Spring系列之核心容器

【回顾】

在上篇博客中，我们清楚了Spring的核心IOC，博客的结尾，提出了关于容器的问题。在Spring框架中，容器扮演者重要的角色。容器是什么？Java容器？Spring容器？这几个词，大家都很熟悉，但真正知道么？本篇博客的重点分析Spring中的核心容器。容器和Java容器不做详细介绍。

【容器】

容器，从字面角度很容易理解，就是用来贮藏东西的。从计算机的角度，可粗略地分为Web容器和编程容器。

Web容器是应用服务器中位于组件和平台之间的接口集合。如WebLogic、Tomcat等。

编程容器容器是用来存储和组织其他对象的对象。如Java内部容器类（Map、List等）。

容器可以管理对象的生命周期、对象与对象之间的依赖关系，您可以使用一个配置文件（通常是XML），在上面定义好对象的名称、如何产生（Prototype 方式或Singleton
方式）、哪个对象产生之后必须设定成为某个对象的属性等，在启动容器之后，所有的对象都可以直接取用，不用编写任何一行程序代码来产生对象，或是建立对象与对象之间的依赖关系。这也正是使用Spring框架给我们带来的好处。

【Spring核心容器】

Spring框架中，谁扮演着容器角色？下面是Spring的主要接口设计关系图：

从图中，我们可以做出以下分析：

	1.从接口BeanFactory到HierarchicalBeanFactory，再到ConfigurableBeanFactory,这是一条主要的BeanFactory设计路径。
	在这条接口设计路径中，BeanFactory，是一条主要的BeanFactory设计路径，其定义了基本的Ioc容器的规范。在这个接口定义中，包括了getBean()这样的Ioc容器的基本方法（通过这个方法可以从容器中取得Bean）。
	而HierarchicalBeanFactory接口在继承了BeanFactory的基本接口后，增加了getParentBeanFac
tory()的接口功能，使BeanFactory具备了双亲Ioc容器的管理功能。
	在接下来的ConfigurableBeanFactory接口中，主要定义了一些对BeanFactory的配置功能，比如通过setParentBeanFactory()设置双亲Ioc容器，通过addBeanPostProcessor()配置Bean后置处理器，等等。
	通过这些接口设计的叠加，定义了BeanFactory就是最简单的Ioc容器的基本功能。
 	2.第二条接口设计主线是，以ApplicationContext作为核心的接口设计，这里涉及的主要接口设计有，从BeanFactory到ListableBeanFactory，再到ApplicationContext，再到我们常用的WebApplicationContext或者ConfigurableApplicationContext接口。
	我们常用的应用基本都是org.framework.context 包里的WebApplicationContext或者ConfigurableApplicationContext实现。
	在这个接口体现中，ListableBeanFactory和HierarchicalBeanFactory两个接口，连接BeanFactory接口定义和ApplicationContext应用的接口定义。
	在ListableBeanFactory接口中，细化了许多BeanFactory的接口功能，比如定义了getBeanDefinitionNames()接口方法；
	对于ApplicationContext接口，它通过继承MessageSource、ResourceLoader、ApplicationEventPublisher接口，在BeanFactory简单Ioc容器的基础上添加了许多对高级容器的特性支持。
	3.这个接口系统是以BeanFactory和ApplicationContext为核心设计的，而BeanFactory是Ioc容器中最基本的接口。
	在ApplicationContext的设计中，一方面，可以看到它继承了BeanFactory接口体系中的ListableBeanFactory、AutowireCapableBeanFactory、HierarchicalBeanFactory等BeanFactory的接口，具备了BeanFactory Ioc容器的基本功能；
	另一方面，通过继承MessageSource、ResourceLoadr、ApplicationEventPublisher这些接口，BeanFactory为ApplicationContext赋予了更高级的Ioc容器特性。对于ApplicationContext而言，为了在Web环境中使用它，还设计了WebApplicationContext接口，而这个接口通过继承ThemeSource接口来扩充功能。

BeanFactory源码：

/*
 * Copyright 2002-2006 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;

import org.springframework.beans.BeansException;

