Spring笔记(6) - Spring的BeanFactoryPostProcessor探究

一.背景

　　在说BeanFactoryPostProcessor之前，先来说下BeanPostProcessor，在前文Spring笔记(2) - 生命周期/属性赋值/自动装配及部分源码解析中讲解了BeanPostProcessor是一个bean后置处理器（bean创建对象初始化前后进行拦截工作）。

　　BeanPostProcessor的运行流程如下：

　　　　1）Spring IOC容器实例化Bean；

　　　　2）调用BeanPostProcessor的postProcessBeforeInitialization方法；

　　　　3）调用bean实例的初始化方法；

　　　　4）调用BeanPostProcessor的postProcessAfterInitialization方法；

　　实现BeanPostProcessor接口可以在Bean(实例化之后)初始化的前后做一些自定义的操作，但是拿到的参数只有BeanDefinition实例和BeanDefinition的名称，也就是无法修改BeanDefinition元数据,这里说的Bean的初始化是：

　　　　1）bean实现了InitializingBean接口，对应的方法为afterPropertiesSet

　　　　2）在bean定义的时候，通过init-method设置的方法

　　Spring中Bean的实例化过程图示：　　

　　那么BeanFactoryPostProcessor顾名思义就是bean工厂的后置处理器，说通俗一些就是可以管理我们的bean工厂内所有的BeanDefinition（未实例化）数据，可以随心所欲的修改属性。　　　　　　　　　　　　

　　Spring容器初始化时，从资源中读取到bean的相关定义后，保存在beanFactory的成员变量中（参考DefaultListableBeanFactory类的成员变量beanDefinitionMap），在实例化bean的操作就是依据这些bean的定义来做的，而在实例化之前，Spring允许我们通过自定义扩展来改变bean的定义，定义一旦变了，后面的实例也就变了，而beanFactory后置处理器，即BeanFactoryPostProcessor就是用来改变bean定义的；如果业务需要，可以配置多个BeanFactoryPostProcessor的实现类，通过”order”控制执行次序(要实现Ordered接口)。

　　注册一个BeanFactoryPostProcessor实例需要定义一个Java类来实现BeanFactoryPostProcessor接口，并重写该接口的postProcessorBeanFactory方法。通过beanFactory可以获取bean的定义信息，并可以修改bean的定义信息。（这点是和BeanPostProcessor最大区别）

　　所以通过上面的介绍可以总结出有两种方式可以对bean做控制（例如修改某个成员变量）：

　　　　1. 只改变实例化的对象(BeanPostProcessor接口)；

　　　　2. 改变bean的定义(BeanFactoryPostProcessor接口) ，可以想象成修改了class文件，这样实例化出来的每个对象都变了；　　

　　PS：BeanFactoryPostProcessor回调会先于BeanPostProcessor　　

　　下面是BeanFactoryPostProcessor的源码：

public interface BeanFactoryPostProcessor {

    /**
     * Modify the application context's internal bean factory after its standard
     * initialization. All bean definitions will have been loaded, but no beans
     * will have been instantiated yet. This allows for overriding or adding
     * properties even to eager-initializing beans.
     * @param beanFactory the bean factory used by the application context
     * @throws org.springframework.beans.BeansException in case of errors
     */
     //在ioc容器的bean Factory标准初始化之后可以对它们进行修改。所有的bean定义被加载了，但还没有被实例化。
     //允许进行重载或添加属性即使在eager-initializing beans
    void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

}

　　BeanFactoryPostProcessor此接口只提供了一个方法，方法参数为ConfigurableListableBeanFactory，下面是该类的源码：

public interface ConfigurableListableBeanFactory
        extends ListableBeanFactory, AutowireCapableBeanFactory, ConfigurableBeanFactory {

    void ignoreDependencyType(Class<?> type);

    void ignoreDependencyInterface(Class<?> ifc);

    void registerResolvableDependency(Class<?> dependencyType, @Nullable Object autowiredValue);

    boolean isAutowireCandidate(String beanName, DependencyDescriptor descriptor)
            throws NoSuchBeanDefinitionException;

    BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;

    Iterator<String> getBeanNamesIterator();

    void clearMetadataCache();

    void freezeConfiguration();

    boolean isConfigurationFrozen();

    void preInstantiateSingletons() throws BeansException;

}

　　其中有个方法名为getBeanDefinition的方法，我们可以根据此方法，找到我们定义bean的BeanDefinition对象。然后我们可以对定义的属性进行修改，以下是BeanDefinition中的方法：

public interface BeanDefinition extends AttributeAccessor, BeanMetadataElement {

    /**
     * Scope identifier for the standard singleton scope: "singleton".
     * <p>Note that extended bean factories might support further scopes.
     * @see #setScope
     */
    String SCOPE_SINGLETON = ConfigurableBeanFactory.SCOPE_SINGLETON;

    /**
     * Scope identifier for the standard prototype scope: "prototype".
     * <p>Note that extended bean factories might support further scopes.
     * @see #setScope
     */
    String SCOPE_PROTOTYPE = ConfigurableBeanFactory.SCOPE_PROTOTYPE;

