Spring源码分析-BeanFactoryPostProcessor

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Spring源码分析-BeanFactoryPostProcessor

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BeanFactoryPostProcessor接口是Spring提供的对Bean的扩展点,它的子接口是BeanDefinitionRegistryPostProcessor

@FunctionalInterface
public interface BeanFactoryPostProcessor {
    void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;
}


public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {
	void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;
}

BeanFactoryPostProcessor简单使用

BeanFactoryPostProcessor的执行时机是在Spring扫描完成后,Bean初始化前,当我们实现BeanFactoryPostProcessor接口,可以在Bean的初始化之前对Bean进行属性的修改

@Component
public class A {
}

@Component
public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
		BeanDefinition beanDefinition = beanFactory.getBeanDefinition("a");
		beanDefinition.setScope("prototype");
	}
}

@Configuration
@ComponentScan("com.jame")
public class Myconfig {
}

public class MyTest {
	public static void main(String[] args)  {
		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(Myconfig.class);
		A a = context.getBean(A.class);
		A a1 = context.getBean(A.class);
		System.out.println(a==a1);
    }
}

输出结果为:false

上面的例子我们将A的BeanDefinition的scope设置为原型,默认没有设置scope的情况下bean的scope都是单例,也就是说我们成功的修改了A对象的beanDefinition,能修改的属性不止这一个,还有是否懒加载,初始化方法名称,设置属性等等

而它的子类BeanDefinitionRegistryPostProcessor可以对spring容器中的BeanDefinition进行操作

不了解BeanDefinition的可以先简单理解为包装Java类的一个类,例如我们给类设置的是否单例,是否懒加载这些信息都需要存储,而spring就创建一个BeanDefinition,用来存储除了java类以外的其他信息

BeanDefinitionRegistryPostProcessor简单使用

@Component
public class A {
}

public class B  {
}

@Component
public class MyBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {

	@Override
	public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
		RootBeanDefinition beanDefinition = new RootBeanDefinition(B.class);
		registry.registerBeanDefinition("b",beanDefinition);
		registry.removeBeanDefinition("a");
	}

	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
	}
}

@Configuration
@ComponentScan("com.jame")
public class Myconfig {
}

public class MyTest {
	public static void main(String[] args)  {
		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(Myconfig.class);
		B b = context.getBean(B.class);
		System.out.println(b);
		A a = context.getBean(A.class);
    }
}

输出结果:

com.jame.pojo.B@2ac1fdc4
Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.jame.pojo.A' available......

上面的代码中我们对A类加上了@Component,B类什么都没有加,结果应该是A获取到正常输出,然后获取B时报错找不到,但是结果恰恰相反,因为我们在MyBeanDefinitionRegistryPostProcessor类中对Spring管理的Bean进行了修改,新增了一个B的BeanDefinition,删除了A的BeanDefinition,所以结果就如上面呈现的那样

完成了上面的简单使用案例接下来就开始看Spring的执行原理是什么

源码分析

首先第一步要知道什么时候执行的上面的代码,为了方便就不将查找过程粘贴出来了,可以在实现类中输出句话,Debug看看是在那个方法中输出的

public AnnotationConfigApplicationContext(Class<?>... componentClasses) {
   this();
   register(componentClasses);
   refresh();
}

进入refresh方法

@Override
public void refresh() throws BeansException, IllegalStateException {
......
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);

// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);

// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
........
}
}

进入invokeBeanFactoryPostProcessors方法

public static void invokeBeanFactoryPostProcessors(
			ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {

		Set<String> processedBeans = new HashSet<>();

		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);
				}
			}
            
			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);
			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);
			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);
				currentRegistryProcessors.clear();
			}

			invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
			invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
		} else {
			invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
		}

		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<>();
		for (String postProcessorName : orderedPostProcessorNames) {
			orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
		}
		sortPostProcessors(orderedPostProcessors, beanFactory);
		invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

		List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
		for (String postProcessorName : nonOrderedPostProcessorNames) {
			nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
		}
		invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
		beanFactory.clearMetadataCache();
	}

来看最上面定义

Set<String> processedBeans = new HashSet<>();

这个也很好理解,存放已经执行完的BeanFactoryPostProcessor名字,防止重复执行

if (beanFactory instanceof BeanDefinitionRegistry) {
			BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;

			//存放直接实现BeanFactoryPostProcessor,处理过/找到的实现类
			List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();

			//存放直接实现BeanDefinitionRegistryPostProcessor,处理过/找到的实现类
			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);
				}
			}

