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
/** * Indicates one or more {@link Configuration @Configuration} classes to import. * * <p>Provides functionality equivalent to the {@code <import/>} element in Spring XML. * Only supported for classes annotated with {@code @Configuration} or declaring at least * one {@link Bean @Bean} method, as well as {@link ImportSelector} and * {@link ImportBeanDefinitionRegistrar} implementations. * * <p>{@code @Bean} definitions declared in imported {@code @Configuration} classes * should be accessed by using {@link org.springframework.beans.factory.annotation.Autowired @Autowired} * injection. Either the bean itself can be autowired, or the configuration class instance * declaring the bean can be autowired. The latter approach allows for explicit, * IDE-friendly navigation between {@code @Configuration} class methods. * * <p>May be declared at the class level or as a meta-annotation. * * <p>If XML or other non-{@code @Configuration} bean definition resources need to be * imported, use {@link ImportResource @ImportResource} * * @author Chris Beams * @since 3.0 * @see Configuration * @see ImportSelector * @see ImportResource */ @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface Import { /** * The @{@link Configuration}, {@link ImportSelector} and/or * {@link ImportBeanDefinitionRegistrar} classes to import. */ 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
package com.example.demo.bean; public class TestBean1 { } package com.example.demo; import com.example.demo.bean.TestBean1; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Import; @Import({TestBean1.class}) @Configuration public class AppConfig { }
导入@Configuration注解的配置类
package com.example.demo.bean; public class TestBean2 { } package com.example.demo.bean; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class TestConfig { @Bean public TestBean2 getTestBean2(){ return new TestBean2(); } } package com.example.demo; import com.example.demo.bean.TestBean1; import com.example.demo.bean.TestConfig; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Import; @Import({TestBean1.class,TestConfig.class}) @Configuration public class AppConfig { }
导入ImportSelector的实现类
package com.example.demo.bean; public class TestBean3 { } package com.example.demo.bean; import org.springframework.context.annotation.ImportSelector; import org.springframework.core.type.AnnotationMetadata; public class TestImportSelector implements ImportSelector { @Override public String[] selectImports(AnnotationMetadata importingClassMetadata) { return new String[]{"com.example.demo.bean.TestBean3"}; } } package com.example.demo; import com.example.demo.bean.TestBean1; import com.example.demo.bean.TestConfig; import com.example.demo.bean.TestImportSelector; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Import; @Import({TestBean1.class,TestConfig.class,TestImportSelector.class}) @Configuration public class AppConfig { }
导入ImportBeanDefinitionRegistrar的实现类
package com.example.demo.bean; public class TestBean4 { } package com.example.demo.bean; import org.springframework.beans.factory.support.BeanDefinitionRegistry; import org.springframework.beans.factory.support.RootBeanDefinition; import org.springframework.context.annotation.ImportBeanDefinitionRegistrar; import org.springframework.core.type.AnnotationMetadata; public class TestImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar { @Override public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { RootBeanDefinition rootBeanDefinition = new RootBeanDefinition(TestBean4.class); registry.registerBeanDefinition("TestBean4", rootBeanDefinition); } } package com.example.demo; import com.example.demo.bean.TestBean1; import com.example.demo.bean.TestConfig; import com.example.demo.bean.TestImportBeanDefinitionRegistrar; import com.example.demo.bean.TestImportSelector; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Import; @Import({TestBean1.class,TestConfig.class,TestImportSelector.class,TestImportBeanDefinitionRegistrar.class}) @Configuration public class AppConfig { }
最后,我们来看下导入结果:
package com.example.demo; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.boot.test.context.SpringBootTest; import org.springframework.context.annotation.AnnotationConfigApplicationContext; import org.springframework.test.context.junit4.SpringRunner; import java.util.Arrays; @RunWith(SpringRunner.class) @SpringBootTest public class DemoApplicationTests { @Test public void test() { AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(AppConfig.class); String[] beanDefinitionNames = annotationConfigApplicationContext.getBeanDefinitionNames(); System.out.println("--------------------------------------------------------"); for (String beanDefinitionName: 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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