/**
 * The root interface for accessing a Spring bean container.
 * This is the basic client view of a bean container; further interfaces
 * such as <code>ListableBeanFactory</code> and <code>ConfigurableBeanFactory</code>
 * are available for specific purposes.
 *
 * <p>This interface is implemented by objects that hold a number of bean definitions,
 * each uniquely identified by a String name. Depending on the bean definition,
 * the factory will return either an independent instance of a contained object
 * (the Prototype design pattern), or a single shared instance (a superior
 * alternative to the Singleton design pattern, in which the instance is a
 * singleton in the scope of the factory). Which type of instance will be returned
 * depends on the bean factory configuration: the API is the same. The Singleton
 * approach is more useful and more common in practice.
 *
 * <p>The point of this approach is that the BeanFactory is a central registry
 * of application components, and centralizes configuration of application
 * components (no more do individual objects need to read properties files,
 * for example). See chapters 4 and 11 of "Expert One-on-One J2EE Design and
 * Development" for a discussion of the benefits of this approach.
 *
 * <p>Note that it is generally better to rely on Dependency Injection
 * ("push" configuration) to configure application objects through setters
 * or constructors, rather than use any form of "pull" configuration like a
 * BeanFactory lookup. Spring's Dependency Injection functionality is
 * implemented using BeanFactory and its subinterfaces.
 *
 * <p>Normally a BeanFactory will load bean definitions stored in a configuration
 * source (such as an XML document), and use the org.springframework.beans package
 * to configure the beans. However, an implementation could simply return Java
 * objects it creates as necessary directly in Java code. There are no constraints
 * on how the definitions could be stored: LDAP, RDBMS, XML, properties file etc.
 * Implementations are encouraged to support references amongst beans, to either
 * Singletons or Prototypes.
 *
 * <p>In contrast to the methods in ListableBeanFactory, all of the methods in this
 * interface will also check parent factories if this is a HierarchicalBeanFactory.
 * If a bean is not found in this factory instance, the immediate parent is asked.
 * Beans in this factory instance are supposed to override beans of the same name
 * in any parent factory.
 *
 * <p>Bean factory implementations should support the standard bean lifecycle interfaces
 * as far as possible. The full set of initialization methods and their standard order is:<br>
 * 1. BeanNameAware's <code>setBeanName</code><br>
 * 2. BeanClassLoaderAware's <code>setBeanClassLoader</code><br>
 * 3. BeanFactoryAware's <code>setBeanFactory</code><br>
 * 4. ResourceLoaderAware's <code>setResourceLoader</code>
 * (only applicable when running in an application context)<br>
 * 5. ApplicationEventPublisherAware's <code>setApplicationEventPublisher</code>
 * (only applicable when running in an application context)<br>
 * 6. MessageSourceAware's <code>setMessageSource</code>
 * (only applicable when running in an application context)<br>
 * 7. ApplicationContextAware's <code>setApplicationContext</code>
 * (only applicable when running in an application context)<br>
 * 8. ServletContextAware's <code>setServletContext</code>
 * (only applicable when running in a web application context)<br>
 * 9. <code>postProcessBeforeInitialization</code> methods of BeanPostProcessors<br>
 * 10. InitializingBean's <code>afterPropertiesSet</code><br>
 * 11. a custom init-method definition<br>
 * 12. <code>postProcessAfterInitialization</code> methods of BeanPostProcessors
 *
 * <p>On shutdown of a bean factory, the following lifecycle methods apply:<br>
 * 1. DisposableBean's <code>destroy</code><br>
 * 2. a custom destroy-method definition
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @since 13 April 2001
 * @see ListableBeanFactory
 * @see org.springframework.beans.factory.config.ConfigurableBeanFactory
 * @see BeanNameAware#setBeanName
 * @see BeanClassLoaderAware#setBeanClassLoader
 * @see BeanFactoryAware#setBeanFactory
 * @see org.springframework.context.ResourceLoaderAware#setResourceLoader
 * @see org.springframework.context.ApplicationEventPublisherAware#setApplicationEventPublisher
 * @see org.springframework.context.MessageSourceAware#setMessageSource
 * @see org.springframework.context.ApplicationContextAware#setApplicationContext
 * @see org.springframework.web.context.ServletContextAware#setServletContext
 * @see org.springframework.beans.factory.config.BeanPostProcessor#postProcessBeforeInitialization
 * @see InitializingBean#afterPropertiesSet
 * @see org.springframework.beans.factory.support.RootBeanDefinition#getInitMethodName
 * @see org.springframework.beans.factory.config.BeanPostProcessor#postProcessAfterInitialization
 * @see DisposableBean#destroy
 * @see org.springframework.beans.factory.support.RootBeanDefinition#getDestroyMethodName
 */
public interface BeanFactory {

