Spring @ Import explain and use

In the application, we will inject a lot of class to the IOC, it is sometimes not the IOC injected into the container of a class, but not in use when the need to get the class corresponding to the bean, then you need to use @Import comment.

A. @Import use

Introduction 1.1 @Import

• Directly into the class
• Manner by introducing configuration class, the configuration at this time or need to achieve ImportSelector ImportBeanDefinitionRegistrar
  NOTE: @Import import components, id for whole class name component

1.2 @Import use

1.2.1 define several Bean

At this time, and is not injected into the vessel IOC

@Data
public class SuperMan {
    private String name;
    private Integer age;
}
---------
@Data
public class Man {
    private String userName;
    private String email;
}
--------
@Data
public class Bule {
    private Integer code;
}

1.2.2 @Import injection

@Configuration
@Import({SuperMan.class, SuperSelector.class,MyDefinitionRegistrar.class})
public class MainConfig {
}

MyDefinitionRegistrar, SuperSelector is by way of the configuration file

public class MyDefinitionRegistrar implements ImportBeanDefinitionRegistrar {
    @Override
    public void registerBeanDefinitions(AnnotationMetadata annotationMetadata,
                                        BeanDefinitionRegistry beanDefinitionRegistry) {
        boolean beanDefinition = beanDefinitionRegistry.containsBeanDefinition("com.javayh.api.bean.SuperMan");
        if(beanDefinition){
            RootBeanDefinition rootBeanDefinition = new RootBeanDefinition(Bule.class);
            beanDefinitionRegistry.registerBeanDefinition("bule",rootBeanDefinition);
//            beanDefinitionRegistry.removeBeanDefinition("com.javayh.api.bean.Man");
        }

    }
}

public class SuperSelector implements ImportSelector {
    @Override
    public String[] selectImports(AnnotationMetadata annotationMetadata) {

        return new String[]{
                "com.javayh.api.bean.Man"
        };
    }
}

1.3 verification

public class TestMain {
    AnnotationConfigApplicationContext applicationContext =
            new AnnotationConfigApplicationContext(MainConfig.class);

    @Test
    public void testImport(){
        printBeans(applicationContext);
        SuperMan bean = applicationContext.getBean(SuperMan.class);
        Man man = applicationContext.getBean(Man.class);
        Bule bule = applicationContext.getBean(Bule.class);
        System.out.println(bean);
        System.out.println(man);
        System.out.println(bule);
    }


    private void printBeans(AnnotationConfigApplicationContext applicationContext){
        String[] definitionNames = applicationContext.getBeanDefinitionNames();
        for (String name : definitionNames) {
            System.out.println(name);
        }
    }
}

FIG follows: when we have used injected into the IOC

which we can @Import commented, or open code is commented, running

If you open the code commented out, you will find the errors below occur!

II. Extended

@Import in many SpringBoot underlying application, as shown below

Next we look at the source code

public class AutoConfigurationImportSelector 
	implements DeferredImportSelector, 
	BeanClassLoaderAware, ResourceLoaderAware, 
	BeanFactoryAware, EnvironmentAware, Ordered {
 
}

Found implements many interfaces, including DeferredImportSelectorimport selectors, but DeferredImportSelectoralso inherited theImportSelector

public interface ImportSelector {
    String[] selectImports(AnnotationMetadata var1);
}
 

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