    /**
     * Role hint indicating that a {@code BeanDefinition} is a major part
     * of the application. Typically corresponds to a user-defined bean.
     */
    int ROLE_APPLICATION = 0;

    /**
     * Role hint indicating that a {@code BeanDefinition} is a supporting
     * part of some larger configuration, typically an outer
     * {@link org.springframework.beans.factory.parsing.ComponentDefinition}.
     * {@code SUPPORT} beans are considered important enough to be aware
     * of when looking more closely at a particular
     * {@link org.springframework.beans.factory.parsing.ComponentDefinition},
     * but not when looking at the overall configuration of an application.
     */
    int ROLE_SUPPORT = 1;

    /**
     * Role hint indicating that a {@code BeanDefinition} is providing an
     * entirely background role and has no relevance to the end-user. This hint is
     * used when registering beans that are completely part of the internal workings
     * of a {@link org.springframework.beans.factory.parsing.ComponentDefinition}.
     */
    int ROLE_INFRASTRUCTURE = 2;

    // Modifiable attributes

    /**
     * Set the name of the parent definition of this bean definition, if any.
     */
    void setParentName(@Nullable String parentName);

    /**
     * Return the name of the parent definition of this bean definition, if any.
     */
    @Nullable
    String getParentName();

    /**
     * Specify the bean class name of this bean definition.
     * <p>The class name can be modified during bean factory post-processing,
     * typically replacing the original class name with a parsed variant of it.
     * @see #setParentName
     * @see #setFactoryBeanName
     * @see #setFactoryMethodName
     */
    void setBeanClassName(@Nullable String beanClassName);

    /**
     * Return the current bean class name of this bean definition.
     * <p>Note that this does not have to be the actual class name used at runtime, in
     * case of a child definition overriding/inheriting the class name from its parent.
     * Also, this may just be the class that a factory method is called on, or it may
     * even be empty in case of a factory bean reference that a method is called on.
     * Hence, do <i>not</i> consider this to be the definitive bean type at runtime but
     * rather only use it for parsing purposes at the individual bean definition level.
     * @see #getParentName()
     * @see #getFactoryBeanName()
     * @see #getFactoryMethodName()
     */
    @Nullable
    String getBeanClassName();

    /**
     * Override the target scope of this bean, specifying a new scope name.
     * @see #SCOPE_SINGLETON
     * @see #SCOPE_PROTOTYPE
     */
    void setScope(@Nullable String scope);

    /**
     * Return the name of the current target scope for this bean,
     * or {@code null} if not known yet.
     */
    @Nullable
    String getScope();

    /**
     * Set whether this bean should be lazily initialized.
     * <p>If {@code false}, the bean will get instantiated on startup by bean
     * factories that perform eager initialization of singletons.
     */
    void setLazyInit(boolean lazyInit);

    /**
     * Return whether this bean should be lazily initialized, i.e. not
     * eagerly instantiated on startup. Only applicable to a singleton bean.
     */
    boolean isLazyInit();

    /**
     * Set the names of the beans that this bean depends on being initialized.
     * The bean factory will guarantee that these beans get initialized first.
     */
    void setDependsOn(@Nullable String... dependsOn);

    /**
     * Return the bean names that this bean depends on.
     */
    @Nullable
    String[] getDependsOn();

    /**
     * Set whether this bean is a candidate for getting autowired into some other bean.
     * <p>Note that this flag is designed to only affect type-based autowiring.
     * It does not affect explicit references by name, which will get resolved even
     * if the specified bean is not marked as an autowire candidate. As a consequence,
     * autowiring by name will nevertheless inject a bean if the name matches.
     */
    void setAutowireCandidate(boolean autowireCandidate);

    /**
     * Return whether this bean is a candidate for getting autowired into some other bean.
     */
    boolean isAutowireCandidate();

    /**
     * Set whether this bean is a primary autowire candidate.
     * <p>If this value is {@code true} for exactly one bean among multiple
     * matching candidates, it will serve as a tie-breaker.
     */
    void setPrimary(boolean primary);

    /**
     * Return whether this bean is a primary autowire candidate.
     */
    boolean isPrimary();

    /**
     * Specify the factory bean to use, if any.
     * This the name of the bean to call the specified factory method on.
     * @see #setFactoryMethodName
     */
    void setFactoryBeanName(@Nullable String factoryBeanName);

    /**
     * Return the factory bean name, if any.
     */
    @Nullable
    String getFactoryBeanName();

    /**
     * Specify a factory method, if any. This method will be invoked with
     * constructor arguments, or with no arguments if none are specified.
     * The method will be invoked on the specified factory bean, if any,
     * or otherwise as a static method on the local bean class.
     * @see #setFactoryBeanName
     * @see #setBeanClassName
     */
    void setFactoryMethodName(@Nullable String factoryMethodName);

    /**
     * Return a factory method, if any.
     */
    @Nullable
    String getFactoryMethodName();

