Spring Bean的載入，SpringBean載入

Spring Bean的載入，SpringBean載入
Spring載入bean的原則：不等bean建立完成就會將建立bean的ObjectFactory提早曝光加入到緩衝中。 單例bean在Spring容器裡只會建立一次，後續建立時會首先從緩衝中擷取，嘗試載入，不成功則從singletonFatories中載入。當存在循環相依性的時候，依據Spring的載入bean原則，下一個bean需要依賴上一個bean的時候直接使用ObjectFactory。 緩衝中儲存的是bean的原始狀態，需要進行bean的執行個體化操作。 Spring初始化bean的時候，會首先初始化這個bean所對應的依賴。

package org.springframework.beans.factory;/*** Interface to be implemented by objects used within a {@link BeanFactory}* which are themselves factories. If a bean implements this interface,* it is used as a factory for an object to expose, not directly as a bean* instance that will be exposed itself.*/public interface FactoryBean<T> {  /**    * Return an instance (possibly shared or independent) of the object    * managed by this factory.    */  T getObject() throws Exception;  /**    * Return the type of object that this FactoryBean creates,    * or {@code null} if not known in advance.      */  Class<?> getObjectType();  /**    * Is the object managed by this factory a singleton? That is,    * will {@link #getObject()} always return the same object    * (a reference that can be cached)?    * 單例對象會放在Spring單例緩衝池中    */  boolean isSingleton();}

Factory 方法配置bean如下：

<bean id="book" class="com.xxx.model.BookFactory"/>

BookFactory實現了FactoryBean，則當使用getBean("book")時，返回FactoryBean#getObject()方法返回的對象，即FactoryBean#getObject()代理了getBean()方法：

Book book = ctx.getBean("book");

如果要擷取BookFactoryBean對象，則需要使用首碼“&”，使用如下：

BookFactory bookFactory = ctx.getBean("&book");

單例Bean（singleton）擷取步驟：   singletonObjects<BeanName, BeanInstance>.get(beanName)：Map單例緩衝擷取。synchronized(this.singletonObjects)，全域變數同步。        ↓↓        ↓↓==Null        ↓↓ earlySingletonObjects<BeanName, BeanInstance> .get(beanName)：處理循環參考依賴檢測。        ↓↓        ↓↓==Null        ↓↓ singletonFactories<BeanName, BeanFactory> .get(beanName)：調用 相應單例建立工廠getObject()返回Bean對象。        ↓↓        -->earlySingletonObjects.put(beanName, singletonObject)儲存擷取的Bean執行個體。        --> singletonFactories.remove(beanName)移除beanName對應單例工廠。  Bean建立：  Bean初始化：Aware方法，Post處理，Init處理。