Spring源码–BeanFactoryPostProcessor
对于BeanFactoryPostProcessor下面是官方api文档给出的定义：
连接工厂允许修改自定义应用的bean信息，可以调整底层bean工厂的属性值。（Factory hook that allows for custom modification of an application context's bean definitions, adapting the bean property values of the context's underlying bean factory.）
从上面 的文档上看就是可以修改bean信息，但是修改的触发节点是在bean实例化前才会有效果 。看下BeanFactoryPostProcessor的源码：
public interface BeanFactoryPostProcessor {
void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;
}从源码中可以看出，这个接口只有一个接口，所有的实现都是集成这个接口，下面 是实现接口的对应类型。
下面看下这个其中一个的源码：
public BeanFactoryPostProcessor beanFactoryPostProcessor() {
return new BeanFactoryPostProcessor() {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
BeanDefinition bd = beanFactory.getBeanDefinition("beanPostProcessor");
bd.getPropertyValues().addPropertyValue("nameSuffix", "-processed-" + myProp);
}
};
}以上核心代码只有两个句，第一步：BeanDefinition bd = beanFactory.getBeanDefinition(“beanPostProcessor”);通过bean工厂 获取到BeanDefinition的对象。第二步：bd.getPropertyValues().addPropertyValue(“nameSuffix”, “-processed-” + myProp);对于bean加入 属性。
下面我们举个栗子，看下BeanFactoryPostProcessor使用情况：
集成BeanFactoryPostProcessor接口，实现重写postProcessBeanFactory方法：
public class NameBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("-->NameBeanFactoryPostProcessor start");
String[] names = beanFactory.getBeanDefinitionNames();
for (String name : names) {
if("a".equals(name)){
BeanDefinition beanDefinition = beanFactory.getBeanDefinition(name);
MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();
if(propertyValues.contains("name")){
propertyValues.addPropertyValue("name", "王五");
System.out.println("-->mod bean definition name");
}
}
}
System.out.println("-->NameBeanFactoryPostProcessor end");
}
}执行触发方法：
public class TestAB {
public static void main(String[] args) {
ApplicationContext applicationContext= new ClassPathXmlApplicationContext("x.xml");
A a=applicationContext.getBean(A.class);
System.out.println("-->NameBeanFactoryPostProcessor test end!");
System.out.println("-->name :"+ a.getName());
}
}看下A类的xml的文件内容：
<bean id="a" class="org.springframework.test.debug.A">
<property name="name" value="张三"></property>
</bean>
执行结果：
-->NameBeanFactoryPostProcessor start
-->mod bean definition name
-->NameBeanFactoryPostProcessor end
-->BeanFactoryPostProcessor test end!
-->name :王五
A类的属性被修改了 , 从张三 -> 王五。
下面思考一个问题，如果有多个BeanFactoryPostProcessor存在怎么办？
这时候给A类加一个age属性，再添加AgeBeanFactoryPostProcessor，这时有两个BeanFactoryPostProcessor，这时就用到了我们之前降到的AbstractApplicationContext实现类中的refresh方法，在refresh方法中有进行，回顾一下refresh方法与beanFactory相关的四个方法：
//创建
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
//准备
prepareBeanFactory(beanFactory);
//空方法
postProcessBeanFactory(beanFactory);
//处理逻辑
invokeBeanFactoryPostProcessors(beanFactory);
进入invokeBeanFactoryPostProcessors(beanFactory)展示源码：
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
//逻辑处理
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
//后续处理
if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
}在进入PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());方法中，查看源码
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
//......省略了部分代码，代码太长了，了解这块内容看这里就行了
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
//首先，调用实现 PriorityOrdered 的 BeanFactoryPostProcessor。
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
//接下来，调用实现 Ordered 的 BeanFactoryPostProcessors。
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
sortPostProcessors(orderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// Finally, invoke all other BeanFactoryPostProcessors.
//最后，调用所有其他 BeanFactoryPostProcessor。
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
for (String postProcessorName : nonOrderedPostProcessorNames) {
nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
}
在上面源码中可以看出，在执行优先级 实现PriorityOrdered > 实现Ordered > 其他 。所以PriorityOrdered 和Ordered 是影响BeanFactoryPostProcessors执行顺序的最终因素。下面看下PriorityOrdered 和Ordered 源码：
public interface PriorityOrdered extends Ordered {
}
public interface Ordered {
int HIGHEST_PRECEDENCE = Integer.MIN_VALUE;
int LOWEST_PRECEDENCE = Integer.MAX_VALUE;
/**
* Get the order value of this object.
* <p>Higher values are interpreted as lower priority. As a consequence,
* the object with the lowest value has the highest priority (somewhat
* analogous to Servlet {@code load-on-startup} values).
* <p>Same order values will result in arbitrary sort positions for the
* affected objects.
* @return the order value
* @see #HIGHEST_PRECEDENCE
* @see #LOWEST_PRECEDENCE
*/
int getOrder();
}从源码上可以看出来PriorityOrdered是继承了Ordered接口，所以下面我们以Ordered接口为例，去验证多个BeanFactoryPostProcessors类。
NameBeanFactoryPostProcessor类
public class NameBeanFactoryPostProcessor implements BeanFactoryPostProcessor, Ordered {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("-->NameBeanFactoryPostProcessor start");
String[] names = beanFactory.getBeanDefinitionNames();
for (String name : names) {
if("a".equals(name)){
BeanDefinition beanDefinition = beanFactory.getBeanDefinition(name);
MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();
if(propertyValues.contains("name")){
propertyValues.addPropertyValue("name", "王五");
System.out.println("-->mod bean definition name");
}
}
}
System.out.println("-->NameBeanFactoryPostProcessor end");
}
@Override
public int getOrder() {
return 1;
}
}AgeBeanFactoryPostProcessor类
public class AgeBeanFactoryPostProcessor implements BeanFactoryPostProcessor, Ordered {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("-->AgeBeanFactoryPostProcessor start");
String[] names = beanFactory.getBeanDefinitionNames();
for (String name : names) {
if("a".equals(name)){
BeanDefinition beanDefinition = beanFactory.getBeanDefinition(name);
MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();
if(propertyValues.contains("name")){
propertyValues.addPropertyValue("age", 12);
System.out.println("-->mod bean definition age");
}
}
}
System.out.println("-->AgeBeanFactoryPostProcessor end");
}
@Override
public int getOrder() {
return 2;
}
}x.xml文件
<bean id="a" class="org.springframework.test.debug.A">
<property name="name" value="张三"></property>
<property name="age" value="16"></property>
</bean>
<!-- 注册BeanFactoryPostProcessor -->
<bean class="org.springframework.test.debug.NameBeanFactoryPostProcessor"></bean>
<bean class="org.springframework.test.debug.AgeBeanFactoryPostProcessor"></bean>
启动方法
public static void main(String[] args) {
ApplicationContext applicationContext= new ClassPathXmlApplicationContext("x.xml");
A a=applicationContext.getBean(A.class);
System.out.println("-->BeanFactoryPostProcessor test end!");
System.out.println("-->name :"+ a.getName());
System.out.println("-->age :"+ a.getAge());
}执行结果
-->NameBeanFactoryPostProcessor start
-->mod bean definition name
-->NameBeanFactoryPostProcessor end
-->AgeBeanFactoryPostProcessor start
-->mod bean definition age
-->AgeBeanFactoryPostProcessor end
-->BeanFactoryPostProcessor test end!
-->name :王五
-->age :12
从输出结果上看确实是先执行的NameBeanFactoryPostProcessor，后置执行的AgeBeanFactoryPostProcessor，与设置的order数字是一致的。
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