    /**
     * Return the constructor argument values for this bean.
     * <p>The returned instance can be modified during bean factory post-processing.
     * @return the ConstructorArgumentValues object (never {@code null})
     */
    ConstructorArgumentValues getConstructorArgumentValues();

    /**
     * Return if there are constructor argument values defined for this bean.
     * @since 5.0.2
     */
    default boolean hasConstructorArgumentValues() {
        return !getConstructorArgumentValues().isEmpty();
    }

    /**
     * Return the property values to be applied to a new instance of the bean.
     * <p>The returned instance can be modified during bean factory post-processing.
     * @return the MutablePropertyValues object (never {@code null})
     */
    MutablePropertyValues getPropertyValues();

    /**
     * Return if there are property values values defined for this bean.
     * @since 5.0.2
     */
    default boolean hasPropertyValues() {
        return !getPropertyValues().isEmpty();
    }

    /**
     * Set the name of the initializer method.
     * @since 5.1
     */
    void setInitMethodName(@Nullable String initMethodName);

    /**
     * Return the name of the initializer method.
     * @since 5.1
     */
    @Nullable
    String getInitMethodName();

    /**
     * Set the name of the destroy method.
     * @since 5.1
     */
    void setDestroyMethodName(@Nullable String destroyMethodName);

    /**
     * Return the name of the destroy method.
     * @since 5.1
     */
    @Nullable
    String getDestroyMethodName();

    /**
     * Set the role hint for this {@code BeanDefinition}. The role hint
     * provides the frameworks as well as tools with an indication of
     * the role and importance of a particular {@code BeanDefinition}.
     * @since 5.1
     * @see #ROLE_APPLICATION
     * @see #ROLE_SUPPORT
     * @see #ROLE_INFRASTRUCTURE
     */
    void setRole(int role);

    /**
     * Get the role hint for this {@code BeanDefinition}. The role hint
     * provides the frameworks as well as tools with an indication of
     * the role and importance of a particular {@code BeanDefinition}.
     * @see #ROLE_APPLICATION
     * @see #ROLE_SUPPORT
     * @see #ROLE_INFRASTRUCTURE
     */
    int getRole();

    /**
     * Set a human-readable description of this bean definition.
     * @since 5.1
     */
    void setDescription(@Nullable String description);

    /**
     * Return a human-readable description of this bean definition.
     */
    @Nullable
    String getDescription();

    // Read-only attributes

    /**
     * Return a resolvable type for this bean definition,
     * based on the bean class or other specific metadata.
     * <p>This is typically fully resolved on a runtime-merged bean definition
     * but not necessarily on a configuration-time definition instance.
     * @return the resolvable type (potentially {@link ResolvableType#NONE})
     * @since 5.2
     * @see ConfigurableBeanFactory#getMergedBeanDefinition
     */
    ResolvableType getResolvableType();

    /**
     * Return whether this a <b>Singleton</b>, with a single, shared instance
     * returned on all calls.
     * @see #SCOPE_SINGLETON
     */
    boolean isSingleton();

    /**
     * Return whether this a <b>Prototype</b>, with an independent instance
     * returned for each call.
     * @since 3.0
     * @see #SCOPE_PROTOTYPE
     */
    boolean isPrototype();

    /**
     * Return whether this bean is "abstract", that is, not meant to be instantiated.
     */
    boolean isAbstract();

    /**
     * Return a description of the resource that this bean definition
     * came from (for the purpose of showing context in case of errors).
     */
    @Nullable
    String getResourceDescription();

    /**
     * Return the originating BeanDefinition, or {@code null} if none.
     * Allows for retrieving the decorated bean definition, if any.
     * <p>Note that this method returns the immediate originator. Iterate through the
     * originator chain to find the original BeanDefinition as defined by the user.
     */
    @Nullable
    BeanDefinition getOriginatingBeanDefinition();

}

　　我们可以在上面代码中发现里面的方法名字类似bean标签的属性，setBeanClassName对应bean标签中的class属性，所以当我们拿到BeanDefinition对象时，我们可以手动修改bean标签中所定义的属性值。

　　具体这个BeanDefinition是个什么对象，当我们在xml中定义了bean标签时，Spring会把这些bean标签解析成一个javabean，这个BeanDefinition就是bean标签对应的javabean。

　　所以当我们调用BeanFactoryPostProcess方法时，这时候bean还没有实例化，此时bean刚被解析成BeanDefinition对象。

　　Spring容器初始化bean大致过程 ：

　　　　1）定义bean标签

　　　　2）将bean标签解析成BeanDefinition

　　　　3）调用构造方法实例化(IOC)

　　　　4）属性值得依赖注入(DI)

　　所以可以看出BeanFactoryPostProcess方法的执行是发生在第二步之后，第三步之前。

　　综上所述BeanPostProcessor和BeanFactoryPostProcess都是为Spring提供的后处理bean的接口，只是两者执行的时机不一样。BeanPostProcessor为实例化之后，BeanFactoryPostProcess是实例化之前。功能上，BeanFactoryPostProcess对bean的处理功能更加强大。

