Spring之Bean后处理器——InstantiationAwareBeanPostProcessor的使用与源码解析

文章目录

InstantiationAwareBeanPostProcessor介绍
- InstantiationAwareBeanPostProcessor执行流程
InstantiationAwareBeanPostProcessor使用
- Book
- Pen
- BookProxyInstantiationAwareBeanPostProcessor
- main
- 全量代码
- 执行结果
源码解析
总结

InstantiationAwareBeanPostProcessor介绍

InstantiationAwareBeanPostProcessor接口扩展了BeanPostProcessor子接口，提供了Bean被实例化之前、Bean实例化之后、Bean属性装配前更细粒度控制Bean创建流程的处理。

由于InstantiationAwareBeanPostProcessor扩展了BeanPostProcessor接口，所以该篇文章部分内容会与BeanPostProcessor接口的流程重合；尽管如此，也建议在看该篇文章前，先阅读关于BeanPostProcessor接口的详细介绍与源码解析：Spring之Bean后处理器——BeanPostProcessor的使用与源码解析

InstantiationAwareBeanPostProcessor接口比BeanPostProcessor新增了如下方法：

方法	描述
`Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName)`	在`Bean`实例化之前，调用此方法；该方法传入目标`Bean`类型与`BeanName`;该方法可以返回一个该`Bean`类型的对象，或对该`Bean`的一个代理对象；当该方法返回了实例化对象后，后续的所有`Bean`实例化与初始化的动作将不再进行。只会调用后续的`BeanPostProcessor#postProcessAfterInitialization()`方法。
`boolean postProcessAfterInstantiation(Object bean, String beanName)`	在`Bean`实例化之后，调用此方法；该方法传入还没有装配属性的`Bean`对象以及`BeanName`。如果该方法返回`true`，则将跳过后续的属性装配动作，一般应该返回`true`
`PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName)`	在`Bean`实例化之后，装配属性之前，调用此方法；该方法传入在配置期间所配的`PropertyValues`以及`BeanName`。该方法返回的`PropertyValues`将最终装配到`Bean`对象中。

InstantiationAwareBeanPostProcessor执行流程

InstantiationAwareBeanPostProcessor流程如下：

执行Bean实例化之前，执行postProcessBeforeInstantiation();
执行Bean实例化之后执行postProcessAfterInstantiation();
执行Bean属性装配前执行postProcessProperties();
在Bean属性装配后执行postProcessBeforeInitialization();
在Bean的Init相关初始化完毕后执行postProcessAfterInitialization();

下图能比较好的反应出过程:

InstantiationAwareBeanPostProcessor使用

接下来写个例子。全量代码会在最后贴出来，直接CV运行即可。

Book

Book类，它实现了InitializingBean接口，其afterPropertiesSet()方法仅输出一行信息用来记录执行流程；还有一个customInit()方法使其加入到Spring的init-method的执行过程；该类还有一个show()方法，用来在后面的BookProxyInstantiationAwareBeanPostProcessor处理器中对原始的Book对象生成一个代理类，该代理类将对show()方法进行增强处理，用来让咱们的BeanPostProcessor能实际干点事儿。
但是由于BookProxyInstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation()返回了代理对象，所以后续Book后续的初始化都不会在进行，所以其afterPropertiesSet()与customInit()方法也不会再调用。

public class Book implements InitializingBean {private String name;private String author;public String getName() {return name;}public void setName(String name) {this.name = name;}public String getAuthor() {return author;}public void setAuthor(String author) {this.author = author;}public void show() {System.out.printf("book#show():%s\n", this);}public void customInit() {System.out.printf("%-85s：%s{%s}%n", "------Book#customInit", this.getClass().getSimpleName(), this);}@Overridepublic String toString() {return "Book{" +"name='" + name + '\'' +", author='" + author + '\'' +'}';}@Overridepublic void afterPropertiesSet() throws Exception {System.out.printf("%-85s：%s{%s}%n", "------Book#afterPropertiesSet", this.getClass().getSimpleName(), this);}
}

