spring源码分析——BeanPostProcessor接口

　　BeanPostProcessor是处理bean的后置接口，beanDefinitionMaps中的BeanDefinition实例化完成后，完成populateBean，属性设置，完成

初始化后，这个接口支持对bean做自定义的操作。

一：BeanPostProcessor的使用

定义一个测试用的model对象，name属性默认为hello

public class BeanDemo {

	private String name = "hello";

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	@Override
	public String toString() {
		final StringBuffer sb = new StringBuffer("BeanDemo{");
		sb.append("name='").append(name).append('\'');
		sb.append('}');
		return sb.toString();
	}
}

自定义一个MyBeanPostProcessor类，实现BeanPostProcessor接口

@Service
public class MyBeanPostProcessor implements BeanPostProcessor {

	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		return null;
	}

	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		if(beanName.equals("beanDemo")){
			BeanDemo beanDemo = (BeanDemo)bean;
			beanDemo.setName("kitty");
			return beanDemo;
		}
		return bean;
	}
}

从运行结果看，spring中维护的beanName为beanDemo的对象，name属性为ketty

二：看看源码怎么实现的

1：实例化并且注册到beanPostProcessors集合中

主要的实例化逻辑在这个接口，这个接口的作用就是把所有实现BeanPostProcessor接口的类实例化，然后注册到 beanPostProcessors这个缓存中

public static void registerBeanPostProcessors(
			ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

		// 获取所有实现接口BeanPostProcessor的beanName
		String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

		// Register BeanPostProcessorChecker that logs an info message when
		// a bean is created during BeanPostProcessor instantiation, i.e. when
		// a bean is not eligible for getting processed by all BeanPostProcessors.
		int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
		beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

		// Separate between BeanPostProcessors that implement PriorityOrdered,
		// Ordered, and the rest.
		/**
		 * 把实现PriorityOrdered 和 Ordered 和 其他的处理器分开
		 */
		List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
		List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
		List<String> orderedPostProcessorNames = new ArrayList<>();
		List<String> nonOrderedPostProcessorNames = new ArrayList<>();
		/**
		 * 1：遍历集合postProcessorNames
		 * 2：判断类型，如果是PriorityOrdered，则实例化对象放入priorityOrderedPostProcessors集合，
		 * Ordered 则放入orderedPostProcessorNames集合，其他的放入nonOrderedPostProcessorNames集合
 		 */
		for (String ppName : postProcessorNames) {
			if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
				BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
				priorityOrderedPostProcessors.add(pp);
				if (pp instanceof MergedBeanDefinitionPostProcessor) {
					internalPostProcessors.add(pp);
				}
			}
			else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
				orderedPostProcessorNames.add(ppName);
			}
			else {
				nonOrderedPostProcessorNames.add(ppName);
			}
		}

		// First, register the BeanPostProcessors that implement PriorityOrdered.
		// 首先对priorityOrderedPostProcessors集合中实例对象排序，然后注册，放入beanFactory中缓存下来
		sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
		registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

		// Next, register the BeanPostProcessors that implement Ordered.
		// 然后再实例化实现Ordered接口的对象，完成注册
		List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
		for (String ppName : orderedPostProcessorNames) {
			BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
			orderedPostProcessors.add(pp);
			if (pp instanceof MergedBeanDefinitionPostProcessor) {
				internalPostProcessors.add(pp);
			}
		}
		sortPostProcessors(orderedPostProcessors, beanFactory);
		registerBeanPostProcessors(beanFactory, orderedPostProcessors);

		// Now, register all regular BeanPostProcessors.
		// 最后实例化什么都没有实现的，完成实例化并注册
		List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
		for (String ppName : nonOrderedPostProcessorNames) {
			BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
			nonOrderedPostProcessors.add(pp);
			if (pp instanceof MergedBeanDefinitionPostProcessor) {
				internalPostProcessors.add(pp);
			}
		}
		registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

		// Finally, re-register all internal BeanPostProcessors.
		// 最后再次注册内部postProcessor
		sortPostProcessors(internalPostProcessors, beanFactory);
		registerBeanPostProcessors(beanFactory, internalPostProcessors);

		// Re-register post-processor for detecting inner beans as ApplicationListeners,
		// moving it to the end of the processor chain (for picking up proxies etc).
		beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
	}