二.案例

　　1.配置类：进行包扫描将类加载到容器中

@ComponentScan("com.hrh.ext")
@Configuration
public class ExtConfig {
    @Bean
    public Person person() {
        return new Person("张三", "男");
    }
}

　　2.实体类：

public class Person implements InitializingBean, DisposableBean, BeanNameAware, BeanFactoryAware {
private String name;
private String sex;

    public Person() {
        System.out.println("Person无参构造器");

    }

    public Person(String name, String sex) {
        System.out.println("Person有参构造器:[name=" + name + ",sex=" + sex + "]");
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        System.out.println("[Person]调用了BeanFactoryAware的setBeanFactory方法了：" + beanFactory);
    }

    @Override
    public void setBeanName(String name) {
        System.out.println("[Person]调用了BeanNameAware的setBeanName方法了:" + name);
    }

    @Override
    public void destroy() throws Exception {
        System.out.println("[Person]调用了DisposableBean的destroy方法了");
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("[Person]调用了Initailization的afterPropertiesSet方法了");
    }

    @Override
    public String toString() {
        return "Person [name=" + name + ", sex=" + sex
                + "]";
    }
}

　　3.自定义BeanFactoryPostProcessor类：

@Component
public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("[MyBeanFactoryPostProcessor]调用了postProcessBeanFactory");
        int count = beanFactory.getBeanDefinitionCount();
        System.out.println("[MyBeanFactoryPostProcessor]当前beanFactory共有" + count + "个bean");
        String[] beanDefinitionNames = beanFactory.getBeanDefinitionNames();
        System.out.println("[MyBeanFactoryPostProcessor]当前beanFactory有下面组件" + Arrays.asList(beanDefinitionNames));
        //获取容器中所有的beanDefinition
        for (String beanName : beanDefinitionNames) {
            if ("person".equals(beanName)) {
                //获取PersonDefinition对象
                BeanDefinition beanDefinition = beanFactory.getBeanDefinition(beanName);
                MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();
                System.out.println(propertyValues.toString());
                //修改定义中的name属性值
                propertyValues.addPropertyValue("name", "赵四");
                System.out.println("[MyBeanFactoryPostProcessor]postProcessBeanFactory方法中修改了name属性初始值了");
                System.out.println(propertyValues.toString());
            }
        }
    }
}

　　4.自定义BeanPostProcessor类：

@Component
public class MyBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean,
                                                  String beanName) throws BeansException {
        System.out.println("[MyBeanPostProcessor]后置处理器处理bean=【" + beanName + "】开始");
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean,
                                                 String beanName) throws BeansException {
        System.out.println("[MyBeanPostProcessor]后置处理器处理bean=【" + beanName + "】完毕!");
        return bean;
    }
}

　　5.测试：

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(ExtConfig.class);
        Person bean = context.getBean(Person.class);
        System.out.println(bean.toString());
        context.close();
    }

======运行结果======
[MyBeanFactoryPostProcessor]调用了postProcessBeanFactory
[MyBeanFactoryPostProcessor]当前beanFactory共有9个bean
[MyBeanFactoryPostProcessor]当前beanFactory有下面组件[org.springframework.context.annotation.internalConfigurationAnnotationProcessor, org.springframework.context.annotation.internalAutowiredAnnotationProcessor, org.springframework.context.annotation.internalCommonAnnotationProcessor, org.springframework.context.event.internalEventListenerProcessor, org.springframework.context.event.internalEventListenerFactory, extConfig, myBeanFactoryPostProcessor, myBeanPostProcessor, person]
PropertyValues: length=0
[MyBeanFactoryPostProcessor]postProcessBeanFactory方法中修改了name属性初始值了
PropertyValues: length=1; bean property 'name'
[MyBeanPostProcessor]后置处理器处理bean=【extConfig】开始
[MyBeanPostProcessor]后置处理器处理bean=【extConfig】完毕!
Person有参构造器:[name=张三,sex=男]
[Person]调用了BeanNameAware的setBeanName方法了:person
[Person]调用了BeanFactoryAware的setBeanFactory方法了：org.springframework.beans.factory.support.DefaultListableBeanFactory@e45f292: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.event.internalEventListenerProcessor,org.springframework.context.event.internalEventListenerFactory,extConfig,myBeanFactoryPostProcessor,myBeanPostProcessor,person]; root of factory hierarchy
[MyBeanPostProcessor]后置处理器处理bean=【person】开始
[Person]调用了Initailization的afterPropertiesSet方法了
[MyBeanPostProcessor]后置处理器处理bean=【person】完毕!
Person [name=赵四, sex=null]
[Person]调用了DisposableBean的destroy方法了

　　从上面的运行结果可以看出：

　　　　1）Person的name值由"张三"变为"赵四"；

　　　　2）BeanFactoryPostProcessor方法执行顺序先于BeanPostProcessor接口中方法，且在bean实例化之前执行；

　　　　3）BeanFactoryPostProcessor改变bean的定义，实例化出来的对象变了：“Person有参构造器:[name=张三,sex=男] ”变成了“Person [name=赵四, sex=null]”

