spring中BeanPostProcessor之一：InstantiationAwareBeanPostProcessor（03）

前面介紹了InstantiationAwareBeanPostProcessor后置處理器的postProcessBeforeInstantiation和postProcessAfterInstantiation兩個方法的用法和使用場景等。在InstantiationAwareBeanPostProcessor中還有兩個方法，分別是postProcessProperties和postProcessPropertyValues，從這兩個方法的名稱上來看，它們完成的功能似乎很相近，下面來看具體的方法。

一、概述

在InstantiationAwarePostProcessor接口中的兩個方法如下，

二、詳述

在InstantiationAwareBeanPostProcessor接口中找到兩個方法的定義如下，

/**
     * Post-process the given property values before the factory applies them
     * to the given bean, without any need for property descriptors.
     * <p>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，我這里貼出了方法的注釋，從注釋中我們可以看出該方法從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.
     * <p>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.
     * <p>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;
    }

從上面可以看出該方法上已經被標記為@Deprecated即為廢棄的，且是從5.1開始才被廢棄的。也就是說從5.1開始均使用postProcessProperties方法。

既然，在5.1之后postProcessPropertyValues方法已廢棄，使用的postProcessPropertiesf方法，那么他們的功能肯定是一樣的，那么就只看postProcessProperties方法即可。

postProcessProperties方法要完成的工作是處理類中的屬性，並為屬性賦值，在spring中已經有相應的實現，CommonAnnotationBeanPostProcessor和AutowiredAnnotationBeanPostProcessor兩個實現便可以完成這些工作。這里就不再列舉詳細的使用方式，下面會具體分析CommonAnnotationBeanPostProcessor和AutowiredAnnotationBeanPostProcessor兩個實現類的具體實現，以及這兩個類分別完成的功能。

三、使用場合

如果需要使用自定義的spring框架，在進行屬性注入的時候不想使用spring的方式，這里可以選擇實現InstantiationAwareBeanPostProcessor接口，實現postProcessProperties方法，自己實現屬性注入的方式。不過最好還是使用spring內部已經實現好的類。