来看第一个if判断,判断传入的BeanFactory是否是BeanDefinitionRegistry类型,大部分情况都是,我们先默认它一直为true

那么上面定义两个集合用来存放已经处理过的实现类

下面这个for循环只有通过api来设置的BeanFactoryPostProcessor才会有值,什么意思呢?看下面

AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(Myconfig.class);context.addBeanFactoryPostProcessor(new MyBeanFactoryPostProcessor());

为什么没有呢?因为我们的代码运行顺序的问题,来看上面的使用代码,是先new AnnotationConfigApplicationContext(MyConfig.class)

而在它的构造中就已经调用refresh->invokeBeanFactoryPostProcessors->invokeBeanFactoryPostProcessors方法了

而我们debug时候还没有走到context.addBeanFactoryPostProcessor(new MyBeanFactoryPostProcessor());方法,所以为空

那怎么使用?我们仔细来看AnnotationConfigApplicationContext的构造

public AnnotationConfigApplicationContext(Class<?>... componentClasses) {    this();    register(componentClasses);    refresh();}

里面就3个方法,调自己无参,register,refresh,而执行invokeBeanFactoryPostProcessors在refresh方法中,也就是说我们可以在refresh方法前进行注册即可

AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();context.register(Myconfig.class);context.addBeanFactoryPostProcessor(new MyBeanFactoryPostProcessor());context.refresh();

这样,我们就能在refresh方法前进行手动调用api的方式添加

继续往下

if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {    BeanDefinitionRegistryPostProcessor registryProcessor =        (BeanDefinitionRegistryPostProcessor) postProcessor;    registryProcessor.postProcessBeanDefinitionRegistry(registry);    registryProcessors.add(registryProcessor);} else {    regularPostProcessors.add(postProcessor);}

判断是BeanDefinitionRegistryPostProcessor类型,如果是,则直接执行.否则添加到集合,还记得这个集合吗在最外层的if中

if (beanFactory instanceof BeanDefinitionRegistry) {    BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;    //存放直接实现BeanFactoryPostProcessor,处理过/找到的实现类    List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();    //存放直接实现BeanDefinitionRegistryPostProcessor,处理过/找到的实现类    List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();    ......}

如果不是则添加到regularPostProcessors集合,为什么这个类型不执行因为和Spring的执行顺序有关,等到最后在说

从List currentRegistryProcessors = new ArrayList<>();创建这个集合开始向下看

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);currentRegistryProcessors.clear();

首先这个集合干啥的:用来存放当前需要执行的BeanDefinitionRegistryPostProcessor

存放需要执行的BeanDefinitionRegistryPostProcessor的好理解,那什么叫做当前的?? 提前说一下,这个集合是在下面复用的,当前的就是当前正在执行的BeanDefinitionRegistryPostProcessor类型是一类的,先往下看,一会再解释

首先它创建一个字符串数组来接收beanFactory.getBeanNamesForType的返回参数,简单说下这个方法的作用

从BeanDefinitionNames中寻找类型为传入类型的BeanDefinition的名称

调用链为:DefaultListableBeanFactory.getBeanNamesForType->DefaultListableBeanFactory.doGetBeanNamesForType,有兴趣可以自己去看看

那我们debug来看看获取到类型是BeanDefinitionRegistryPostProcessor的beanName都有谁

那么继续向下

if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) 检查传入的PostProcessorName的BenaDefinition是否符合PriorityOrdered.class,当然该方法的作用不止于此,我们现在只分析有关的

PriorityOrdered是一个排序的接口,它的父类是Ordered,谁的值越小越先调用,先简单了解下即可,不是本章重点

public interface PriorityOrdered extends Ordered {}public interface Ordered {	int HIGHEST_PRECEDENCE = Integer.MIN_VALUE;	int LOWEST_PRECEDENCE = Integer.MAX_VALUE;	int getOrder();}

留个疑问,这个BeanDefinition什么时候进来的?先继续看代码整体返回true进入判断

currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));

主要重点在getBean方法,以后有机会在单独写篇getBean的,简单理解为从Spring的容器中获取类,如果不存在则从BeanDefinitionMap中找到对应BeanDefinition,然后实例化返回

那么假设我们已经获取到了实例化后的java对象,它是谁呢?debug

请记住这个类 ConfigurationClassPostProcessor

之后将当前类的名称存放到已经处理过的set中,在该方法的最上面

//储存已经完成处理的BeanFactoryPostProcessor名字
Set<String> processedBeans = new HashSet<>();

之后调用排序方法,然后把已经处理过的BeanFactoryPostProcessor存放到List

//存放直接实现BeanDefinitionRegistryPostProcessor,处理过的实现类
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();