　　　　4）BeanPostProcessor在bean创建对象实例化后，初始化（bean执行afterPropertiesSet方法或init-method方法）前后进行拦截工作；

三.原理

　　接下来我们通过debug代码来查看BeanFactoryPostProcessor的执行流程，从AbstractApplicationContext类的构造器方法看起，这里面对应着容器初始化的基本操作；

　　1.在测试main方法中下面的代码打断点：

AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(ExtConfig.class);

　　2.从下图可以看出容器先注册配置类ExtConfig的定义信息，然后进行refresh刷新容器；

　　3.先来看看register(componentClasses)注册流程：从class文件读取信息解析成beanDefinition

AnnotationConfigApplicationContext：
    public void register(Class<?>... componentClasses) {
        Assert.notEmpty(componentClasses, "At least one component class must be specified");
        this.reader.register(componentClasses);
    }

AnnotatedBeanDefinitionReader：注册beanDefinition
    public void register(Class<?>... componentClasses) {
        for (Class<?> componentClass : componentClasses) {
            registerBean(componentClass);
        }
    }

    public void registerBean(Class<?> beanClass) {
        doRegisterBean(beanClass, null, null, null, null);
    }

    //Register a bean from the given bean class, deriving its metadata from  class-declared annotations.
    //从class文件中读取bean的定义信息，并注册到容器中
    private <T> void doRegisterBean(Class<T> beanClass, @Nullable String name,
        @Nullable Class<? extends Annotation>[] qualifiers, @Nullable Supplier<T> supplier,
        @Nullable BeanDefinitionCustomizer[] customizers) {
        //得到bean的所有定义信息：元数据metadata、作用域scope、初始化方法名字initMethodName等等
        AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(beanClass);
        if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
            return;
        }
        //为bean实例创建一个特殊的回调信号
        abd.setInstanceSupplier(supplier);
        //获取作用域的数据：单例
        ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
        //设置bean为单例
        abd.setScope(scopeMetadata.getScopeName());
        //获取beanName
        String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
        //处理一些注释信息：lazyInit、primary、dependsOn、role、description
        AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
        if (qualifiers != null) {//qualifiers = nul 跳过
            for (Class<? extends Annotation> qualifier : qualifiers) {
                if (Primary.class == qualifier) {
                    abd.setPrimary(true);
                }
                else if (Lazy.class == qualifier) {
                    abd.setLazyInit(true);
                }
                else {
                    abd.addQualifier(new AutowireCandidateQualifier(qualifier));
                }
            }
        }
        if (customizers != null) {//customizers = null跳过
            for (BeanDefinitionCustomizer customizer : customizers) {
                customizer.customize(abd);
            }
        }
        //创建一个BeanDefinitionHolder
        BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
        definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
        //容器中注册beanDefinition
        BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
    }

　　4.refresh刷新容器：invokeBeanFactoryPostProcessors方法用来找出所有beanFactory后置处理器，并且调用这些处理器来改变bean的定义

    public void refresh() throws BeansException, IllegalStateException {
        //来个锁，不然 refresh() 还没结束，你又来个启动或销毁容器的操作，那不就乱套了嘛
        synchronized (this.startupShutdownMonitor) {
            // Prepare this context for refreshing.
            //容器刷新前的处理方法：获取启动的系统时间、设置active活跃标识、开始打印日志、设置环境变量、设置容器监听器、设置容器事件
            prepareRefresh();

            // Tell the subclass to refresh the internal bean factory.
            //刷新bean工厂并获取到bean工厂
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // Prepare the bean factory for use in this context.
            // bean工厂的初始化操作：设置类加载器、设置bean表达式解析器、设置bean后置处理器等等；
            prepareBeanFactory(beanFactory);

            try {
                // Allows post-processing of the bean factory in context subclasses.
                // 【这里需要知道 BeanFactoryPostProcessor 这个知识点，Bean 如果实现了此接口，
                // 那么在容器初始化以后，Spring 会负责调用里面的 postProcessBeanFactory 方法。】
                 // 这里是提供给子类的扩展点，到这里的时候，所有的 Bean 都加载、注册完成了，但是都还没有初始化
                 // 具体的子类可以在这步的时候根据自身业务添加或修改一些特殊的 beanFactory属性
                postProcessBeanFactory(beanFactory);

                // Invoke factory processors registered as beans in the context.
                //找出所有beanFactory后置处理器，并且调用这些处理器来改变bean的定义
                invokeBeanFactoryPostProcessors(beanFactory);

                // Register bean processors that intercept bean creation.
                //注册bean后置处理器
                registerBeanPostProcessors(beanFactory);

                // Initialize message source for this context.
                //初始化容器的信息源
                initMessageSource();

                // Initialize event multicaster for this context.
                //初始化事件监听多路广播器
                initApplicationEventMulticaster();

