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feat(spring): add BeanFactoryPostProcessor (#125)

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README.md
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- [将 bean 解析封装成 BeanDefinition](/docs/Spring/IoC/2、将bean解析封装成BeanDefinition.md)
- [将 BeanDefinition 注册进 IoC 容器](/docs/Spring/IoC/3、将BeanDefinition注册进IoC容器.md)
- [依赖注入(DI)](</docs/Spring/IoC/4、依赖注入(DI).md>)
- [BeanFactoryPostProcessor](/docs/Spring/IoC/BeanFactoryPostProcessor.md)
- [BeanPostProcessor](/docs/Spring/IoC/BeanPostProcessor.md)
- [Spring BeanFactory 源码解析](/docs/Spring/clazz/Spring-beanFactory.md)

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docs/Spring/IoC/BeanFactoryPostProcessor.md
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BeanFactoryBeanPostProcessor 是当 BeanDefinition 读取完元数据（也就是从任意资源中定义的 bean 数据）后还未实例化之前可以进行修改
抄录并翻译官方的语句
> `BeanFactoryPostProcessor` 操作 bean 的元数据配置. 也就是说,Spring IoC 容器允许 `BeanFactoryPostProcessor` 读取配置元数据, 并可能在容器实例化除 `BeanFactoryPostProcessor` 实例之外的任何 bean _之前_ 更改它
tip:
> 在 `BeanFactoryPostProcessor` (例如使用 `BeanFactory.getBean()`) 中使用这些 bean 的实例虽然在技术上是可行的,但这么来做会将 bean 过早实例化, 这违反了标准的容器生命周期. 同时也会引发一些副作用,例如绕过 bean 的后置处理。
```java
public interface BeanFactoryPostProcessor {
/**
*通过ConfigurableListableBeanFactory这个可配置的BeanFactory对我们的bean原数据进行修改
*/
void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;
}
```
#### BeanFactoryPostProcessor 执行时期的探究
ApplicationContext 的 refresh() 中的 invokeBeanFactoryPostProcessors 方法就开始创建我们的 BFPP(BeanFactoryPostProcessor)了
具体执行方法 invokeBeanFactoryPostProcessors，虽然一百多行代码，其实只需要特别了解的地方就几处。
```java
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
Set<String> processedBeans = new HashSet<>();
// 由于我们的beanFactory是DefaultListableBeanFactory实例是BeanDefinitionRegistry的子类所以可以进来
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
registryProcessor.postProcessBeanDefinitionRegistry(registry);
registryProcessors.add(registryProcessor);
}
else {
regularPostProcessors.add(postProcessor);
}
}
// BeanDefinitionRegistryPostProcessor是BFPP的子类但是比BFPP提前执行
// 顺序实现PriorityOrdered接口先被执行，然后是Ordered接口，最后是什么都没实现的BeanDefinitionRegistryPostProcessor
/**
*都有beanFactory.getBean方法，证明BeanDefinitionRegistryPostProcessor这个bean现在已经被创建了
*/
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
currentRegistryProcessors.clear();
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
currentRegistryProcessors.clear();
boolean reiterate = true;
while (reiterate) {
reiterate = false;
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
reiterate = true;
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
currentRegistryProcessors.clear();
}
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}
// BFPP的执行顺序与上一样
/**
*都有beanFactory.getBean方法，证明BFPP这个bean现在已经被创建了
*/
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
List<String> orderedPostProcessorNames = new ArrayList<>();
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
for (String ppName : postProcessorNames) {
if (processedBeans.contains(ppName)) {
}
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
sortPostProcessors(orderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
for (String postProcessorName : nonOrderedPostProcessorNames) {
nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
beanFactory.clearMetadataCache();
}
```
我们可以具体分析一下 BeanFactoryPostProcessor 的子类 CustomEditorConfigurer 自定义属性编辑器来巩固一下执行流程
所谓属性编辑器是当你要自定义更改配置文件中的属性属性时，如 String 类型转为 Date 或者其他，下面的一个小例子展示如何 String 类型的属性怎么转化为 Address 属性
#### 简单工程（Spirng-version-5.3.18)
Person 类
```java
package cn.demo1;
import lombok.Getter;
import lombok.Setter;
@Setter
@Getter
@ToString
public class Person {
private String name;
private Address address;
}
```
Address 类
```java
package cn.demo1;
@Setter
@Getter
@ToString
public class Address {
private String city;
private String town;
}
```
AddressParse 类
```java
package cn.demo1;
import java.beans.PropertyEditorSupport;
public class AddressParse extends PropertyEditorSupport {
@Override
public void setAsText(String text) throws IllegalArgumentException {
final String[] vals = text.split(",");
Address addr = new Address();