	/**
	 * Used to dereference a FactoryBean and distinguish it from beans
	 * <i>created</i> by the FactoryBean. For example, if the bean named
	 * <code>myEjb</code> is a FactoryBean, getting <code>&myEjb</code> will
	 * return the factory, not the instance returned by the factory.
	 */
	String FACTORY_BEAN_PREFIX = "&";

	/**
	 * Return an instance, which may be shared or independent, of the given bean name.
	 * This method allows a Spring BeanFactory to be used as a replacement for the
	 * Singleton or Prototype design pattern.
	 * <p>Callers may retain references to returned objects in the case of Singleton beans.
	 * <p>Translates aliases back to the corresponding canonical bean name.
	 * Will ask the parent factory if the bean cannot be found in this factory instance.
	 * @param name the name of the bean to return
	 * @return the instance of the bean
	 * @throws NoSuchBeanDefinitionException if there is no bean definition
	 * with the specified name
	 * @throws BeansException if the bean could not be obtained
	 */
	Object getBean(String name) throws BeansException;

	/**
	 * Return an instance (possibly shared or independent) of the given bean name.
	 * <p>Behaves the same as getBean(String), but provides a measure of type safety by
	 * throwing a Spring BeansException if the bean is not of the required type.
	 * This means that ClassCastException can't be thrown on casting the result correctly,
	 * as can happen with <code>getBean(String)</code>.
	 * @param name the name of the bean to return
	 * @param requiredType type the bean must match. Can be an interface or superclass
	 * of the actual class, or <code>null</code> for any match. For example, if the value
	 * is <code>Object.class</code>, this method will succeed whatever the class of the
	 * returned instance.
	 * @return an instance of the bean (never <code>null</code>)
	 * @throws BeanNotOfRequiredTypeException if the bean is not of the required type
	 * @throws NoSuchBeanDefinitionException if there's no such bean definition
	 * @throws BeansException if the bean could not be created
	 */
	Object getBean(String name, Class requiredType) throws BeansException;

	/**
	 * Does this bean factory contain a bean definition with the given name?
	 * <p>Will ask the parent factory if the bean cannot be found in this factory instance.
	 * @param name the name of the bean to query
	 * @return whether a bean with the given name is defined
	 */
	boolean containsBean(String name);

	/**
	 * Is this bean a singleton? That is, will <code>getBean</code> always return the same object?
	 * <p>Will ask the parent factory if the bean cannot be found in this factory instance.
	 * @param name the name of the bean to query
	 * @return is this bean a singleton
	 * @throws NoSuchBeanDefinitionException if there is no bean with the given name
	 * @see #getBean
	 */
	boolean isSingleton(String name) throws NoSuchBeanDefinitionException;

	/**
	 * Determine the type of the bean with the given name.
	 * More specifically, checks the type of object that <code>getBean</code> would return.
	 * For a FactoryBean, returns the type of object that the FactoryBean creates.
	 * @param name the name of the bean to query
	 * @return the type of the bean, or <code>null</code> if not determinable
	 * @throws NoSuchBeanDefinitionException if there is no bean with the given name
	 * @since 1.1.2
	 * @see #getBean
	 * @see FactoryBean#getObjectType()
	 */
	Class getType(String name) throws NoSuchBeanDefinitionException;

	/**
	 * Return the aliases for the given bean name, if defined.
	 * <p>If the given name is an alias, the corresponding original bean name
	 * and other aliases (if any) will be returned, with the original bean name
	 * being the first element in the array.
	 * <p>Will ask the parent factory if the bean cannot be found in this factory instance.
	 * @param name the bean name to check for aliases
	 * @return the aliases, or an empty array if none
	 */
	String[] getAliases(String name);

}

ApplicationContext源码：

/*
 * Copyright 2002-2006 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.context;

import org.springframework.beans.factory.HierarchicalBeanFactory;
import org.springframework.beans.factory.ListableBeanFactory;
import org.springframework.beans.factory.config.AutowireCapableBeanFactory;
import org.springframework.core.io.support.ResourcePatternResolver;

