002-InstantiationAwareBeanPostProcessor

1.目的

以前也稍微了解spring的源码，最近在研究研究，记录一下心得。
今天就针对spring中InstantiationAwareBeanPostProcessor的理解进行加深一下。

2.InstantiationAwareBeanPostProcessor是什么？

spring中基础对象都是bean! 那么InstantiationAwareBeanPostProcessor也是一个bean，只不过多了一层关系，实现InstantiationAwareBeanPostProcessor接口。
这个接口InstantiationAwareBeanPostProcessor是BeanPostProcessor扩展的子接口

3.InstantiationAwareBeanPostProcessor，BeanPostProcessor有什么区别？

BeanPostProcessor：有两个方法postProcessBeforeInitialization方法和postProcessAfterInitialization（）。
在bean初始化的时候，也就是Spring激活bean的init-method方法的前后，会调用BeanPostProcessor的postProcessBeforeInitialization方法和postProcessAfterInitialization。

InstantiationAwareBeanPostProcessor：有三个方法
postProcessBeforeInstantiation（），postProcessAfterInstantiation（返回值boolean），postProcessPropertyValues（）
1.在bean实例化过程（生成实例对象）前后调用。
涉及这两个方法 postProcessBeforeInstantiation（），postProcessAfterInstantiation（父接口中的方法）
2.当然也在初始化（setter注入，init方法）的过程中的setter注入这一步之前调用。涉及这两个方法 postProcessAfterInstantiation 返回值boolean,postProcessPropertyValues（）

4.InstantiationAwareBeanPostProcessor如何被识别出来的？

因为InstantiationAwareBeanPostProcessor的父接口是beanPostProcessor，所以被设别的地方同beanPostProcessor地方一样

在AbstractApplicationContext方法中registerBeanPostProcessors()
代码行数：
版本：spring-core-3.0.0.RELEASE-sources.jar
方法中：AbstractApplicationContext.registerBeanPostProcessors（） 401行

        registerBeanPostProcessors(beanFactory);

    protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

5.InstantiationAwareBeanPostProcessor中的方法是何时被调用？

5.1postProcessBeforeInstantiation（），postProcessAfterInstantiation(父接口中方法)何时被调用？

5.1.1在createBean方法里面有个resolveBeforeInstantiation方法

@Override
    protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
    // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
            Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
            if (bean != null) {
                return bean;
            }
    //省略....
    Object beanInstance = doCreateBean(beanName, mbdToUse, args);
    return beanInstance;

    }

上面代码里面看到,在执行doCreateBean之前有resolveBeforeInstantiation方法；doCreateBean是创建bean的方法；
resolveBeforeInstantiation是判断执行InstantiationAwareBeanPostProcessor.postProcessBeforeInstantiation的接方法实现;

5.1.2

执行 postProcessBeforeInstantiation方法的时机

/**
     * Apply before-instantiation post-processors, resolving whether there is a
     * before-instantiation shortcut for the specified bean.
     * @param beanName the name of the bean
     * @param mbd the bean definition for the bean
     * @return the shortcut-determined bean instance, or {@code null} if none
     */
    protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
        Object bean = null;
        //如果beforeInstantiationResolved还没有设置或者是false（说明还没有需要在实例化前执行的操作）
        if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
            // 判断是否有注册过InstantiationAwareBeanPostProcessor类型的bean
            if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
                Class<?> targetType = determineTargetType(beanName, mbd);
                if (targetType != null) {
                    //执行
                    bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
                    if (bean != null) {
                        bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
                    }
                }
            }
            mbd.beforeInstantiationResolved = (bean != null);
        }
        return bean;
    }

protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
        for (BeanPostProcessor bp : getBeanPostProcessors()) {
            if (bp instanceof InstantiationAwareBeanPostProcessor) {
                InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                Object result = ibp.postProcessBeforeInstantiation(beanClass, beanName);
                //只要有一个result不为null；后面的所有 后置处理器的方法就不执行了，直接返回(所以执行顺序很重要)
                if (result != null) {
                    return result;
                }
            }
        }
        return null;
    }

5.1.3执行postProcessAfterInstantiation(父接口中方法)的时机

@Override
    public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
            throws BeansException {

        Object result = existingBean;
        for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
            result = beanProcessor.postProcessAfterInitialization(result, beanName);
            //如果返回null；后面的所有 后置处理器的方法就不执行，直接返回(所以执行顺序很重要)
            if (result == null) {
                return result;
            }
        }
        return result;
    }

5.2postProcessAfterInstantiation（返回值boolean）postProcessPropertyValues（）何时被调用？

5.2.1执行postProcessAfterInstantiation（返回值boolean）的时机.

AbstractAutowireCapableBeanFactory.populateBean()

    if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
            for (BeanPostProcessor bp : getBeanPostProcessors()) {
                if (bp instanceof InstantiationAwareBeanPostProcessor) {
                    InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                    if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
                        continueWithPropertyPopulation = false;
                        break;
                    }
                }
            }
        }

5.2.2执行postProcessPropertyValues的时机