Spring 框架中的@import注解

@import注解是Spring基于java注解配置的主要组成部分，import注解提供了@Bean注解的功能，同时还有原来组织多个分散的@Configuration的功能。

import注解可以引入其他的configuration

example code :

public interface TestService {
    void test();
}

@Configuration
@Import({ConfigB.class})     //@Import的优先于本身的的类定义加载
public class ConfigA {
    @Bean
    @ConditionalOnMissingBean
    public TestService getTestService() {
        return new TestServiceA();
    }
}

@Configuration
public class ConfigB {
    @Bean
    @ConditionalOnMissingBean
    public TestService getTestServiceB() {
        return new TestServiceB();
    }
}

场景类代码:

public static void main(String[] args) {
    ApplicationContext applicationContext = new AnnotationConfigApplicationContext(ConfigA.class);
    TestService testService = applicationContext.getBean(TestService.class);
    testService.test();
    //generate TestServiceB
}

import 注解也可以直接初始化其他类的Bean

@Configuration
@Import({TestServiceC.class})     //@Import的优先于本身的的类定义加载
public class ConfigA {
    @Bean
    @ConditionalOnMissingBean
    public TestService getTestService() {
        return new TestServiceA();
    }
}

场景类保持不变，此时TestService实例会变成TestServiceC 的实例。

个性化加载，指定实现ImportSelector

实现importSelector接口可实现个性化加载，下面是示例代码

public class MyimportSelector implements ImportSelector {
    /**
     * Select and return the names of which class(es) should be imported based on the {@link AnnotationMetadata} of the
     * importing @{@link Configuration} class.
     *
     * @param importingClassMetadata
     */
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        return new String[]{"com.mirsery.test.webtest.anno.TestServiceA"};//    可以直接返回实体或者对应的config配置类
    }
}

基于AnnotationMetadata的参数实现动态加载类示例:

@Retention(RetentionPolicy.RUNTIME)
@Documented
@Target(ElementType.TYPE)
@Import(My1importSelector.class)
public @interface EnableTestService {
    String name();
}

public class My1importSelector implements ImportSelector {
    /**
     * Select and return the names of which class(es) should be imported based on the {@link AnnotationMetadata} of the
     * importing @{@link Configuration} class.
     *
     * @param importingClassMetadata
     */
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        Map<String , Object> map = importingClassMetadata.getAnnotationAttributes(EnableTestService.class.getName(), true);
        String name = (String) map.get("name");
        if (Objects.equals(name, "B")) {//
            return new String[]{"com.mirsery.test.webtest.anno.ConfigB"};
        }
        return new String[0];
    }
}


场景类直接使用标注
@EnableTestService(name="B")

实现ImportBeanDefinitionRegistrar 接口个性化加载

和importSelector 类型，想要重新定义Bean，例如动态注入属性改变Bean的类型和Scope等等就需要通过实现ImportBeanDefinitionRegister的类实现,下面是示例代码:
//TODO