背景

@Configuration 注解的类会被spring自动的扫描注入为Bean,如果想自己定义一个注解实现相同的功能如何来实现

ImportBeanDefinitionRegistrar

熟悉spring源码的同学应该知道，注册bean实际上就是注册beandefinition
这个类刚好有接口可以实现

default void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry,
			BeanNameGenerator importBeanNameGenerator) {

		registerBeanDefinitions(importingClassMetadata, registry);
	}

1.定义注解

此注解在类上定义

@Documented
@Inherited
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER})
public @interface Ma {
}

2.启动注解

spring启动类上注解
引入ImportBeanDefinitionRegistrar实现

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(MapperAutoConfigureRegistrar.class)
public @interface MapperAutoCon {
}

3.实现接口

public class MapperAutoConfigureRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware {

    private ResourceLoader resourceLoader;

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        MapperBeanDefinitionScanner scanner = new MapperBeanDefinitionScanner(registry, false);
        scanner.setResourceLoader(resourceLoader);
        scanner.registerFilters();
        //这里增加对Ma注解类的扫描
        scanner.addIncludeFilter(new AnnotationTypeFilter(Ma.class));
        //测试直接写死，可改成要scan的目录
        scanner.doScan("com.si");
    }

    @Override
    public void setResourceLoader(ResourceLoader resourceLoader) {
        this.resourceLoader = resourceLoader;
    }
}

4.扫描器

public class MapperBeanDefinitionScanner extends ClassPathBeanDefinitionScanner {

    public MapperBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters) {
        super(registry, useDefaultFilters);
    }

    protected void registerFilters() {
        addIncludeFilter(new AnnotationTypeFilter(Ma.class));
    }

    @Override
    protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
        return super.doScan(basePackages);
    }
}

5.使用Bean

@Configuration
public class Us {

    //这里引入@Ma注解的
    @Autowired
    UserMapper userMapper;

    @Autowired
    public void init(){
        userMapper.say();
    }
}

6.使用注解

@Ma
public class UserMapper {

    public void say(){
        System.out.println("hello ");
    }
}

7.启动类

@SpringBootApplication
//启动类中引入这个注解
@MapperAutoCon
public class MapperAutoConfigureRegistrarTest {

    public static void main(String[] args) {
        SpringApplication.run(MapperAutoConfigureRegistrarTest.class,args);
    }


}

总结

实现了自定义注解功能，这个注解可以用作jar在其它项目中使用，对于造轮子来说还是可以的