本节内容 & 思考题

实现 Spring 中包扫描 @Component 注解

<context:component-scan base-package="com.dist.ars.aop.test"/>

实现注解版实例工厂（@Configuration + @Bean 注解实现）

猜猜 @ComponentScan 和 xml 中的包扫描，Spring 是怎样实现的呢？

实现配置文件包扫描

1、@Component 注解

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface Component {

    String value() default "";
}

2、修改 json 文件格式

{
  "beans": [
    {
      "name": "appleFactory",
      "className": "cn.x5456.summer.AppleFactory"
    },
    {
      "name": "initAnnotationBeanPostProcessor",
      "className": "cn.x5456.summer.InitAnnotationBeanPostProcessor"
    }
  ],
  "componentScanPackages": [
    "cn.x5456.summer"
  ]
}

3、修改 JsonBeanFactoryImpl

public class JsonBeanFactoryImpl extends ListableBeanFactoryImpl {

    public JsonBeanFactoryImpl(String filePath) {
        this.loadBeanDefinitions(filePath);
    }

    public JsonBeanFactoryImpl(String filePath, BeanFactory parentBeanFactory) {
        super(parentBeanFactory);
        this.loadBeanDefinitions(filePath);
    }

    private void loadBeanDefinitions(String filePath) {
        String json = FileUtil.readUtf8String(filePath);
        Map<String, Object> configMap = JsonUtils.toMap(json, String.class, Object.class);

        List<Map<String, String>> beanDefinitionList = (List<Map<String, String>>) configMap.get("beans");
        if (ObjectUtil.isNotEmpty(beanDefinitionList)) {
            for (Map<String, String> map : beanDefinitionList) {
                BeanDefinition bd = BeanUtil.mapToBeanIgnoreCase(map, DefaultBeanDefinition.class, true);
                super.registerBeanDefinition(bd.getName(), bd);
            }
        }

        // 读取包扫描路径
        List<String> scanPackageNames = (List<String>) configMap.get("componentScanPackages");
        if (ObjectUtil.isNotEmpty(scanPackageNames)) {
            for (String packageName : scanPackageNames) {
                Set<Class<?>> classes = ClassUtil.scanPackage(packageName);
                for (Class<?> clazz : classes) {
                    // 判断是否具有 @Component 注解，并且本身不是注解
                    Component component = AnnotationUtil.getAnnotation(clazz, Component.class);
                    if (ObjectUtil.isNotNull(component) && !clazz.isAnnotation()) {
                        DefaultBeanDefinition bd = new DefaultBeanDefinition();
    
                        String beanName = StrUtil.isNotBlank(component.value()) ? component.value() : StrUtil.lowerFirst(clazz.getSimpleName());
                        bd.setName(beanName);
                        bd.setClassName(clazz.getName());
    
                        // TODO: 2020/4/18 参数列表
    
                        super.registerBeanDefinition(beanName, bd);
                    }
                }
            }
        }

        // 向 beanPostProcessors 中添加后置处理器
        for (BeanPostProcessor beanPostProcessor : super.getBeansOfType(BeanPostProcessor.class).values()) {
            super.addBeanPostProcessor(beanPostProcessor);
        }
    }
}

使用 BeanDefinitionRegistryPostProcessor 实现对配置类中 @Bean 注解的扫描

1、@Bean

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface Bean {

    /**
     * 组件名称
     */
    String value() default "";

    /**
     * 初始化方法
     */
    String initMethod() default "";

    /**
     * 销毁方法
     */
    String destroyMethod() default "";

}

2、新增 BeanDefinitionRegistry#registerBeanDefinition

public interface BeanDefinitionRegistry {

    /**
     * 注册 bd 到 bf
     */
    void registerBeanDefinition(String name, BeanDefinition beanDefinition);

    /**
     * 根据 bdName 获取 bd
     */
    BeanDefinition getBeanDefinition(String name);
}

3、ConfigurationClassPostProcessor

public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPostProcessor {

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
        ListableBeanFactory bf = (ListableBeanFactory) registry;

        for (String bdName : bf.getBeanDefinitionNames()) {
            BeanDefinition classBeanDefinition = registry.getBeanDefinition(bdName);
            String className = classBeanDefinition.getClassName();
            Class<?> clazz = ReflectUtils.getType(className);

            // 找到类上携带 @Configuration 的
            Configuration configuration = AnnotationUtil.getAnnotation(clazz, Configuration.class);
            if (ObjectUtil.isNotEmpty(configuration)) {
                // 循环找方法中包含 @Bean 注解的
                for (Method method : clazz.getMethods()) {
                    if (method.isAnnotationPresent(Bean.class)) {
                        BeanDefinition bdDef = new DefaultBeanDefinition();

                        Bean bean = method.getAnnotation(Bean.class);
                        String beanName = ObjectUtil.isNotEmpty(bean.value()) ? bean.value() : method.getName();

                        bdDef.setName(beanName);
                        bdDef.setFactoryBean(classBeanDefinition.getName());
                        bdDef.setFactoryMethod(method.getName());
                        bdDef.setInitMethod(bean.initMethod());
                        bdDef.setDestroyMethod(bean.destroyMethod());

                        // TODO: 2020/4/18 属性列表

                        registry.registerBeanDefinition(beanName, bdDef);
                    }
                }
            }
        }
    }
}