Spring拓展接口之BeanPostProcessor,我们来看看它的底层实现

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前言

  开心一刻

    小明:“妈,我被公司开除了”,妈:“啊,为哪几个呀?”, 小明:“我骂董事长是笨蛋,公司召开高层会议时需起诉我”,妈:“告你诽谤是吧?”,小明:“有的是,也许要告我泄露公司机密”

BeanPostProcessor定义

  不管三七二十一,大伙儿先来看看它的定义,看看spring是咋样描述BeanPostProcessor的

/*
 * Copyright 60

2-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.beans.factory.config;

import org.springframework.beans.BeansException;
import org.springframework.lang.Nullable;

/**
 * 允许对新的bean示例进行自定义的修改,这类检查标志接口或进行代理封装
 *
 * spring上下文会在它的beng定义中自动检测BeanPostProcessor实例,并将它们应用于后来创建的每有有五个

多

bean实例
 *
 * implement {@link #postProcessAfterInitialization}.
 * 通常,通过实现BeanPostProcessor的postProcessBeforeInitialization法律法律依据(配合标记接口,如@Autowired)来填充bean实例,
 * 通过BeanPostProcessor的postProcessAfterInitialization法律法律依据进行bean实例的代理
 *
 */
public interface BeanPostProcessor {

    /**
     * 在bean实例的初始化法律法律依据(这类InitializingBean的afterPropertiesSet或自定义的init-method)回调后来,
     * spring会应用此法律法律依据到bean实例上。一般用于bean实例的属性值的填充
     * Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean
     * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
     * or a custom init-method). The bean will already be populated with property values.
     * The returned bean instance may be a wrapper around the original.
     * <p>The default implementation returns the given {@code bean} as-is.
     * @param bean the new bean instance
     * @param beanName the name of the bean
     * @return the bean instance to use, either the original or a wrapped one;
     * if {@code null}, no subsequent BeanPostProcessors will be invoked
     * @throws org.springframework.beans.BeansException in case of errors
     * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
     */
    @Nullable
    default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

    /**
     * 在bean实例的初始化法律法律依据(这类InitializingBean的afterPropertiesSet或自定义的init-method)回调后来,
     * spring会应用此法律法律依据到bean实例上。
     * 在有FactoryBean时,此法律法律依据会在FactoryBean实例与FactoryBean的目标对象创建时各调用一次
     * Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean
     * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
     * or a custom init-method). The bean will already be populated with property values.
     * The returned bean instance may be a wrapper around the original.
     * <p>In case of a FactoryBean, this callback will be invoked for both the FactoryBean
     * instance and the objects created by the FactoryBean (as of Spring 2.0). The
     * post-processor can decide whether to apply to either the FactoryBean or created
     * objects or both through corresponding {@code bean instanceof FactoryBean} checks.
     * <p>This callback will also be invoked after a short-circuiting triggered by a
     * {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
     * in contrast to all other BeanPostProcessor callbacks.
     * <p>The default implementation returns the given {@code bean} as-is.
     * @param bean the new bean instance
     * @param beanName the name of the bean
     * @return the bean instance to use, either the original or a wrapped one;
     * if {@code null}, no subsequent BeanPostProcessors will be invoked
     * @throws org.springframework.beans.BeansException in case of errors
     * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
     * @see org.springframework.beans.factory.FactoryBean
     */
    @Nullable
    default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

}
View Code

  简单点来理解,后来spring会自动从它的所有的bean定义中检测BeanPostProcessor类型的bean定义,后来实例化它们,再将它们应用于后来创建的每有有五个 多 bean实例,在bean实例的初始化法律法律依据回调后来调用BeanPostProcessor的postProcessBeforeInitialization的法律法律依据(进行bean实例属性的填充),在bean实例的初始化法律法律依据回调后来调用BeanPostProcessor的postProcessAfterInitialization的法律法律依据(不能进行bean实例的代理封装)

应用示例

  大伙儿先来看个简单的示例,注意:将会spring后来从spring容器中的bean定义中自动检测BeanPostProcessor类型的bean定义,后来有大伙儿自定义的BeanPostProcessor要通过有這個法律法律依据注册到spring容器

  MyBeanPostProcessor

  AnimalConfig

  Dog

  完整版实例工程:spring-boot-BeanPostProcessor 大伙儿来看看启动结果

  一帮人将会会说了:“你是个逗比把,你举的這個 例子有哪几个用? 实际上,根本就不想突然总出 BeanPostProcessor的原来 用法!”  有原来 的大问题非常正常,示例中的BeanPostProcessor的有有五个 多 法律法律依据:postProcessBeforeInitialization、postProcessAfterInitialization没做任何的出理 ,都后来直接返回bean,这不后来:脱了裤子放屁?