Pen

Pen类与Book类一样，它实现了InitializingBean接口，其afterPropertiesSet()方法仅输出一行信息用来记录执行流程；还有一个customInit()方法使其加入到Spring的init-method的执行过程；

public class Pen implements InitializingBean {private String name;public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return "Pen{" +"name='" + name + '\'' +'}';}public void customInit() {System.out.printf("%-85s：%s{%s}%n", "------Pen#customInit", this.getClass().getSimpleName(), this);}@Overridepublic void afterPropertiesSet() throws Exception {System.out.printf("%-85s：%s{%s}%n", "------Pen#afterPropertiesSet", this.getClass().getSimpleName(), this);}
}

BookProxyInstantiationAwareBeanPostProcessor

BookProxyInstantiationAwareBeanPostProcessor实现了InstantiationAwareBeanPostProcessor接口;在其postProcessBeforeInstantiation()方法中对Book类型进行判断，如果是Book类型则使用CGLIB生成其代理，用来增强Book#show()方法，在其前后各打印一句话。其余方法都仅输出一条信息，用来描述其执行过程。

public class BookProxyInstantiationAwareBeanPostProcessor implements InstantiationAwareBeanPostProcessor {@Overridepublic Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {System.out.printf("%-85s：%s%n", "------BookProxyInstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation", beanClass.getSimpleName());//判断传入的beanClass是否是Book类型if (Book.class.equals(beanClass)) {System.out.printf("\033[1;33m%-85s：对[%s]的\033[1;31mshow()\033[1;33m方法进行增强 \033[0m%n", "------BookProxyInstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation", beanClass.getSimpleName());//创建Book类的代理Enhancer enhancer = new Enhancer();enhancer.setSuperclass(Book.class);enhancer.setCallback((MethodInterceptor) (obj, method, args, methodProxy) -> {//如果不是show()方法则直接调用返回if (!method.equals(Book.class.getMethod("show"))) {return methodProxy.invokeSuper(obj, args);}//对show()做增强处理System.out.printf("\033[1;33m%-70s\033[0m%n", "Book#show()执行前");Object result = methodProxy.invokeSuper(obj, args);System.out.printf("\033[1;33m%-70s\033[0m%n", "Book#show()执行后");return result;});Book book = (Book) enhancer.create();book.setName("《非暴力沟通》");book.setAuthor("马歇尔·卢森堡");return book;}return null;}@Overridepublic boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {System.out.printf("%-85s：%s{%s}%n", "------BookProxyInstantiationAwareBeanPostProcessor#postProcessAfterInstantiation", bean.getClass().getSimpleName(), bean);return true;}@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {System.out.printf("%-85s：%s{%s}%n", "------BookProxyInstantiationAwareBeanPostProcessor#postProcessBeforeInitialization", bean.getClass().getSimpleName(), bean);return bean;}@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {System.out.printf("%-85s：%s{%s}%n", "------BookProxyInstantiationAwareBeanPostProcessor#postProcessAfterInitialization", bean.getClass().getSimpleName(), bean);return bean;}@Overridepublic PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException {System.out.printf("%-85s：%s{%s}%n", "------BookProxyInstantiationAwareBeanPostProcessor#postProcessProperties", bean.getClass().getSimpleName(), bean);pvs.forEach((name) -> {System.out.printf("%85s：%s {%s=%s}%n", "pvs", bean.getClass().getSimpleName(), name.getName(), name.getValue());});return pvs;}
}

main

定义一个Book类型与Pen类型的GenericBeanDefinition，将Book与Pen的customInit()添加到BeanDefinition中，并设置Pen的MutablePropertyValues用于初始化后的属性装配。
同时将BookProxyInstantiationAwareBeanPostProcessor注册到容器中。

