Spring中的InstantiationAwareBeanPostProcessor和BeanPostProcessor

InstantiationAwareBeanPostProcessor接口继承了BeanPostProcessor。

BeanPostProcessor接口中有2个方法

1.Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;

2.Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;

InstantiationAwareBeanPostProcessor中除了上述的两个方法外还有本身接口的方法

1.Object postProcessBeforeInstantiation(Class beanClass, String beanName) throws BeansException;

2.boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException;

3.PropertyValues postProcessPropertyValues(
            PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName)

            throws BeansException;

从表面的意思理解InstantiationAwareBeanPostProcessor实例化前后的处理器，BeanPostProcessor中的方法是初始化类时候的处理器（实例化早于初始化）在spring中初始化指的一般是在调用init-method属性前后。

在AbstractAutowireCapableBeanFactory的createBean方法中

@Override  
protected Object createBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
            throws BeanCreationException {

        if (logger.isDebugEnabled()) {
            logger.debug("Creating instance of bean '" + beanName + "'");
        }
        // Make sure bean class is actually resolved at this point.
        resolveBeanClass(mbd, beanName);

        // Prepare method overrides.
        try {
            mbd.prepareMethodOverrides();
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanDefinitionStoreException(mbd.getResourceDescription(),
                    beanName, "Validation of method overrides failed", ex);
        }

        try {
            // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
            Object bean = resolveBeforeInstantiation(beanName, mbd);
            if (bean != null) {
                return bean;
            }
        }
        catch (Throwable ex) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                    "BeanPostProcessor before instantiation of bean failed", ex);
        }

        Object beanInstance = doCreateBean(beanName, mbd, args);
        if (logger.isDebugEnabled()) {
            logger.debug("Finished creating instance of bean '" + beanName + "'");
        }
        return beanInstance;
}

在resolveBeforeInstantiation方法中会运用实现了InstantiationAwareBeanPostProcessor接口的类实例化前调用postProcessBeforeInstantiation如果返回不为空就会执行所有实现了BeanPostProcessor类（包括实现了InstantiationAwareBeanPostProcessor的类）的postProcessAfterInitialization方法。

在doCreateBean方法中会调用populateBean(String beanName, AbstractBeanDefinition mbd, BeanWrapper bw)该方法主要是用来属性填充的。在开始时会调用实现InstantiationAwareBeanPostProcessor接口类的postProcessAfterInstantiation。返回值还能控制下面是否进行下面的属性填充。没有返回的话后面还会调用postProcessPropertyValues方法

在init-method方法生效前后调用postProcessBeforeInitialization和postProcessAfterInitialization方法

可以看出spring会尽量保证postProcessAfterInitialization能够执行。