模拟实现ComponentScan

最新推荐文章于 2025-04-02 22:54:41 发布

a11157

最新推荐文章于 2025-04-02 22:54:41 发布

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文章标签： java 开发语言

本文链接：https://blog.youkuaiyun.com/a11157/article/details/126344802

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本文档详细介绍了如何模拟实现对Bean1类中使用到的@ComponentScan注解进行扫描，包括自定义BeanFactoryPostProcessor，Bean1的结构，包的组织以及测试和最终的成功结果。

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实现对Bean1类的@ComponentScan注解的扫描

自定义实现一个BeanFactoryPostProcessor

//模拟实现ComponentScan
public class ComponentScanProcessor implements BeanFactoryPostProcessor {
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {
        DefaultListableBeanFactory beanFactory = (DefaultListableBeanFactory) configurableListableBeanFactory;

        SimpleMetadataReaderFactory readerFactory = new SimpleMetadataReaderFactory();
        BeanNameGenerator nameGenerator = new AnnotationBeanNameGenerator();
        //用AnnotationUtils查找此类上有没有ComponentScan注解
        ComponentScan componentScan = AnnotationUtils.findAnnotation(Bean1.class, ComponentScan.class);
        //不为空，有注解
        if (componentScan != null) {
            String[] packages = componentScan.basePackages();
            for (String path : packages) {
                //包名转换为路径名
                //com.ghc.springlearning---->classpath*:com/ghc/springlearning/../*.class
                String s = "classpath*:" + path.replace('.', '/') + "/**/*.class";
                try {
                    Resource[] resources = new PathMatchingResourcePatternResolver().getResources(s);
                    for (Resource resource : resources) {
                        MetadataReader reader = readerFactory.getMetadataReader(resource);
                        AnnotationMetadata annotationMetadata = reader.getAnnotationMetadata();
                        if (annotationMetadata.hasAnnotation(Component.class.getName())
                                || annotationMetadata.hasMetaAnnotation(Component.class.getName())) {
                            AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder
                                    .genericBeanDefinition(reader.getClassMetadata().getClassName())
                                    .getBeanDefinition();
                            String beanName = nameGenerator.generateBeanName(beanDefinition, beanFactory);
                            beanFactory.registerBeanDefinition(beanName, beanDefinition);
                        }
                    }
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }

            }
        }
    }
}

Bean1结构

@ComponentScan({"com.ghc.springlearning.MyPostProcessors.components"})
@Configuration
public class Bean1 {

}

包结构

测试：

public class Test {
    public static void main(String[] args) {
        GenericApplicationContext context = new GenericApplicationContext();
        context.registerBean("bean1",Bean1.class);
        context.registerBean(ComponentScanProcessor.class);
        context.refresh();
        for (String name : context.getBeanDefinitionNames()) {
            System.out.println(name);
        }
    }
}