public static void main(String[] args) {GenericApplicationContext context = new GenericApplicationContext();//注册Book的BeanDefinitionGenericBeanDefinition bookBeanDefinition = new GenericBeanDefinition();bookBeanDefinition.setBeanClass(Book.class);bookBeanDefinition.setScope(BeanDefinition.SCOPE_SINGLETON);//指定为单例模式bookBeanDefinition.setInitMethodName("customInit");//设置初始化方法context.registerBeanDefinition("book", bookBeanDefinition);//注册Pen的BeanDefinitionGenericBeanDefinition penBeanDefinition = new GenericBeanDefinition();penBeanDefinition.setBeanClass(Pen.class);penBeanDefinition.setScope(BeanDefinition.SCOPE_SINGLETON);//指定为单例模式penBeanDefinition.setInitMethodName("customInit");//设置初始化方法//设置pen属性penBeanDefinition.setPropertyValues(new MutablePropertyValues().addPropertyValue(new PropertyValue("name", "英雄钢笔")));context.registerBeanDefinition("pen", penBeanDefinition);//注册BeanDefinition//注册BookProxyInstantiationAwareBeanPostProcessor后处理器context.registerBean(BookProxyInstantiationAwareBeanPostProcessor.class);//刷新容器context.refresh();//获取Book的bean对象，调用show()方法context.getBean("book", Book.class).show();
}

全量代码

package com.baiyang.beanpostprocessor.instantiationaware;import org.springframework.beans.BeansException;
import org.springframework.beans.MutablePropertyValues;
import org.springframework.beans.PropertyValue;
import org.springframework.beans.PropertyValues;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
import org.springframework.beans.factory.support.GenericBeanDefinition;
import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.context.support.GenericApplicationContext;import java.util.concurrent.atomic.AtomicInteger;public class BookProxyInstantiationAwareBeanPostProcessor implements InstantiationAwareBeanPostProcessor {public static AtomicInteger COUNT = new AtomicInteger();@Overridepublic Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {System.out.printf("%-85s：%s%n", COUNT.addAndGet(1) + "------BookProxyInstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation", beanClass.getSimpleName());//判断传入的beanClass是否是Book类型if (Book.class.equals(beanClass)) {System.out.printf("\033[1;33m%-85s：对[%s]的\033[1;31mshow()\033[1;33m方法进行增强 \033[0m%n", COUNT.addAndGet(1) + "------BookProxyInstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation", beanClass.getSimpleName());//创建Book类的代理Enhancer enhancer = new Enhancer();enhancer.setSuperclass(Book.class);enhancer.setCallback((MethodInterceptor) (obj, method, args, methodProxy) -> {//如果不是show()方法则直接调用返回if (!method.equals(Book.class.getMethod("show"))) {return methodProxy.invokeSuper(obj, args);}//对show()做增强处理System.out.printf("\033[1;33m%-70s\033[0m%n", "Book#show()执行前");Object result = methodProxy.invokeSuper(obj, args);System.out.printf("\033[1;33m%-70s\033[0m%n", "Book#show()执行后");return result;});Book book = (Book) enhancer.create();book.setName("《非暴力沟通》");book.setAuthor("马歇尔·卢森堡");return book;}return null;}@Overridepublic boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {System.out.printf("%-85s：%s{%s}%n", COUNT.addAndGet(1) + "------BookProxyInstantiationAwareBeanPostProcessor#postProcessAfterInstantiation", bean.getClass().getSimpleName(), bean);return