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ClassPathBeanDefinitionScanner 自定义注解扫描器 ​

自定义注解 ​

java
// 自定义注解
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface MyComponent {
    String value() default "";
}

// 类上添加上面的自定义注解
@MyComponent
public class UserComponent {
}

在 BeanDefinitionRegistryPostProcessor 中使用扫描器扫描 ​

扫描指定目录下所有添加了自定义的 @MyComponent 注解的类，并在后面的流程中为其创建 BeanDefinition 对象，最终初始化到 Spring 容器中。

ClassPathBeanDefinitionScanner 继承了 ClassPathScanningCandidateComponentProvider 类。

ClassPathBeanDefinitionScanner 应用还有 MyBatis 中的 ClassPathMapperScanner 继承了 ClassPathBeanDefinitionScanner。

ClassPathScanningCandidateComponentProvider 的应用还有 @ServletComponentScan 注解，扫描类中包含 @WebServlet, @WebFilter, @WebListener 注解。

java
package com.github.mengweijin.mybatisplus.demo.ClassPathBeanDefinitionScanner.bean;

import com.github.mengweijin.mybatisplus.demo.ClassPathBeanDefinitionScanner.MyComponent.MyComponent;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.context.annotation.ClassPathBeanDefinitionScanner;
import org.springframework.core.type.filter.AnnotationTypeFilter;
import org.springframework.stereotype.Component;

@Component
public class MyBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {
    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        //根据BeanDefinitionRegistry对象获创建注解扫描器(Spring源码实现也是通过new 的方式)
        //ClassPathBeanDefinitionScanner类就是自定义注解的支撑
        ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(registry);
        // 添加自定义注解到注册器中（可以添加多个实现了 TypeFilter 的过滤器）
        scanner.addIncludeFilter(new AnnotationTypeFilter(MyComponent.class));
        // 指定注解扫描器的包路径(字符串)
        scanner.scan("com.github.mengweijin.mybatisplus.demo.ClassPathBeanDefinitionScanner.MyComponent");
    }

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
    }
}

测试 ​

java
package com.github.mengweijin.mybatisplus.demo.ClassPathBeanDefinitionScanner;

import com.github.mengweijin.mybatisplus.demo.ClassPathBeanDefinitionScanner.MyComponent.UserComponent;
import org.junit.jupiter.api.Assertions;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

@SpringBootApplication(scanBasePackages = "com.github.mengweijin.mybatisplus.demo.ClassPathBeanDefinitionScanner.bean")
public class MyComponentTest {

    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(MyComponentTest.class, args);
        UserComponent bean = context.getBean(UserComponent.class);
        System.out.println(bean);
        Assertions.assertNotNull(bean);

        context.close();
    }
}