/**
 * Central interface to provide configuration for an application.
 * This is read-only while the application is running, but may be
 * reloaded if the implementation supports this.
 *
 * <p>An ApplicationContext provides:
 * <ul>
 * <li>Bean factory methods, inherited from ListableBeanFactory.
 * This avoids the need for applications to use singletons.
 * <li>The ability to resolve messages, supporting internationalization.
 * Inherited from the MessageSource interface.
 * <li>The ability to load file resources in a generic fashion.
 * Inherited from the ResourceLoader interface.
 * <li>The ability to publish events. Implementations must provide a means
 * of registering event listeners.
 * <li>Inheritance from a parent context. Definitions in a descendant context
 * will always take priority. This means, for example, that a single parent
 * context can be used by an entire web application, while each servlet has
 * its own child context that is independent of that of any other servlet.
 * </ul>
 *
 * <p>In addition to standard bean factory lifecycle capabilities,
 * ApplicationContext implementations need to detect ApplicationContextAware
 * beans and invoke the setApplicationContext method accordingly.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see ApplicationContextAware#setApplicationContext
 * @see ConfigurableApplicationContext
 */
public interface ApplicationContext extends ListableBeanFactory, HierarchicalBeanFactory,
		MessageSource, ApplicationEventPublisher, ResourcePatternResolver {

	/**
	 * Return the parent context, or <code>null</code> if there is no parent,
	 * and this is the root of the context hierarchy.
	 * @return the parent context, or <code>null</code> if there is no parent
	 */
	ApplicationContext getParent();

	/**
	 * Expose AutowireCapableBeanFactory functionality for this context.
	 * <p>This is not typically used by application code, except for the purpose
	 * of initializing bean instances that live outside the application context,
	 * applying the Spring bean lifecycle (fully or partly) to them.
	 * <p>Alternatively, the internal BeanFactory exposed by the
	 * ConfigurableApplicationContext interface offers access to the
	 * AutowireCapableBeanFactory interface too. The present method mainly
	 * serves as convenient, specific facility on the ApplicationContext
	 * interface itself.
	 * @throws IllegalStateException if the context does not support
	 * the AutowireCapableBeanFactory interface or does not hold an autowire-capable
	 * bean factory yet (usually if <code>refresh()</code> has never been called)
	 * @see ConfigurableApplicationContext#refresh()
	 * @see ConfigurableApplicationContext#getBeanFactory()
	 */
	AutowireCapableBeanFactory getAutowireCapableBeanFactory() throws IllegalStateException;

	/**
	 * Return a friendly name for this context.
	 * @return a display name for this context
	*/
	String getDisplayName();

	/**
	 * Return the timestamp when this context was first loaded.
	 * @return the timestamp (ms) when this context was first loaded
	 */
	long getStartupDate();

}

【知识总结】

        BeanFacotry是spring中比较原始的Factory。它无法支持spring的许多插件，如AOP功能、Web应用等。
        ApplicationContext接口,它由BeanFactory接口派生而来，因而提供BeanFactory所有的功能。ApplicationContext以一种更向面向框架的方式工作以及对上下文进行分层和实现继承，ApplicationContext包还提供了以下的功能：
      ? MessageSource, 提供国际化的消息访问 
      ? 资源访问，如URL和文件 
      ? 事件传播 
      ? 载入多个（有继承关系）上下文 ，使得每一个上下文都专注于一个特定的层次，比如应用的web层  
        BeanFactroy采用的是延迟加载形式来注入Bean的，即只有在使用到某个Bean时(调用getBean())，才对该Bean进行加载实例化，这样，我们就不能发现一些存在的Spring的配置问题。而ApplicationContext则相反，它是在容器启动时，一次性创建了所有的Bean。这样，在容器启动时，我们就可以发现Spring中存在的配置错误。

【学习心得】
	1.在学习框架的时候，从源码着手，会是个比较清晰的方向，毕竟是第一手资料。再结合一些视频、书籍和文章的资料，看源码的困难也减少了。
	2.再看源码的时候，注释是非常重要的。代码很简单，可能觉得没什么问题，而当你看完注释后，你会对源码产生更加深刻的理解。

	参考资料：Spring源码分析