spring中BeanPostProcessor之一：InstantiationAwareBeanPostProcessor（03）

前面介绍了InstantiationAwareBeanPostProcessor后置处理器的postProcessBeforeInstantiation和postProcessAfterInstantiation两个方法的用法和使用场景等。在InstantiationAwareBeanPostProcessor中还有两个方法，分别是postProcessProperties和postProcessPropertyValues，从这两个方法的名称上来看，它们完成的功能似乎很相近，下面来看具体的方法。

一、概述

在InstantiationAwarePostProcessor接口中的两个方法如下，

二、详述

在InstantiationAwareBeanPostProcessor接口中找到两个方法的定义如下，

/**
     * Post-process the given property values before the factory applies them
     * to the given bean, without any need for property descriptors.
     * 
Implementations should return {@code null} (the default) if they provide a custom
     * {@link #postProcessPropertyValues} implementation, and {@code pvs} otherwise.
     * In a future version of this interface (with {@link #postProcessPropertyValues} removed),
     * the default implementation will return the given {@code pvs} as-is directly.
     * @param pvs the property values that the factory is about to apply (never {@code null})
     * @param bean the bean instance created, but whose properties have not yet been set
     * @param beanName the name of the bean
     * @return the actual property values to apply to the given bean (can be the passed-in
     * PropertyValues instance), or {@code null} which proceeds with the existing properties
     * but specifically continues with a call to {@link #postProcessPropertyValues}
     * (requiring initialized {@code PropertyDescriptor}s for the current bean class)
     * @throws org.springframework.beans.BeansException in case of errors
     * @since 5.1
     * @see #postProcessPropertyValues
     */
    @Nullable
    default PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName)
            throws BeansException {

        return null;
    }

上面的是postProcessProperties方法，我这里贴出了方法的注释，从注释中我们可以看出该方法从5.1版本后才有。下面看postProcessPropertyValues方法，

/**
     * Post-process the given property values before the factory applies them
     * to the given bean. Allows for checking whether all dependencies have been
     * satisfied, for example based on a "Required" annotation on bean property setters.
     * 
Also allows for replacing the property values to apply, typically through
     * creating a new MutablePropertyValues instance based on the original PropertyValues,
     * adding or removing specific values.
     * 
The default implementation returns the given {@code pvs} as-is.
     * @param pvs the property values that the factory is about to apply (never {@code null})
     * @param pds the relevant property descriptors for the target bean (with ignored
     * dependency types - which the factory handles specifically - already filtered out)
     * @param bean the bean instance created, but whose properties have not yet been set
     * @param beanName the name of the bean
     * @return the actual property values to apply to the given bean (can be the passed-in
     * PropertyValues instance), or {@code null} to skip property population
     * @throws org.springframework.beans.BeansException in case of errors
     * @see #postProcessProperties
     * @see org.springframework.beans.MutablePropertyValues
     * @deprecated as of 5.1, in favor of {@link #postProcessProperties(PropertyValues, Object, String)}
     */
    @Deprecated
    @Nullable
    default PropertyValues postProcessPropertyValues(
            PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {

        return pvs;
    }

从上面可以看出该方法上已经被标记为@Deprecated即为废弃的，且是从5.1开始才被废弃的。也就是说从5.1开始均使用postProcessProperties方法。

既然，在5.1之后postProcessPropertyValues方法已废弃，使用的postProcessPropertiesf方法，那么他们的功能肯定是一样的，那么就只看postProcessProperties方法即可。

postProcessProperties方法要完成的工作是处理类中的属性，并为属性赋值，在spring中已经有相应的实现，CommonAnnotationBeanPostProcessor和AutowiredAnnotationBeanPostProcessor两个实现便可以完成这些工作。这里就不再列举详细的使用方式，下面会具体分析CommonAnnotationBeanPostProcessor和AutowiredAnnotationBeanPostProcessor两个实现类的具体实现，以及这两个类分别完成的功能。

三、使用场合

如果需要使用自定义的spring框架，在进行属性注入的时候不想使用spring的方式，这里可以选择实现InstantiationAwareBeanPostProcessor接口，实现postProcessProperties方法，自己实现属性注入的方式。不过最好还是使用spring内部已经实现好的类。