                // Initialize other special beans in specific context subclasses.
                //是个空壳方法，在AnnotationApplicationContex上下文中没有实现，可能在spring后面的版本会去扩展。
                //与Web上下文有关
                onRefresh();

                // Check for listener beans and register them.
                //注册监听器
                registerListeners();

                // Instantiate all remaining (non-lazy-init) singletons.
                //对象的创建:初始化剩下所有的(非懒加载的）单实例对象【从这里可以看出beanFactory后置处理器在初始化其他组件之前执行】
                finishBeanFactoryInitialization(beanFactory);

                // Last step: publish corresponding event.
                //刷新完成工作，包括初始化LifecycleProcessor，发布刷新完成事件等
                finishRefresh();
            }

            catch (BeansException ex) {
                if (logger.isWarnEnabled()) {
                    logger.warn("Exception encountered during context initialization - " +
                            "cancelling refresh attempt: " + ex);
                }

                // Destroy already created singletons to avoid dangling resources.
                //销毁已经初始化的 singleton 的 Beans，以免有些 bean 会一直占用资源
                destroyBeans();

                // Reset 'active' flag.
                //取消刷新的标志
                cancelRefresh(ex);

                // Propagate exception to caller.
                throw ex;
            }

            finally {
                // Reset common introspection caches in Spring's core, since we
                // might not ever need metadata for singleton beans anymore...
                resetCommonCaches();
            }
        }
    }

　　5.打开invokeBeanFactoryPostProcessors方法，如下所示，实际操作是委托PostProcessorRegis

trationDelegate去完成的：调用getBeanFactoryPostProcessors()方法获取手工注册到ApplicationCon

text的容器后置处理器集合

    protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

        // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
        // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
        if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }
    } 

　　1）在调用PostProcessorRegistrationDelegate类的invokeBeanFactoryPostProcessors方法时，注意第二个入参是getBeanFactoryPostProcessors()方法，该方法返回的是applicationContext的成员变量beanFactoryPostProcessors，该成员变量的值来自AbstractApplicationContext.addBeanFactoryPostProcessor方法被调用的时候：

    private final List<BeanFactoryPostProcessor> beanFactoryPostProcessors = new ArrayList<>();
    @Override
    public void addBeanFactoryPostProcessor(BeanFactoryPostProcessor postProcessor) {
        Assert.notNull(postProcessor, "BeanFactoryPostProcessor must not be null");
        this.beanFactoryPostProcessors.add(postProcessor);
    }

    public List<BeanFactoryPostProcessor> getBeanFactoryPostProcessors() {
        return this.beanFactoryPostProcessors;
    }

　　　　2）AbstractApplicationContext.addBeanFactoryPostProcessor方法是留给业务扩展时调用的，例如在springboot初始化时，ConfigurationWarningsApplicationContextInitializer类的initialize方法中就有调用：

@Override
public void initialize(ConfigurableApplicationContext context) {
    context.addBeanFactoryPostProcessor(
            new ConfigurationWarningsPostProcessor(getChecks()));
}

6.看过了如何添加BeanFactoryPostProcessor，再回到PostProcessorRegistrationDelegate.invok

eBeanFactoryPostProcessors方法：实例化并调用所有已注册的BeanFactoryPostProcessor bean；

流程是：

　　1）beanFactory是BeanDefinitionRegistry类型时，此条件下完成如下流程：

　　　　1.遍历传入后置处理器集合查找类型为BeanDefinitionRegistryPostProcessor的后置处理器，调用后置处理器的postProcessBeanDefinitionRegistry方法；

　　　　2.在容器中查找所有的实现了PriorityOrdered接口的BeanDefinition

RegistryPostProcessor集合，对后置处理器集合排序，遍历，执行后置处理的postProcessBeanDefinitionRegistry方法；

　　　　3.在容器中查找所有实现了Ordered接口的BeanDefinitionRegistryPostProcessor集合，对后置处理器集合排序，遍历，执行后置处理的postProcessBeanDefinitionRegistry方法；

　　　　4.在容器中查找其它（未实现排序接口）的BeanDefinitionRegistryPostProcessor并添加到集合nonOrderedPostProcessors中，对后置处理器集合排序，遍历，执行后置处理的postProcessBeanDefinitionRegistry方法；

　　　　5.当前所有的BeanDefinitionRegistryPostProcessor处理器的方法postProcessBeanD

efinitionRegistry 执行完毕后，执行其父类postProcessBeanFactory方法；

　　　　6.执行所有非BeanDefinitionRegistryPostProcessor类型的后置处理器的postProcessB

eanFactory方法；

　　2）beanFactory非BeanDefinitionRegistry类型时，此条件下完成如下流程：

　　　　1.遍历传入后置处理器集合，执行后置处理器的postProcessBeanFactory方法；

　　　　2.在容器中（beanFactory.getBeanNamesForType）查找所有的实现了PriorityOrdered接口的BeanFactoryPostProcessor集合，对后置处理器集合排序，遍历，执行后置处理；