true;}@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {System.out.printf("%-85s：%s{%s}%n", COUNT.addAndGet(1) + "------BookProxyInstantiationAwareBeanPostProcessor#postProcessBeforeInitialization", bean.getClass().getSimpleName(), bean);return bean;}@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {System.out.printf("%-85s：%s{%s}%n", COUNT.addAndGet(1) + "------BookProxyInstantiationAwareBeanPostProcessor#postProcessAfterInitialization", bean.getClass().getSimpleName(), bean);return bean;}@Overridepublic PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException {System.out.printf("%-85s：%s{%s}%n", COUNT.addAndGet(1) + "------BookProxyInstantiationAwareBeanPostProcessor#postProcessProperties", bean.getClass().getSimpleName(), bean);pvs.forEach((name) -> {System.out.printf("%85s：%s {%s=%s}%n", "pvs", bean.getClass().getSimpleName(), name.getName(), name.getValue());});return pvs;}public static void main(String[] args) {GenericApplicationContext context = new GenericApplicationContext();//注册Book的BeanDefinitionGenericBeanDefinition bookBeanDefinition = new GenericBeanDefinition();bookBeanDefinition.setBeanClass(Book.class);bookBeanDefinition.setScope(BeanDefinition.SCOPE_SINGLETON);//指定为单例模式bookBeanDefinition.setInitMethodName("customInit");//设置初始化方法context.registerBeanDefinition("book", bookBeanDefinition);//注册Pen的BeanDefinitionGenericBeanDefinition penBeanDefinition = new GenericBeanDefinition();penBeanDefinition.setBeanClass(Pen.class);penBeanDefinition.setScope(BeanDefinition.SCOPE_SINGLETON);//指定为单例模式penBeanDefinition.setInitMethodName("customInit");//设置初始化方法//设置pen属性penBeanDefinition.setPropertyValues(new MutablePropertyValues().addPropertyValue(new PropertyValue("name", "英雄钢笔")));context.registerBeanDefinition("pen", penBeanDefinition);//注册BeanDefinition//注册BookProxyInstantiationAwareBeanPostProcessor后处理器context.registerBean(BookProxyInstantiationAwareBeanPostProcessor.class);//刷新容器context.refresh();//获取Book的bean对象，调用show()方法context.getBean("book", Book.class).show();}static class Book implements InitializingBean {private String name;private String author;public String getName() {return name;}public void setName(String name) {this.name = name;}public String getAuthor() {return author;}public void setAuthor(String author) {this.author = author;}public void show() {System.out.printf("book#show():%s\n", this);}public void customInit() {System.out.printf("%-85s：%s{%s}%n", COUNT.addAndGet(1) + "------Book#customInit", this.getClass().getSimpleName(), this);}@Overridepublic String toString() {return "Book{" +"name='" + name + '\'' +", author='" + author + '\'' +'}';}@Overridepublic void afterPropertiesSet() throws Exception {System.out.printf("%-85s：%s{%s}%n", COUNT.addAndGet(1) + "------Book#afterPropertiesSet", this.getClass().getSimpleName(), this);}}static class Pen implements InitializingBean {private String name;public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return "Pen{" +"name='" + name + '\'' +'}';}public void customInit() {System.out.printf("%-85s：%s{%s}%n", COUNT.addAndGet(1) + "------Pen#customInit", this.getClass().getSimpleName(), this);}@Overridepublic void afterPropertiesSet() throws Exception {System.out.printf("%-85s：%s{%s}%n", COUNT.addAndGet(1) + "------Pen#afterPropertiesSet", this.getClass().getSimpleName(), this);}}
}