  大伙儿细看下,会发现postProcessBeforeInitialization、postProcessAfterInitialization中各多了一行打印(),我觉得示这类果验证下Spring对BeanPostProcessor的支持、BeanPostProcessor的有有五个 多 法律法律依据的执行时机,是算不算如BeanPostProcessor 的注释所说的那样,实际应用中肯定不想这样用的。那大问题来了:BeanPostProcessor能用来干哪几个? 回答這個 大问题后来,大伙儿先来看看spring对BeanPostProcessor的底层支持

源码解析

  BeanPostProcessor的实例化与注册  

    很明显,大伙儿从spring的启动过程的refresh法律法律依据现在始于,如下图

 

    此时spring容器中所有的BeanPostProcessor都进行了实例化,并注册到了beanFactory的beanPostProcessors属性中

    registerBeanPostProcessors

public static void registerBeanPostProcessors(
        ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

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

    // Register BeanPostProcessorChecker that logs an info message when
    // a bean is created during BeanPostProcessor instantiation, i.e. when
    // a bean is not eligible for getting processed by all BeanPostProcessors.
    int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
    beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

    // Separate between BeanPostProcessors that implement PriorityOrdered,
    // Ordered, and the rest.
    // 将所有BeanPostProcessor bean定义分三类:实现了PriorityOrdered、实现了Ordered,以及剩下的常规BeanPostProcessor
    List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
    List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
    List<String> orderedPostProcessorNames = new ArrayList<>();
    List<String> nonOrderedPostProcessorNames = new ArrayList<>();
    for (String ppName : postProcessorNames) {
        if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
            // 实例化实现了PriorityOrdered接口的BeanPostProcessor
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            priorityOrderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
            orderedPostProcessorNames.add(ppName);
        }
        else {
            nonOrderedPostProcessorNames.add(ppName);
        }
    }

    // First, register the BeanPostProcessors that implement PriorityOrdered.
    // 注册实现了PriorityOrdered接口的BeanPostProcessor到beanFactory的beanPostProcessors属性中
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

    // Next, register the BeanPostProcessors that implement Ordered.
    List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
    for (String ppName : orderedPostProcessorNames) {
        // 实例化实现了Ordered接口的BeanPostProcessor
        BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
        orderedPostProcessors.add(pp);
        if (pp instanceof MergedBeanDefinitionPostProcessor) {
            internalPostProcessors.add(pp);
        }
    }
    // 注册实现了Ordered接口的BeanPostProcessor到beanFactory的beanPostProcessors属性中
    sortPostProcessors(orderedPostProcessors, beanFactory);
    registerBeanPostProcessors(beanFactory, orderedPostProcessors);

    // Now, register all regular BeanPostProcessors.
    List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
    for (String ppName : nonOrderedPostProcessorNames) {
        // 实例化剩下的所有的常规的BeanPostProcessors
        BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
        nonOrderedPostProcessors.add(pp);
        if (pp instanceof MergedBeanDefinitionPostProcessor) {
            internalPostProcessors.add(pp);
        }
    }
    registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

    // Finally, re-register all internal BeanPostProcessors.
    // 注册所有常规的的BeanPostProcessor到beanFactory的beanPostProcessors属性中
    sortPostProcessors(internalPostProcessors, beanFactory);
    registerBeanPostProcessors(beanFactory, internalPostProcessors);

    // Re-register post-processor for detecting inner beans as ApplicationListeners,
    // moving it to the end of the processor chain (for picking up proxies etc).
    beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}
View Code

  BeanPostProcessor的生效时机

    前面大伙儿将会知道,spring会应用BeanPostProcessor于后来创建的每有有五个 多 bean实例,具体spring是咋样做到的了,大伙儿仔细来看看

    finishBeanFactoryInitialization法律法律依据实例化所有剩余的、非延迟初始化的单例(默认清况 下spring的bean有的是非延迟初始化单例),具体如下

BeanPostProcessor应用场景

  我觉得有后来大伙儿弄清楚了BeanPostProcessor的执行时机:在bean实例化后来、初始化前后被执行,允许大伙儿对bean实例进行自定义的修改;有后来大伙儿明白了這個 时机点,大伙儿就能分辨出BeanPostProcessor适用于哪几个需求场景,哪几个需求场景不能用BeanPostProcessor来实现

  spring中含后来有BeanPostProcessor的实现,大伙儿接触的比较多的自动装配:AutowiredAnnotationBeanPostProcessor也是BeanPostProcessor的实现之一,关于自动装配我会在下篇博文中与大伙儿一起探索

总结

  spring中bean的生命周期如下图

    引用自:Spring实战系列(三)-BeanPostProcessor的妙用