addr.setProvince(vals[0]);
addr.setCity(vals[1]);
setValue(addr);
}
}
```
MyCustomEditor 类
```java
package cn.demo1;
import org.springframework.beans.PropertyEditorRegistrar;
import org.springframework.beans.PropertyEditorRegistry;
public class MyCustomEditor implements PropertyEditorRegistrar {
@Override
public void registerCustomEditors(PropertyEditorRegistry registry) {
registry.registerCustomEditor(Address.class, new AddressParse());
}
}
```
配置文件 test1.xml
```java
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/aop https://www.springframework.org/schema/aop/spring-aop.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
<!-- 待属性编辑的bean，value代表的就是string类型-->
<bean class="cn.demo1.Person" id="person">
<property name="name" value="李华"/>
<property name="address" value="四川,成都"/>
</bean>
<!-- 注册属性编辑器-->
<bean class="org.springframework.beans.factory.config.CustomEditorConfigurer" id="configurer">
<property name="propertyEditorRegistrars">
<list>
<bean class="cn.demo1.MyCustomEditor"/>
</list>
</property>
</bean>
</beans>
```
测试类 EdT
```java
package cn.test1;
import cn.demo1.Person;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class EdT {
@Test
public void test1() {
ApplicationContext context = new ClassPathXmlApplicationContext("test1.xml");
final Person bean = context.getBean(Person.class);
System.out.println(bean);
}
}
=====================测试结果
Person(name=李华, address=Address(province=四川, city=成都))
```
可以看见我们成功的将 String 类型转化为 Address 类型，让我们来看看实现流程，
- 首先实现 PropertyEditorSupport 来自定义属性编辑规则
- 其次将你的编辑规则给到 PropertyEditorRegistrar 子类里进行注册
- 最后在 Spring 中配置 CustomEditorConfigurer 类然后注入你的 PropertyEditorRegistrar 注册器
让我们 debug 走一遍
如果你已经耐心看完上面的`BeanFactoryPostProcessor执行时期的探究`那么你应该可以知道接下来我们的步骤应该是进入 invokeBeanFactoryPostProcessors 这个方法里了
```java
private static void invokeBeanFactoryPostProcessors(
Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) {
for (BeanFactoryPostProcessor postProcessor : postProcessors) {
StartupStep postProcessBeanFactory = beanFactory.getApplicationStartup().start("spring.context.bean-factory.post-process")
.tag("postProcessor", postProcessor::toString);
postProcessor.postProcessBeanFactory(beanFactory);
postProcessBeanFactory.end();
}
}
```
很明显它执行 postProcessBeanFactory 这个方法
我们探究的 BFPP 正是 CustomEditorConfigurer，所以这个是 CustomEditorConfigurer 对 BFPP 的 postProcessBeanFactory 实现
```java
// 必然有个set方法让我们进行注入
public void setPropertyEditorRegistrars(PropertyEditorRegistrar[] propertyEditorRegistrars) {
this.propertyEditorRegistrars = propertyEditorRegistrars;
}
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
if (this.propertyEditorRegistrars != null) {
for (PropertyEditorRegistrar propertyEditorRegistrar : this.propertyEditorRegistrars) {
// 把它加入Bean工厂里后面可以进行调用
private final Set<PropertyEditorRegistrar> propertyEditorRegistrars = new LinkedHashSet<>(4);
beanFactory.addPropertyEditorRegistrar(propertyEditorRegistrar);
}
}
if (this.customEditors != null) {
this.customEditors.forEach(beanFactory::registerCustomEditor);
}
}
```
关于这个注册器使用要到后面填充属性的时候才会用到，
> 我其实觉得这个有点瑕疵，因为 BFPP 作用影响应该是当 Spring 还未创建 bean 的时候，可以用 BFPP 进行修改操作，可是这个属性编辑却影响了 bean 创建过后的修改操作，那么它就替代了 BPP（BeanPostProcessor)的作用发挥了。（以上仅仅代表个人的观点，有可能是我想错了）
当我们 debug 到 AbstractAutowireCapableBeanFactory 的 populateBean 这个方法填充 bean 的属性的时候，
让我们看看它的方法，其中我省略了大部分无关代码
```java
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
// 这个是如果你配置的bean中有属性值的话
// 也就是如下的配置，那么pvs不会为空的
/**
<bean class="cn.demo1.Person" id="person">
<property name="name" value="李华"/>
<property name="address" value="四川,成都"/>
</bean>
*/
PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
if (pvs != null) {
// 属性操作
applyPropertyValues(beanName, mbd, bw, pvs);
}
}
```
让我们继续看看 applyPropertyValues 这个方法，无关的代码我也给省略了
```java
protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
// PropertyValues接口的默认实现。允许对属性进行简单操作，并提供构造函数以支持从 Map 进行深度复制和构造。
MutablePropertyValues mpvs = null;
List<PropertyValue> original;
// 可以进去
if (pvs instanceof MutablePropertyValues) {
mpvs = (MutablePropertyValues) pvs;
// 默认为false，即我们需要类型转换
if (mpvs.isConverted()) {
// Shortcut: use the pre-converted values as-is.