执行结果

从执行结果即可反应出InstantiationAwareBeanPostProcessor的执行流程：

1~3行的结果是加载Book的输出，由于BookProxyInstantiationAwareBeanPostProcessor在执行postProcessBeforeInstantiation方法之后返回了Book的代理对象，所以后续对Book的所有初始化将不再继续，调用了BeanDefinition#postProcessAfterInitialization之后就直接返回注册了。
4~10行的输出结果可以看出，Pen类的加载，由于没有任何InstantiationAwareBeanPostProcessor对其做任何处理，所以走完了所有的常规Bean加载流程。
最后三行输出执行了从容器中获取的book对象的show()方法，可以看出我们通过BookProxyInstantiationAwareBeanPostProcessor成功的改变了原本注入到容器中的Book对象，并成功对其show()方法进行了增强处理。

源码解析

spring版本：5.2.9

该节源码解析仅仅只讲关键的与InstantiationAwareBeanPostProcessor相关的位置。如果想要知其与InstantiationAwareBeanPostProcessor前后的细节，可以针对本节的所讲述的位置自行Debug进入详细阅读。

首先是Spring容器的经典入口：refresh()

然后调用AbstractApplicationContext所持有的实际BeanFactory(DefaultListableBeanFactory)句柄的preInstantiateSingletons()做Bean容器的初始化工作。

org.springframework.beans.factory.support.DefaultListableBeanFactory#preInstantiateSingletons:
bean的创建流程：getBean()->doGetBean()->createBean()->doCreateBean()
我们直接定位到createBean()

从上面的流程可以看出，当执行了resolveBeforeInstantiation(beanName,mbdToUse)方法后，有返回bean对象，则直接return出去了。
如果没有返回bean对象，则会执行doCreateBean()进行真正的常规创建流程。

在本文章的例子中，初始化book对象的流程中BookProxyInstantiationAwareBeanPostProcessor的postProcessBeforeInstantiation()返回了book的代理对象，所以在上面的流程中，直接返回出去了，没有执行doCreateBean()方法。

接下进入resolveBeforeInstantiation(beanName,mbdToUse)：

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#applyBeanPostProcessorsBeforeInstantiation

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#applyBeanPostProcessorsAfterInitialization

createBean()将对象返回出去，一路回到getSingleton():
org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, org.springframework.beans.factory.ObjectFactory<?>)

可以看到此时，已经将一个经过了InstantiationAwareBeanPostProcessor处理的Bean对象注册到了BeanFactory中(在本例子里面是我们的BookProxyInstantiationAwareBeanPostProcessor创建的Book对象的代理类)。

经过以上流程可以看出，当InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation()如果返回了对象的话，那么Bean的创建流程将会直接结束返回该对象。

接下来讲InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation()不返回对象的Bean创建流程，在该例子里面是Pen的创建流程：

上面的流程中，由于执行了BookProxyInstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation()没有返回对象，所以会执行后面的doCreateBean()来创建对象。

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#doCreateBean

在上面的流程中，先通过反射创建了对象，然后调用populateBean()进行属性装配，属性装配后，执行Bean的初始化流程，包含了BeanPostProcessor的前后置处理、init-method相关处理。

我们知道，在InstantiationAwareBeanPostProcessor中目前还只执行了postProcessBeforeInstantiation()，还有剩下postProcessAfterInstantiation()、postProcessProperties()、postProcessBeforeInitialization()、postProcessAfterInitialization()没有执行。

我们先看populateBean()中的逻辑：
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#populateBean

从上面的流程可以看出，populateBean()的流程是先调用InstantiationAwareBeanPostProcessor#postProcessAfterInstantiation()，然后调用其InstantiationAwareBeanPostProcessor#postProcessPropertyValues()，最后进行属性的装配工作。
此时和我们前面描述的执行流程保持一致。

接下来是postProcessBeforeInitialization()、postProcessAfterInitialization()的执行还没有做。
返回到上层

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#initializeBean(java.lang.String, java.lang.Object, org.springframework.beans.factory.support.RootBeanDefinition):

从上面的initializeBean()的流程可以看到我们首先调用了BeanPostProcessor#postProcessBeforeInitialization()，然后执行了invokeInitMethods()来处理bean的实现的InitializingBean接口的afterPropertiesSet()与自定义init-method；最后执行BeanPostProcessor#postProcessAfterInitialization();

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#applyBeanPostProcessorsBeforeInitialization

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#invokeInitMethods

从上面的invokeInitMethods()可以看到包含了InitializingBean接口的处理与init-method的方法处理流程；
init-method方法最终会通过反射执行。

最后就是BeanPostProcessor#postProcessAfterInitialization()方法的执行：

至此，所有的InstantiationAwareBeanPostProcessor接口涉及到的流程都执行完毕，与前面讲述的流程一样，最后就是返回到getSingleton()将最后最终的对象注册到容器中。

总结

以上通过围绕InstantiationAwareBeanPostProcessor创建一个对指定Bean对象的代理对象，对其特定方法进行代理增强的例子，来介绍了InstantiationAwareBeanPostProcessor的应用，以及描述了InstantiationAwareBeanPostProcessor的"短路"会控制到后续常规Bean的创建流程。
同时，通过对源码的浅析来对InstantiationAwareBeanPostProcessor的执行前后流程进行了讲解。