spring-core-3-26 | Spring IoC容器：BeanFactory和ApplicationContext谁才是Spring IoC容器？

本文主要是介绍spring-core-3-26 | Spring IoC容器：BeanFactory和ApplicationContext谁才是Spring IoC容器？，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

Spring IoC 容器

BeanFactory 和ApplicationContext 谁才是Spring IoC 容器？

真正的IOC的底层实现就是BeanFactory的实现类，但ApplicationContext 在底层组合了一个 BeanFactory 实现,是委托DefaultListableBeanFactory来操作getBean等方法的。

也因此
System.out.println(userRepository.getBeanFactory() ==
applicationContext); 是false尽管他们都复用了同样的接口 BeanFactory, 但他们不是一个对象

代码示例

/** Licensed to the Apache Software Foundation (ASF) under one or more* contributor license agreements.  See the NOTICE file distributed with* this work for additional information regarding copyright ownership.* The ASF licenses this file to You 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.geekbang.thinking.in.spring.ioc.overview.dependency.injection;import org.geekbang.thinking.in.spring.ioc.overview.repository.UserRepository;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;/**** 26 | Spring IoC容器：BeanFactory和ApplicationContext谁才是Spring IoC容器？* 见下面的 whoIsIoCContainer()** @author <a href="mailto:mercyblitz@gmail.com">Mercy</a>* @since*/
public class DependencyInjectionDemo {/*** 26 | Spring IoC容器：BeanFactory和ApplicationContext谁才是Spring IoC容器？** @param userRepository* @param applicationContext*/private static void whoIsIoCContainer(UserRepository userRepository,//BeanFactory beanFactoryApplicationContext applicationContext) {/*ApplicationContext其实就是BeanFactory, 为什么这么说?首先要参看spring官方文档对于beanFactory和applicationContext的解释:https://docs.spring.io/spring-framework/docs/5.2.2.RELEASE/spring-framework-reference/core.html1.1节中The org.springframework.beans and org.springframework.context packages are the basisfor Spring Framework’s IoC container.org.springframework.beans 和 org.springframework.context是 spring Ioc容器的相关包The BeanFactory interface provides an advanced configuration mechanism capable ofmanaging any type of object.BeanFactory接口提供了一些高级配置的一个机制, 能够来管理任何类型的对象.(这里用object, 而不是bean, 是非常准确的, 因为我们前面知道, IoC的依赖来源有bean也有依赖(非bean))ApplicationContext is a sub-interface of BeanFactory. It adds:ApplicationContext 是 BeanFactory的子接口, 同时还提供了下面的特性:Easier integration with Spring’s AOP features简化了和spring AOP特性的整合Message resource handling (for use in internationalization)消息资源的处理(用于国际化)Event publication事件的发布, 就是spring的事件Application-layer specific contexts such as the WebApplicationContext foruse in web applications.用于应用级别的上下文, 比如WebApplicationContext 使用在web场景的应用下In short, the BeanFactory provides the configuration framework and basic functionality,总而言之, BeanFactory提供了一个配置的框架且是基本的功能and the ApplicationContext adds more enterprise-specific functionality.并且 ApplicationContext 增加了一些企业级应用的特性.到这里我们可以认为BeanFactory就是一个基本的IoC容器, 而ApplicationContext是它的一个超集The ApplicationContext is a complete superset of the BeanFactory and is used exclusivelyin this chapter in descriptions of Spring’s IoC container.For more information on using the BeanFactory instead of the ApplicationContext, see [beans-beanfactory].*/// 这个表达式为什么不会成立System.out.println(userRepository.getBeanFactory() == applicationContext);/*ApplicationContext is BeanFactory, 如官方文档所说, ApplicationContext就是BeanFactory的一个超集我们从子类往上找, 按照这样的方向去找找名堂:ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:/META-INF/dependency-injection-context.xml");ClassPathXmlApplicationContext => AbstractXmlApplicationContext => AbstractRefreshableConfigApplicationContext=> AbstractRefreshableApplicationContext => AbstractApplicationContext在最后的抽象类 AbstractApplicationContext 中是这样的public abstract class AbstractApplicationContext extends DefaultResourceLoaderimplements ConfigurableApplicationContext {ConfigurableApplicationContext 是配置模式, 这是一种可写的模式在这个类中寻找方法 getBeanFactory()@Overridepublic abstract ConfigurableListableBeanFactory getBeanFactory() throws IllegalStateException;可见也是覆盖了接口的方法, 那么这个接口就是 ConfigurableApplicationContext那么这里就有些奇怪, 看类头是这样的:public interface ConfigurableApplicationContext extends ApplicationContext, Lifecycle, Closeable {ApplicationContext不就是BeanFactory的子接口么ConfigurableApplicationContext <- ApplicationContext <- BeanFactory这里有两个问题:为什么ConfigurableApplicationContext要特意提供一个方法getBeanFactory()? 直接获取不到父类对象么?为什么System.out.println(userRepository.getBeanFactory() == applicationContext); 是false呢?那么ConfigurableApplicationContext既然是可写模式, 就回提供set方法:可以找到void setParent(@Nullable ApplicationContext parent);但是没有 setBeanFactory??往回找到 ConfigurableApplicationContext 的实现类  AbstractApplicationContext 的 getBeanFactory()这里就给按层往子类找, 有可能是在中间的抽象类实现的,用 ctrl + F12 搜索方法, 会发现实现是放在中间的抽象类 AbstractRefreshableApplicationContext@Overridepublic final ConfigurableListableBeanFactory getBeanFactory() {synchronized (this.beanFactoryMonitor) {if (this.beanFactory == null) {throw new IllegalStateException("BeanFactory not initialized or already closed - " +"call 'refresh' before accessing beans via the ApplicationContext");}return this.beanFactory;}}看一下类中beanFactory变量:@Nullableprivate DefaultListableBeanFactory beanFactory;会发现这个 beanFactory 是一个组合的, 就是说这里代码是将 beanFactory 的实现 DefaultListableBeanFactory来组合进来了, 并不是去完全抽象或继承的这个类.那么这也就解释了上面的两个问题userRepository.getBeanFactory()获取的也正是 DefaultListableBeanFactory这里先提供一个先入为主的概念:在上下文里面的实现是采用了一种组合的方式, 同时在接口上面又是 extends 关系这种方式有点像代理再去看getBean()的实现:在 AbstractApplicationContext 中:@Overridepublic <T> T getBean(Class<T> requiredType) throws BeansException {assertBeanFactoryActive();return getBeanFactory().getBean(requiredType);}这里就是先getBeanFactory(), 相当于我们先用代理对象去查找BeanFactory的实现, 并不是自己要具备这样的能力,而是外面组装了一个组合对象来帮助我们做这个事情结论是真正的IOC的底层实现就是BeanFactory的实现类，但 ApplicationContext 在底层组合了一个 BeanFactory 实现,是委托DefaultListableBeanFactory来操作getBean等方法的。也因此 System.out.println(userRepository.getBeanFactory() == applicationContext); 是false尽管他们都复用了同样的接口 BeanFactory, 但他们不是一个对象*/}}