依赖查找

• 双亲委派机制
• • HierarchicalBeanFactory
  • BeanFactoryUtils

• 什么是双亲委派机制？

  先找“老子”，再找“小子”。

双亲委派机制

HierarchicalBeanFactory

HierarchicalBeanFactory是层次性BeanFactory。

• 查看HierarchicalBeanFactory继承树

• 获取ConfigurableListableBeanFactory

ConfigurableListableBeanFactory beanFactory = applicationContext.getBeanFactory();
// 设置父BeanFactory
// 调用createParentBeanFactory（）方法是加载另一个BeanFactory，
beanFactory.setParentBeanFactory(createParentBeanFactory());

 private static HierarchicalBeanFactory createParentBeanFactory() {
        DefaultListableBeanFactory defaultListableBeanFactory = new DefaultListableBeanFactory();
        XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(defaultListableBeanFactory);
        int i = reader.loadBeanDefinitions("classpath:/META-INF/dependency-looKup-context.xml");
        return defaultListableBeanFactory;
}

• 查看当前BeanFactory是否含有Bean

//containsLocalBean(String)
public static void displayLocalBean(HierarchicalBeanFactory beanFactory, String beanName) {
        System.out.printf("当前 BeanFactory[%s] 是否包含bean[name : %s]   包含了:[%s] \n", beanFactory, beanName, beanFactory.containsLocalBean(beanName));
}

这些只能查看当前的BeanFactory，并不能查看前面设置的父BeanFactory，需要改进：

• 子父全查

    private static boolean containsBean(HierarchicalBeanFactory beanFactory, String beanName) {
        BeanFactory parentBeanFactory = beanFactory.getParentBeanFactory();
        if (parentBeanFactory instanceof HierarchicalBeanFactory) {
            HierarchicalBeanFactory cast = (HierarchicalBeanFactory) parentBeanFactory;
            if (containsBean(cast, beanName)) {
                return true;
            }
        }
        return beanFactory.containsLocalBean(beanName);
    }

综上所述，这个双亲委派机制可以使用BeanFactoryUtils#beanNamesForTypeIncludingAncestors（包含祖先的类型的 bean 名称）获取到 “父子” BeanFactory中的Bean；

BeanFactoryUtils

	public static String[] beanNamesForTypeIncludingAncestors(ListableBeanFactory lbf, Class<?> type) {
		Assert.notNull(lbf, "ListableBeanFactory must not be null");
		String[] result = lbf.getBeanNamesForType(type);
		if (lbf instanceof HierarchicalBeanFactory) {
			HierarchicalBeanFactory hbf = (HierarchicalBeanFactory) lbf;
			if (hbf.getParentBeanFactory() instanceof ListableBeanFactory) {
				String[] parentResult = beanNamesForTypeIncludingAncestors(
						(ListableBeanFactory) hbf.getParentBeanFactory(), type);
				result = mergeNamesWithParent(result, parentResult, hbf);
			}
		}
		return result;
	}