我们重点来看invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);方法

private static void invokeBeanDefinitionRegistryPostProcessors(    Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry) {    for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {        postProcessor.postProcessBeanDefinitionRegistry(registry);    }}

上面找到的ConfigurationClassPostProcessor是重中之重,Spring的扫描就是这个类中完成的,何以证明?Debug

我们来看beanFactory中的BeanDefinitionMap数量即可

关于Spring的扫描以后有机会写一篇

然后清空当前正在执行的List集合,继续向下

postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);for (String ppName : postProcessorNames) {    //这里判断如果在存储已经完成的集合中没有找到当前的BeanDefinitionRegistryPostProcessor    //也就是说明这个还没有被执行过,那么放入当前执行的集合中进行下一步操作    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);//一样的代码,执行postProcessBeanFactory方法invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);currentRegistryProcessors.clear();

发现了什么,代码和上面的很像,那么我们不在赘述,直接简单说一下重点

if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class))

判断除了已经处理过的,防止重复执行,然后就是判断类型,上面的类型是PriorityOrdered 现在是Ordered

那么再来看

 currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));

而这个集合就是刚才定义的存放"当前处理"的集合

List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

什么叫当前处理,在最开始执行的时候,这个集合存放的都是实现PriorityOrdered接口的类,对于上面来说,"当前处理的"就是实现PriotyOrdered类,然后代码执行到currentRegistryProcessors.clear();那么对于实现PriorityOrdered接口的类来说,"当前处理"的这个集合,已经不是存放PriorityOrdered接口的实现类了

而到了这里,这个list中只存放Ordered类型的,那么"当前处理的"就指的是实现Ordered接口的类,因为它这个集合是好多地方复用的,所以叫做"当前处理"集合

那么下面的代码应该能看明白吧,上面处理了实现PriorityOrdered,Ordered的BeanDefinitionRegistryPostProcessor,都执行完了最后执行没有实现两者的BeanDefinitionRegistryPostProcessor

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);    currentRegistryProcessors.clear();}

那么这里可能有个疑问

registryProcessors.addAll(currentRegistryProcessors);invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);

这不是执行过了吗,为啥还要放集合,请注意,当前找的接口是BeanDefinitionRegistryPostProcessor的实现类,而不是BeanFactoryPostProcessor,那么一个简单的java基础问题,一个类实现了A接口,而A接口又继承B接口,请问这个类需要实现B接口定义的方法吗,答案是肯定的,那么上面的只是执行BeanDefinitionRegistryPostProcessor接口中定义的方法,所以来看后两行就一目了然了

//为什么要传入已经执行过的BeanDefinitionRegisterPostProcess的集合?
//因为我们自定义的类实现了BeanDefinitionRegisterPostProcess这个接口
//而这个接口又继承了BeanFactoryPostProcess,那么我们不仅要实现子类的方法,还要实现父类的方法
//而在上面的处理仅仅调用了子类的方法,所以又在这里调用一次父类的方法
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);

好的,到此为止,使用Api添加的PostProcessor完成,但是有个小问题,发现了吗,每次postProcessorNames都是重新获取一次,为什么不获取一次然后一直使用呢?

回过头我们来看开始使用BeanDefinitionRegistryPostProcessor的简单使用案例,假设实现PriorityOrdered接口的类在调用完postProcessBeanDefinitionRegistry方法对bean的数量进行了修改,那么下面的操作获取的数据都不是最新的,为了解决这个问题所以每次操作都重新获取一遍

继续向下走,下面的代码就是我们通过扫描或xml找到的BeanFactoryPostProcessor实现类

String[] postProcessorNames =    beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,// Ordered, and the rest.//分别是存放实现了priorityOrdered接口,Ordered接口,和没有实现Ordered接口的名称集合List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();List<String> orderedPostProcessorNames = new ArrayList<>();List<String> nonOrderedPostProcessorNames = new ArrayList<>();for (String ppName : postProcessorNames) {    if (processedBeans.contains(ppName)) {        // skip - already processed in first phase above    } 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);    }}// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.sortPostProcessors(priorityOrderedPostProcessors, beanFactory);invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);// Next, invoke the BeanFactoryPostProcessors that implement Ordered.List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();for (String postProcessorName : orderedPostProcessorNames) {    orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));}sortPostProcessors(orderedPostProcessors, beanFactory);invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);// Finally, invoke all other BeanFactoryPostProcessors.List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();for (String postProcessorName : nonOrderedPostProcessorNames) {    nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));}invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

