浅谈Spring中@Import注解的作用和使用
@Import用来导入@Configuration注解的配置类、声明@Bean注解的bean方法、导入ImportSelector的实现类或导入ImportBeanDefinitionRegistrar的实现类。
@Import注解的作用
查看Import注解源码
/** *Indicatesoneormore{@linkConfiguration@Configuration}classestoimport. * *Providesfunctionalityequivalenttothe{@code
}elementinSpringXML. *Onlysupportedforclassesannotatedwith{@code@Configuration}ordeclaringatleast *one{@linkBean@Bean}method,aswellas{@linkImportSelector}and *{@linkImportBeanDefinitionRegistrar}implementations. * * {@code@Bean}definitionsdeclaredinimported{@code@Configuration}classes *shouldbeaccessedbyusing{@linkorg.springframework.beans.factory.annotation.Autowired@Autowired} *injection.Eitherthebeanitselfcanbeautowired,ortheconfigurationclassinstance *declaringthebeancanbeautowired.Thelatterapproachallowsforexplicit, *IDE-friendlynavigationbetween{@code@Configuration}classmethods. * *
Maybedeclaredattheclasslevelorasameta-annotation. * *
IfXMLorothernon-{@code@Configuration}beandefinitionresourcesneedtobe *imported,use{@linkImportResource@ImportResource} * *@authorChrisBeams *@since3.0 *@seeConfiguration *@seeImportSelector *@seeImportResource */ @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented public@interfaceImport{ /** *The@{@linkConfiguration},{@linkImportSelector}and/or *{@linkImportBeanDefinitionRegistrar}classestoimport. */ Class>[]value(); }
分析类注释得出结论:
- 声明一个bean
- 导入@Configuration注解的配置类
- 导入ImportSelector的实现类
- 导入ImportBeanDefinitionRegistrar的实现类
@Import注解的使用
声明一个bean
packagecom.example.demo.bean; publicclassTestBean1{ } packagecom.example.demo; importcom.example.demo.bean.TestBean1; importorg.springframework.context.annotation.Configuration; importorg.springframework.context.annotation.Import; @Import({TestBean1.class}) @Configuration publicclassAppConfig{ }
导入@Configuration注解的配置类
packagecom.example.demo.bean; publicclassTestBean2{ } packagecom.example.demo.bean; importorg.springframework.context.annotation.Bean; importorg.springframework.context.annotation.Configuration; @Configuration publicclassTestConfig{ @Bean publicTestBean2getTestBean2(){ returnnewTestBean2(); } } packagecom.example.demo; importcom.example.demo.bean.TestBean1; importcom.example.demo.bean.TestConfig; importorg.springframework.context.annotation.Configuration; importorg.springframework.context.annotation.Import; @Import({TestBean1.class,TestConfig.class}) @Configuration publicclassAppConfig{ }
导入ImportSelector的实现类
packagecom.example.demo.bean; publicclassTestBean3{ } packagecom.example.demo.bean; importorg.springframework.context.annotation.ImportSelector; importorg.springframework.core.type.AnnotationMetadata; publicclassTestImportSelectorimplementsImportSelector{ @Override publicString[]selectImports(AnnotationMetadataimportingClassMetadata){ returnnewString[]{"com.example.demo.bean.TestBean3"}; } } packagecom.example.demo; importcom.example.demo.bean.TestBean1; importcom.example.demo.bean.TestConfig; importcom.example.demo.bean.TestImportSelector; importorg.springframework.context.annotation.Configuration; importorg.springframework.context.annotation.Import; @Import({TestBean1.class,TestConfig.class,TestImportSelector.class}) @Configuration publicclassAppConfig{ }
导入ImportBeanDefinitionRegistrar的实现类
packagecom.example.demo.bean; publicclassTestBean4{ } packagecom.example.demo.bean; importorg.springframework.beans.factory.support.BeanDefinitionRegistry; importorg.springframework.beans.factory.support.RootBeanDefinition; importorg.springframework.context.annotation.ImportBeanDefinitionRegistrar; importorg.springframework.core.type.AnnotationMetadata; publicclassTestImportBeanDefinitionRegistrarimplementsImportBeanDefinitionRegistrar{ @Override publicvoidregisterBeanDefinitions(AnnotationMetadataimportingClassMetadata,BeanDefinitionRegistryregistry){ RootBeanDefinitionrootBeanDefinition=newRootBeanDefinition(TestBean4.class); registry.registerBeanDefinition("TestBean4",rootBeanDefinition); } } packagecom.example.demo; importcom.example.demo.bean.TestBean1; importcom.example.demo.bean.TestConfig; importcom.example.demo.bean.TestImportBeanDefinitionRegistrar; importcom.example.demo.bean.TestImportSelector; importorg.springframework.context.annotation.Configuration; importorg.springframework.context.annotation.Import; @Import({TestBean1.class,TestConfig.class,TestImportSelector.class,TestImportBeanDefinitionRegistrar.class}) @Configuration publicclassAppConfig{ }
最后,我们来看下导入结果:
packagecom.example.demo; importorg.junit.Test; importorg.junit.runner.RunWith; importorg.springframework.boot.test.context.SpringBootTest; importorg.springframework.context.annotation.AnnotationConfigApplicationContext; importorg.springframework.test.context.junit4.SpringRunner; importjava.util.Arrays; @RunWith(SpringRunner.class) @SpringBootTest publicclassDemoApplicationTests{ @Test publicvoidtest(){ AnnotationConfigApplicationContextannotationConfigApplicationContext=newAnnotationConfigApplicationContext(AppConfig.class); String[]beanDefinitionNames=annotationConfigApplicationContext.getBeanDefinitionNames(); System.out.println("--------------------------------------------------------"); for(StringbeanDefinitionName:beanDefinitionNames){ System.out.println(beanDefinitionName); } System.out.println("--------------------------------------------------------"); } }
打印结果如下:
--------------------------------------------------------
org.springframework.context.annotation.internalConfigurationAnnotationProcessor
org.springframework.context.annotation.internalAutowiredAnnotationProcessor
org.springframework.context.annotation.internalRequiredAnnotationProcessor
org.springframework.context.annotation.internalCommonAnnotationProcessor
org.springframework.context.event.internalEventListenerProcessor
org.springframework.context.event.internalEventListenerFactory
appConfig
com.example.demo.bean.TestBean1
com.example.demo.bean.TestConfig
getTestBean2
com.example.demo.bean.TestBean3
TestBean4
--------------------------------------------------------
可以看出TestBean1,TestBean2,TestBean3,TestBean4通过不同的4种导入方法被导入SpringIOC容器中。
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