Spring覆盖容器中Bean的注解如何实现@OverrideBean

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * 覆盖Spring容器中的Bean
 *
 * @author shanhy
 * @date 2021/4/25 13:40
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface OverrideBean {

    /**
     * 需要替换的 Bean 的名称
     *
     * @return
     */
    String value();
    
}

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.config.BeanDefinitionHolder;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.beans.factory.support.GenericBeanDefinition;
import org.springframework.boot.autoconfigure.AutoConfigurationPackages;
import org.springframework.context.annotation.ClassPathBeanDefinitionScanner;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.type.filter.AnnotationTypeFilter;
import org.springframework.util.StringUtils;

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.Set;

/**
 * 重写Bean的配置类
 *
 * @author shanhy
 * @date 2021/4/25 13:41
 */
@Configuration
public class OverrideBeanConfiguration implements BeanDefinitionRegistryPostProcessor, BeanFactoryAware {

    private static final Logger log = LoggerFactory.getLogger(OverrideBeanConfiguration.class);

    private BeanFactory beanFactory;

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        log.debug("searching for classes annotated with @OverrideBean");

        // 自定义 Scanner 扫描 classpath 下的指定注解
        ClassPathOverrideBeanAnnotationScanner scanner = new ClassPathOverrideBeanAnnotationScanner(registry);
        try {
            // 获取包路径
            List<String> packages = AutoConfigurationPackages.get(this.beanFactory);

            if (log.isDebugEnabled()) {
                for (String p : packages) {
                    log.debug("Using auto-configuration base package: {}", p);
                }
            }

            // 扫描所有加载的包
            scanner.doScan(StringUtils.toStringArray(packages));
        } catch (IllegalStateException ex) {
            log.debug("could not determine auto-configuration package, automatic OverrideBean scanning disabled.", ex);
        }
    }

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

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        this.beanFactory = beanFactory;
    }

    private static class ClassPathOverrideBeanAnnotationScanner extends ClassPathBeanDefinitionScanner {

        ClassPathOverrideBeanAnnotationScanner(BeanDefinitionRegistry registry) {
            super(registry, false);
            // 设置过滤器。仅扫描 @OverrideBean
            addIncludeFilter(new AnnotationTypeFilter(OverrideBean.class));
        }

        @Override
        public Set<BeanDefinitionHolder> doScan(String... basePackages) {
            List<String> overrideClassNames = new ArrayList<>();
            // 扫描全部 package 下 annotationClass 指定的 Bean
            Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);

            GenericBeanDefinition definition;
            for (BeanDefinitionHolder holder : beanDefinitions) {
                definition = (GenericBeanDefinition) holder.getBeanDefinition();

                // 获取类名，并创建 Class 对象
                String className = definition.getBeanClassName();
                Class<?> clazz = classNameToClass(className);

                // 解析注解上的 value
                OverrideBean annotation = Objects.requireNonNull(clazz).getAnnotation(OverrideBean.class);
                if (annotation == null || annotation.value().length() == 0) {
                    continue;
                }

                // 使用当前加载的 @OverrideBean 指定的 Bean 替换 value 里指定名称的 Bean
                if (Objects.requireNonNull(getRegistry()).containsBeanDefinition(annotation.value())) {
                    getRegistry().removeBeanDefinition(annotation.value());
                    getRegistry().registerBeanDefinition(annotation.value(), definition);
                    overrideClassNames.add(clazz.getName());
                }
            }
            log.info("found override beans: " + overrideClassNames);

            return beanDefinitions;
        }

        // 反射通过 class 名称获取 Class 对象
        private Class<?> classNameToClass(String className) {
            try {
                return Class.forName(className);
            } catch (ClassNotFoundException e) {
                log.error("create instance failed.", e);
            }
            return null;
        }
    }

}