　　　　3.在容器中查找所有实现了Ordered接口的BeanFactoryPostProcessor集合，对后置处理器集合排序，遍历，执行后置处理；

　　　　4.在容器中查找其它（未实现排序接口）的BeanFactoryPostProcessor并添加到集合nonOrderedPostProcessors中，对后置处理器集合排序，遍历，执行后置处理；

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

        // Invoke BeanDefinitionRegistryPostProcessors first, if any.
        Set<String> processedBeans = new HashSet<>();
        //如果beanFactory实现了BeanDefinitionRegistry
        if (beanFactory instanceof BeanDefinitionRegistry) {
            BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
            List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
            List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();

            for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
                //如果beanFactoryPostProcessor实现了BeanDefinitionRegistryPostProcessor，分别放入两个集合：registryProcessors 和 regularPostProcessors
                if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                    BeanDefinitionRegistryPostProcessor registryProcessor =
                            (BeanDefinitionRegistryPostProcessor) postProcessor;
                    registryProcessor.postProcessBeanDefinitionRegistry(registry);
                    registryProcessors.add(registryProcessor);
                }
                else {
                    regularPostProcessors.add(postProcessor);
                }
            }

            // Do not initialize FactoryBeans here: We need to leave all regular beans
            // uninitialized to let the bean factory post-processors apply to them!
            // Separate between BeanDefinitionRegistryPostProcessors that implement
            // PriorityOrdered, Ordered, and the rest.
            List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

            // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
            //找出所有实现了BeanDefinitionRegistryPostProcessor接口和PriorityOrdered接口的bean，放入registryProcessors集合，
            //放入根据Set接口来排序，然后这些bean会被invokeBeanDefinitionRegistryPostProcessors方法执行；
            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();

            // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
            //找出所有实现了BeanDefinitionRegistryPostProcessor接口和Ordered接口的bean，放入registryProcessors集合，
            //放入根据Set接口来排序，然后这些bean会被invokeBeanDefinitionRegistryPostProcessors方法执行；
            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();

            // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
            //对于那些实现了BeanDefinitionRegistryPostProcessor接口，但是没有实现PriorityOrdered和Ordered的bean也被找出来，
            //然后这些bean会被invokeBeanDefinitionRegistryPostProcessors方法执行；
            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();
            }

            // Now, invoke the postProcessBeanFactory callback of all processors handled so far.
            //registryProcessors和regularPostProcessors集合被invokeBeanFactoryPostProcessors执行
            invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
            invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
        }

        else {
            // Invoke factory processors registered with the context instance.
            //入参中的BeanFactoryPostProcessor，没有实现BeanDefinitionRegistryPostProcessor的那些bean，被invokeBeanFactoryPostProcessors执行
            invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
        }

        // Do not initialize FactoryBeans here: We need to leave all regular beans
        // uninitialized to let the bean factory post-processors apply to them!
        String[] postProcessorNames =
                beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

        // Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
        // Ordered, and the rest.
        //找出实现了BeanFactoryPostProcessor接口的bean，注意这里已将上面实现了BeanDefinitionRegistryPostProcessor接口的bean给剔除了，
        //将这些bean分为三类：实现了PriorityOrdered接口的放入priorityOrderedPostProcessors，
        //实现了Ordered接口的放入orderedPostProcessorNames，其他的放入nonOrderedPostProcessorNames
        //自定义的实现BeanFactoryPostProcessor接口的bean就会在nonOrderedPostProcessorNames被找出来
        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.
        //priorityOrderedPostProcessors先排序再被invokeBeanFactoryPostProcessors执行
        sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
        invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

        // Next, invoke the BeanFactoryPostProcessors that implement Ordered.
        //orderedPostProcessorNames先被遍历加入到orderedPostProcessors，再被排序，最后才被invokeBeanFactoryPostProcessors执行
        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.
        //nonOrderedPostProcessorNames也是先被遍历到nonOrderedPostProcessors，再被invokeBeanFactoryPostProcessors执行
        List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
        for (String postProcessorName : nonOrderedPostProcessorNames) {
            nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        //这时才是执行自定义BeanFactoryPostProcessor的postProcessBeanFactory
        invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

        // Clear cached merged bean definitions since the post-processors might have
        // modified the original metadata, e.g. replacing placeholders in values...
        beanFactory.clearMetadataCache();
    }

• • getBeanNamesForType()：根据传递的类型获取容器中的beanName

    // type:类的类型名称
    // includeNonSingletons:返回数据包含了非单例beanName
    // allowEagerInit: 可以提前加载初始化
    public String[] getBeanNamesForType(Class<?> type, boolean includeNonSingletons, boolean allowEagerInit) {
        if (!isConfigurationFrozen() || type == null || !allowEagerInit) {
           // 不可用缓存、类型无效、不允许提前加载初始化
           // 需要获取当前type的原始类型，继续获取数据
            return doGetBeanNamesForType(ResolvableType.forRawClass(type), includeNonSingletons, allowEagerInit);
        }
        Map<Class<?>, String[]> cache =
                (includeNonSingletons ? this.allBeanNamesByType : this.singletonBeanNamesByType);
        String[] resolvedBeanNames = cache.get(type);
        // 如果缓存已经存储了该数据，则无需再计算，直接返回即可
        if (resolvedBeanNames != null) {
            return resolvedBeanNames;
        }
        resolvedBeanNames = doGetBeanNamesForType(ResolvableType.forRawClass(type), includeNonSingletons, true);
        // 这一步就是真正的获取数据，遍历beanDefinitionNames的每一个数据，符合要求的就会加入到返回的列表中
    
        if (ClassUtils.isCacheSafe(type, getBeanClassLoader())) {
            cache.put(type, resolvedBeanNames);
            // 便于下一次获取，加入缓存中
        }
        return resolvedBeanNames;
    }

