上文介绍了通过xml配置、注解（@Component、@Controller、@Service、@Repository等）将指定的 bean 注入到 Spring 容器中，后面又介绍了通过 @Configuration 与 @Bean 这两个注解配合使用来将原来配置在 xml 文件里的 Bean 通过 Java 代码的方式将 Bean 注入到 Spring 容器中。

今天，介绍第三种注入 spring 容器的方法：@Import

@Import的作用：

1. @Import 用来导入 @Configuration 注解的配置类、注入普通类。
2. 导入ImportSelector的实现类。
3. 导入ImportBeanDefinitionRegistrar的实现类。

导入普通的POJO

1、新建类Stu1：

package impotTest.pojo;public class Stu1 {
}

2、新建@Import注解修饰配置类MyImport ：

package impotTest.pojo.imports;
...@Configuration
@Import({Stu1.class})
public class MyImport {
}

3、测试类：

public class App 
{public static void main( String[] args ){ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");String[] beanDefinitionNames = context.getBeanDefinitionNames();for (String name : beanDefinitionNames) {System.out.println(name + ":" + context.getBean(name));}System.out.println("++++++++++++++");MyImport myImport = (MyImport) context.getBean("myImport");System.out.println(myImport);Object bean1 = context.getBean("impotTest.pojo.Stu1");System.out.println(bean1);}
}

运行结果：

org.springframework.context.annotation.internalConfigurationAnnotationProcessor: org.springframework.context.annotation.ConfigurationClassPostProcessor@17046283
org.springframework.context.annotation.internalAutowiredAnnotationProcessor: org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor@5bd03f44
org.springframework.context.annotation.internalCommonAnnotationProcessor: org.springframework.context.annotation.CommonAnnotationBeanPostProcessor@29626d54
org.springframework.context.event.internalEventListenerProcessor: org.springframework.context.event.EventListenerMethodProcessor@5a63f509
org.springframework.context.event.internalEventListenerFactory: org.springframework.context.event.DefaultEventListenerFactory@6e4784bc
org.springframework.aop.config.internalAutoProxyCreator: proxyTargetClass=false; optimize=false; opaque=false; exposeProxy=false; frozen=false
myImport: impotTest.pojo.imports.MyImport$$EnhancerBySpringCGLIB$$e2546f15@70e8f8e
impotTest.pojo.Stu1: impotTest.pojo.Stu1@34b7ac2f
++++++++++++++
impotTest.pojo.imports.MyImport$$EnhancerBySpringCGLIB$$e2546f15@70e8f8e
impotTest.pojo.Stu1@34b7ac2f

注入的类Stu1均是以全类名（impotTest.pojo.Stu1）作为name注册到了容器中。

实现ImportSelector的方式

1、新建类Stu2：

package impotTest.pojo;public class Stu2 {
}

2、新建MyImportSelector 实现ImportSelector

package impotTest.pojo.imports;
...public class MyImportSelector implements ImportSelector {@Overridepublic String[] selectImports(AnnotationMetadata annotationMetadata) {return new String[]{Stu2.class.getName()};}
}

通过字符串数组的方式返回配置类的全限定名。

3、将MyImportSelector加入配置类MyImport

@Configuration
@Import({Stu1.class,MyImportSelector.class})
public class MyImport {
}

4、测试类：

public class App 
{public static void main( String[] args ){ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");String[] beanDefinitionNames = context.getBeanDefinitionNames();for (String name : beanDefinitionNames) {System.out.println(name + ": " + context.getBean(name));}System.out.println("++++++++++++++");MyImport myImport = (MyImport) context.getBean("myImport");System.out.println(myImport);Object bean1 = context.getBean("impotTest.pojo.Stu1");System.out.println(bean1);Object bean2 = context.getBean("impotTest.pojo.Stu2");System.out.println(bean2);System.out.println("+++++");}
}

