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
{@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。
到此这篇关于浅谈Spring中@Import注解的作用和使用的文章就介绍到这了,更多相关Spring@Import注解内容请搜索毛票票以前的文章或继续浏览下面的相关文章希望大家以后多多支持毛票票！
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