try {
bw.setPropertyValues(mpvs);
return;
}
catch (BeansException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Error setting property values", ex);
}
}
// 把bean的属性以列表的形式展示出来
original = mpvs.getPropertyValueList();
}
else {
original = Arrays.asList(pvs.getPropertyValues());
}
// 默认为空
TypeConverter converter = getCustomTypeConverter();
if (converter == null) {
converter = bw;
}
// 就一个组合类，帮助更好的bean的属性的解析
BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);
// 深拷贝
List<PropertyValue> deepCopy = new ArrayList<>(original.size());
boolean resolveNecessary = false;
for (PropertyValue pv : original) {
if (pv.isConverted()) {
deepCopy.add(pv);
}
else {
// 获取bean的属性名字
String propertyName = pv.getName();
//获取bean属性值的包装对象
Object originalValue = pv.getValue();
// 自动装配的事情
if (originalValue == AutowiredPropertyMarker.INSTANCE) {
Method writeMethod = bw.getPropertyDescriptor(propertyName).getWriteMethod();
if (writeMethod == null) {
throw new IllegalArgumentException("Autowire marker for property without write method: " + pv);
}
originalValue = new DependencyDescriptor(new MethodParameter(writeMethod, 0), true);
}
// 把bean的属性值从包装类中分离出来
Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
Object convertedValue = resolvedValue;
// 一般为true
boolean convertible = bw.isWritableProperty(propertyName) &&
!PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
if (convertible) {
// 这个就是重点，对应我们的属性转化
convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
}
}
```
继续追踪
```java
@Nullable
private Object convertForProperty(
@Nullable Object value, String propertyName, BeanWrapper bw, TypeConverter converter) {
// BeanWrapperImpl是继承TypeConverter的
if (converter instanceof BeanWrapperImpl) {
// 所以执行下面的方法
return ((BeanWrapperImpl) converter).convertForProperty(value, propertyName);
}
else {
PropertyDescriptor pd = bw.getPropertyDescriptor(propertyName);
MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd);
return converter.convertIfNecessary(value, pd.getPropertyType(), methodParam);
}
}
```
```java
@Nullable
public Object convertForProperty(@Nullable Object value, String propertyName) throws TypeMismatchException {
CachedIntrospectionResults cachedIntrospectionResults = getCachedIntrospectionResults();
PropertyDescriptor pd = cachedIntrospectionResults.getPropertyDescriptor(propertyName);
if (pd == null) {
throw new InvalidPropertyException(getRootClass(), getNestedPath() + propertyName,
"No property '" + propertyName + "' found");
}
TypeDescriptor td = cachedIntrospectionResults.getTypeDescriptor(pd);
if (td == null) {
td = cachedIntrospectionResults.addTypeDescriptor(pd, new TypeDescriptor(property(pd)));
}
// 上面的工作不用管，全是一些前戏工作，这个才是主题，至此我们的流程就到这里结束吧
// 后面的流程太多了，大部分都是处理细节，你只需要知道大概的脉络就行，就是最终它肯定会
// 走到AddressParse这个核心处理
return convertForProperty(propertyName, null, value, td);
}
```
你可以自己可以尝试 debug 一下，看别人实践真的不如自己动手实践一下，Spring 的包装类实属太多，但是可以抓住核心流程进行 debug。
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