运行结果：

org.springframework.context.annotation.internalConfigurationAnnotationProcessor: org.springframework.context.annotation.ConfigurationClassPostProcessor@4b0b0854
org.springframework.context.annotation.internalAutowiredAnnotationProcessor: org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor@19bb07ed
org.springframework.context.annotation.internalCommonAnnotationProcessor: org.springframework.context.annotation.CommonAnnotationBeanPostProcessor@10e41621
org.springframework.context.event.internalEventListenerProcessor: org.springframework.context.event.EventListenerMethodProcessor@353d0772
org.springframework.context.event.internalEventListenerFactory: org.springframework.context.event.DefaultEventListenerFactory@2667f029
org.springframework.aop.config.internalAutoProxyCreator: proxyTargetClass=false; optimize=false; opaque=false; exposeProxy=false; frozen=false
myImport: impotTest.pojo.imports.MyImport$$EnhancerBySpringCGLIB$$49a6e31e@e056f20
impotTest.pojo.Stu1: impotTest.pojo.Stu1@67a20f67
impotTest.pojo.Stu2: impotTest.pojo.Stu2@57c758ac
++++++++++++++
impotTest.pojo.imports.MyImport$$EnhancerBySpringCGLIB$$49a6e31e@e056f20
impotTest.pojo.Stu1@67a20f67
impotTest.pojo.Stu2@57c758ac
+++++

实现ImportBeanDefinitionRegistrar的方式

1、新建类Stu3：

package impotTest.pojo;public class Stu3 {
}

2、新建MyImportBeanDefinitionRegistrar实现ImportBeanDefinitionRegistrar

package impotTest.pojo.imports;
...public class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {@Overridepublic void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {registry.registerBeanDefinition("stu3", new RootBeanDefinition(Stu3.class));}
}

registerBeanDefinition方法第一个参数可以指定注入容器的bean名称。本例中指定bean名称为 “stu3”

3、将MyImportBeanDefinitionRegistrar加入配置类MyImport

@Configuration
@Import({Stu1.class,MyImportSelector.class,MyImportBeanDefinitionRegistrar.class})
public class MyImport {
}

4、测试类：

public class App 
{public static void main( String[] args ){ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");String[] beanDefinitionNames = context.getBeanDefinitionNames();for (String name : beanDefinitionNames) {System.out.println(name + ": " + context.getBean(name));}System.out.println("++++++++++++++");MyImport myImport = (MyImport) context.getBean("myImport");System.out.println(myImport);Object bean1 = context.getBean("impotTest.pojo.Stu1");System.out.println(bean1);Object bean2 = context.getBean("impotTest.pojo.Stu2");System.out.println(bean2);Object bean3 = context.getBean("stu3");System.out.println(bean3);System.out.println("+++++");}
}

运行结果：

org.springframework.context.annotation.internalConfigurationAnnotationProcessor: org.springframework.context.annotation.ConfigurationClassPostProcessor@67a20f67
org.springframework.context.annotation.internalAutowiredAnnotationProcessor: org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor@57c758ac
org.springframework.context.annotation.internalCommonAnnotationProcessor: org.springframework.context.annotation.CommonAnnotationBeanPostProcessor@a9cd3b1
org.springframework.context.event.internalEventListenerProcessor: org.springframework.context.event.EventListenerMethodProcessor@13e39c73
org.springframework.context.event.internalEventListenerFactory: org.springframework.context.event.DefaultEventListenerFactory@64cd705f
org.springframework.aop.config.internalAutoProxyCreator: proxyTargetClass=false; optimize=false; opaque=false; exposeProxy=false; frozen=false
myImport: impotTest.pojo.imports.MyImport$$EnhancerBySpringCGLIB$$649a2b62@2667f029
impotTest.pojo.Stu1: impotTest.pojo.Stu1@9225652
impotTest.pojo.Stu2: impotTest.pojo.Stu2@654f0d9c
stu3: impotTest.pojo.Stu3@6a400542
++++++++++++++
impotTest.pojo.imports.MyImport$$EnhancerBySpringCGLIB$$649a2b62@2667f029
impotTest.pojo.Stu1@9225652
impotTest.pojo.Stu2@654f0d9c
impotTest.pojo.Stu3@6a400542
+++++

小结

spring容器注入三种方式：

1. 通过xml配置、注解
2. 通过 @Configuration 与 @Bean 这两个注解配合
3. @Import 方式注入