  • getBean后面还有一个参数BeanFactoryPostProcessor.class，注意看这个函数，会发现返回的是一个抽象类，结论就是nonOrderedPostProcessors添加的不是bean实例，而是beandefinition，在实例化前。

　　7.从上面代码中可以看出所有实现了BeanFactoryPostProcessor接口的bean，都被作为入参，然后调用了invokeBeanDefinitionRegistryPostProcessors或者invokeBeanFactoryPostProcessors方法去处理：对每个BeanFactoryPostProcessor接口的实现类，都调用了其接口方法，不同的是，对于实现了BeanDefinitionRegistryPostProcessor接口的bean，调用其postProcessBeanDefinitionRegistry方法的时候，入参是BeanDefinitionRegistry，而非BeanFactory，因此，实现了BeanDefinitionRegistryPostProcessor接口的bean，其postProcessBeanDefinitionRegistry在被调用时，可以通过入参BeanDefinitionRegistry来做更多和bean的定义有关的操作，例如注册bean；

    /**
     * Invoke the given BeanDefinitionRegistryPostProcessor beans.
     */
    private static void invokeBeanDefinitionRegistryPostProcessors(
            Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry) {

        for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
            postProcessor.postProcessBeanDefinitionRegistry(registry);
        }
    }

    /**
     * Invoke the given BeanFactoryPostProcessor beans.
     */
    private static void invokeBeanFactoryPostProcessors(
        Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) {

        for (BeanFactoryPostProcessor postProcessor : postProcessors) {
            postProcessor.postProcessBeanFactory(beanFactory);
        }
    } 

　　8.BeanFactoryPostProcessor 执行的整体流程：

　　　　1）ApplicationContext的refresh方法

　　　　2）ApplicationContext的invokeBeanFactoryPostProcessors方法

　　　　3）PostProcessorRegistrationDelegate的invokeBeanFactoryPostProcessors

　　9.BeanFactoryPostProcessor执行的优先级:

　　　　1）首先是实现了PriorityOrdered接口的，排序执行

　　　　2）下来是实现了Ordered接口的，排序执行

　　　　3）最后是其它（未实现排序接口），顺序执行

　　10.BeanFactoryPostProcessor获取机制：

　　　　1）首先获取手动注册ApplicationContext的集合

　　　　2）再次是通过beanFactory.getBeanNamesForType查找所有已注册的BeanFactory

PostProcessor的bean定义并实例化。

四.总结

　　1. ApplicationContext扩展类可以调用AbstractApplicationContext.addBeanFactoryPostProcessor方法，将自定义的BeanFactoryPostProcessor实现类保存到ApplicationContext中；
　　2. Spring容器初始化时，上一步中被加入到ApplicationContext的bean会被优先调用其postProcessBeanFactory方法；
　　3. 自定义的BeanFactoryPostProcessor接口实现类，也会被找出来，然后调用其postProcessBeanFactory方法；
　　4. postProcessBeanFactory方法被调用时，beanFactory会被作为参数传入，自定义类中可以使用该参数来处理bean的定义，达到业务需求；
　　5. 此时的Spring容器还没有开始实例化bean，因此自定义的BeanFactoryPostProcessor实现类不要做与bean实例有关的操作，而是做一些与bean定义有关的操作，例如修改某些字段的值，这样后面实例化的bean的就会有相应的改变；

　　6.Spring主要将BeanFactoryPostProcessor划分了两类：

• • 正常的BeanFactoryPostProcessor
  • BeanDefinitionRegistry类型的BeanDefinitionRegistryPostProcessor

　　7.在执行流程中可以看到Spring先执行了BeanDefinitionRegistryPostProcessor类型的postProcessBeanDefinitionRegistry方法，再执行BeanDefinitionRegistryPostProcessor和正常BeanFactoryPostProcessor的postProcessBeanFactory方法。

　　8.Spring对BeanDefinitionRegistryPostProcessor的解释是：允许在正常的BeanFactoryPostProcessor执行检测开始之前注册更多的自定义bean。也就是说BeanDefinitionRegistryPostProcessor的方法postProcessBeanDefinitionRegistry可以在后置处理器执行前自定义注册更多的BeanDefinition。

　　例如：Spring实现的ConfigurationClassPostProcessor用于注册注解@Configuration标识的类里面定义的BeanDefinition。