确保不重复，我想到的是使用完全限定类名（FQCN）。而且，我认为这样就没有问题了。

public class FQCNBeanNameGenerator extends AnnotationBeanNameGenerator {

    @Override
    protected String buildDefaultBeanName(BeanDefinition definition) {
        return definition.getBeanClassName();
    }
}

@SpringBootApplication
@ComponentScan(nameGenerator = FQCNBeanNameGenerator.class)
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

现在，`Bean` 名称为`net.sinsengumi.SampleSpringBoot.controller.fuga.HelloController`和`net.sinsengumi.SampleSpringBoot.controller.hoge.HelloController`之间不会再出现重复。

春天希望将此行为设为默认选项。