AbstractBeanFactory获取bean周期

AbstractBeanFactory是IOC容器实现的骨架，当从Spring容器获取Bean时，调用的正是getBean方法。实现步骤如下
  检查单例缓存
  在父工厂中查找
  初始化当前bean依赖的beans(depends-on)
  根据scope使用不同的创建方式bean
  检查获取的bean是FactoryBean类型还是普通bean
  可能的类型转换

  单例缓存
  spring中单例理解不同与设计模式中的单例，前者指一个容器对应类只有一个实例，后者指一个classloader有一个实例。Spring bean工厂将scope="singleton"的实例缓存到map中，下次查询时可从缓存缓存中取。对于这种scope的创建大致可用下图描述

  父工厂
   spring bean工厂可有父子关系，当前工厂中找不到时可从父工厂中查找，这也说明了每个工厂都有它对应的单例缓存。而非设计模式JVM中的单例理解

   depends-on
   指定了bean之间的依赖关系，同时也指定了bean初始化的先后顺序，或如果是单例也指定销毁时的先后顺序：
   初始化：依赖的类都要先于指定类
   销毁：依赖的类要晚于指定类
   
   scope
  singleton  指定类对每个bean Factory只有一个实例，生命周期完全有由spring容器管理，包括初始化时的回调和销毁时的回调
  prototype 每次请求都会创建一个新的实例,spring不会记录实例状态，也不负责销毁，即支持初始化回调，不支持销毁时的回调。客户端必须负责清理资源，可以使用初始化时的bean post-processor保存引用以便后续销毁。
  custom scope bean工厂支持注册自定义scope,可在初始化时由beanFactoryPostProcessor回调完成。AbstractApplicationContext提供了模版在所有beanFactoryPostprocessor之前修改bean定义，在其子类AbstractRefreshableWebApplicationContext的该方法实现如下，可以看到requestScope,sessionScope的实现
	/**
	 * Register ServletContextAwareProcessor.
	 * @see ServletContextAwareProcessor
	 */
	protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
		beanFactory.registerScope(SCOPE_REQUEST, new RequestScope());
		beanFactory.registerScope(SCOPE_SESSION, new SessionScope(false));
		beanFactory.registerScope(SCOPE_GLOBAL_SESSION, new SessionScope(true));

		beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext, this.servletConfig));
		beanFactory.ignoreDependencyInterface(ServletContextAware.class);
		beanFactory.ignoreDependencyInterface(ServletConfigAware.class);
	}

 我们自定义实现可以使用org.springframework.beans.factory.config.CustomScopeConfigurer负责注册。自定义Scope许扩展 org.springframework.beans.factory.config.Scope接口，如SimpleMapScope。
/*
 * Copyright 2002-2008 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 java.io.Serializable;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

import org.springframework.beans.factory.ObjectFactory;

/**
 * @author Juergen Hoeller
 */
public class SimpleMapScope implements Scope, Serializable {

	private final Map map = new HashMap();

	private final List callbacks = new LinkedList();


	public SimpleMapScope() {
	}

	public final Map getMap() {
		return this.map;
	}


	public Object get(String name, ObjectFactory objectFactory) {
		synchronized (this.map) {
			Object scopedObject = this.map.get(name);
			if (scopedObject == null) {
				scopedObject = objectFactory.getObject();
				this.map.put(name, scopedObject);
			}
			return scopedObject;
		}
	}

	public Object remove(String name) {
		synchronized (this.map) {
			return this.map.remove(name);
		}
	}

	public void registerDestructionCallback(String name, Runnable callback) {
		this.callbacks.add(callback);
	}

	public Object resolveContextualObject(String key) {
		return null;
	}

	public void close() {
		for (Iterator it = this.callbacks.iterator(); it.hasNext();) {
			Runnable runnable = (Runnable) it.next();
			runnable.run();
		}
	}

	public String getConversationId() {
		return null;
	}

}
   创建方式比较
   Spring实现中，不管是哪种创建实现方式都差不多，比如设置正在创建标志避免循环引用导致的内存溢出、最终通过Spring配置蓝图创建。单例的创建多了一些缓存的设置，prototype更简单直接调用createbean根据Spring配置蓝图创建；自定义scope调用get方法，最终还是使用Spring ObjectFactory创建蓝图。
   
   检查bean FactoryBean
   当bean得到之后，必须进行合理的检查才能使用。
   如果bean是FactoryBean实例，检索的bean id 是以"&"开头直接返回
   如果bean是FactoryBean实例，检索的bean id不是"&"开头，调用Factorybean的getObject方法
   如果bean不是FactoryBean实例，检索的bean id 是以"&"开头，报错
   如果bean不是FactoryBean实例，检索的bean idb不是以"&"开头，返回
 
   短路shut-cut
   Spring容器给了InstantiationAwareBeanPostProcessor机会在Bean根据Spring配置创建之前执行回调，如果返回不会空则getBean终止：
   postProcessBeforeInstantiation 回调实例化之前调用，返回值不为空则执行
   BeanPostProcessor的applyBeanPostProcessorsAfterInitialization方法
   
   创建实例
   1.使用适当的实例化策略：工厂方法，构造器装配，反射newInstance创建内存对象
   2.可能的MergedBeanDefinitionPostProcessor注解处理
   3.可能的singletonFactory创建
   4.装配bean
  5.调用初始化方法及beanPostProcessor方法
   6.如果在beanPostProcessor实现中改变了传入bean的地址，比如自动代理将会创建一个新的地址返回，则会报错org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'bean1': Bean with name 'bean1' has been injected into other beans [bean2] in its raw version as part of a circular reference, but has eventually been wrapped (for example as part of auto-proxy creation). This means that said other beans do not use the final version of the bean. This is often the result of over-eager type matching - consider using 'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.

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