下面的代码就比较简单了,就简单写下

首先还是通过 beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);获取类型为BeanFactoryPostProcessor的实现类名称,然后依次判断实现了PriorityOrdered接口了吗,实现Ordered接口了吗,还是两个都没实现

分别放到对应的集合中,随后顺序执行

我们来捋一下执行的顺序

通过Api添加实现BeanDefinitionRegistryPostProcessor的类
Spring内置
1. 实现PriorityOrdered接口
2. 实现Ordered接口
3. 两者都没实现
通过Api添加实现BeanFactoryPostProcessor的类
执行通过扫描/xml配置实现BeanFactoryPostProcessor和PriorityOrdered的类
执行通过扫描/xml配置实现BeanFactoryPostProcessor和Ordered的类
执行通过扫描/xml配置实现BeanFactoryPostProcessor的类

我们来写代码实际演示下

整体结构如下

@Component
public class BDPP implements BeanFactoryPostProcessor {

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("俺啥排序接口都没实现");
    }
}


@Component
public class BDPPOrdered0 implements Ordered, BeanFactoryPostProcessor {
    @Override
    public int getOrder() {return 0;}
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("实现Ordered的BDPP,排序0");
    }
}

@Component
public class BDPPOrdered1 implements Ordered, BeanFactoryPostProcessor {
    @Override
    public int getOrder() {return 1;}
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("实现Ordered的BDPP,排序1");
    }
}


@Component
public class BDPPPriorityOrdered0 implements PriorityOrdered, BeanFactoryPostProcessor {
    @Override
    public int getOrder() {return 0;}
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("实现PriorityOrdered的BDPP,排序0");
    }
}

@Component
public class BDPPPriorityOrdered1 implements PriorityOrdered, BeanFactoryPostProcessor {
    @Override
    public int getOrder() {return 1;}

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("实现PriorityOrdered的BDPP,排序1");
    }
}


public class MyBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        System.out.println("Api添加的BeanDefinitionRegistryPostProcessor,我是该接口的方法");
    }
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("Api添加的BeanDefinitionRegistryPostProcessor,我是父接口方法");
    }
}


public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("Api添加的BeanFactoryPostProcessor");
    }
}


public static void main(String[] args) {
    AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
    context.register(Myconfig.class);
    context.addBeanFactoryPostProcessor(new MyBeanFactoryPostProcessor());
    context.addBeanFactoryPostProcessor(new MyBeanDefinitionRegistryPostProcessor());
    context.refresh();
}

在Spring扫描的方法中添加一句话用于输出

其他Spring内置的就不再去添加了,我们来看结果

也就是说如果想在Spring完成扫描前对Bean进行一些操作可以实现BeanDefinitionRegistryPostProcessor接口并手动添加,而上面的输出也显示了,在同继承PriorityOrdered或Ordered的时候,值小的先执行

还有一个问题,我们在获取BeanFactoryPostProcessor时名称使用前每次都是重新获取一下,而在下面通过扫描或Xml配置的BeanFactoryPostProcessor时却只进行一次获取

String[] postProcessorNames =    beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

因为BeanFactoryPostProcessor接口只是对bean进行增强处理,不会进行删除新增的操作

回答上面的疑问:这个ConfigurationClassPostProcessor的BeanDefinition什么时候进来的

来看new AnnotationConfigApplicationContext()的无参构造

public AnnotationConfigApplicationContext() {
    //spring内置的bd将在这里进行注册
    this.reader = new AnnotatedBeanDefinitionReader(this);
    this.scanner = new ClassPathBeanDefinitionScanner(this);
}

public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {
    Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
    Assert.notNull(environment, "Environment must not be null");
    this.registry = registry;
    this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
    //这里
    AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}

public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
    BeanDefinitionRegistry registry, @Nullable Object source) {
    .....
        if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
            def.setSource(source);
            beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
        }
    .......
}

还记得上面第一次通过String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);

来看CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME这个常量的值是啥

public static final String CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME =
    "org.springframework.context.annotation.internalConfigurationAnnotationProcessor";

而它这个if判断是

@Override
public boolean containsBeanDefinition(String beanName) {
    Assert.notNull(beanName, "Bean name must not be null");
    return this.beanDefinitionMap.containsKey(beanName);
}

也就是说在初始化时,如果不存在则进行注册beanDefinition,具体注册的方法从

beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));

registry.registerBeanDefinition(beanName, definition);

DefaultListableBeanFactory.registerBeanDefinition注册beanDefinition的方法,有兴趣可以点进去看看

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