Spring源码解析——start from BeanFactory（一）
先来看一下我们学习Spring时候的ABC代码：
BeanFactory beanFactory=new ClassPathXmlApplicationContext("applicationContext.xml");
UserManager userManager=(UserManager)beanFactory.getBean("UserManagerImpl");
userManager.add("dd","d");通过加在含有bean配置关系的映射文件，get到我们的beanFactory容器，之后就可以从容器中get bean了。接着，我们将跟着这几行最简单代码，来深入search下spring是如何实现IOC 容器的。
一，Spring容器的核心规范
先上源码：
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);
}
上面一段是从spring源码里面拽出来的，在BeanFactory里面，定义了Spring容器最基本的规范，下面我们来依次讲解下各个方法：
1，String FACTORY_BEAN_PREFIX = "&";
对FactoryBean的转义定义，因为如果使用bean的名字检索FactoryBean得到的对象是工厂生成的对象，如果需要得到工厂本身，需要转义；例如：myEjb是一个FactoryBean,&myEjb将会得到一个工厂，而不是工厂返回的实例。
关于BeanFacoty与FactoryBean: BeanFactory是个Factory，也就是IOC容器或对象工厂，FactoryBean是个Bean。在Spring中，所有的Bean都是由BeanFactory(也就是IOC容器)来进行管理的。但对FactoryBean而言，这个Bean不是简单的Bean，而是一个能生产或者修饰对象生成的工厂Bean,它的实现与设计模式中的工厂模式和修饰器模式类似。(from :http://chenzehe.iteye.com/blog/1481476)
可以看出FactoryBean主要是为了简化复杂bean的装配而产生的。
2,Object getBean(String name) throws BeansException;
根据bean的名字，获取在IOC容器中得到bean实例
3，Object getBean(String name, Class requiredType) throws BeansException;
根据了bean的名字和类型来获取bean实例，比上个方法多了类型条件验证，增强了类型安全验证机制。
4，boolean containsBean(String name);
根据名称查找是否容器中含有这个bean
5,boolean isSingleton(String name) throws NoSuchBeanDefinitionException;
判断bean是否为单例的。
6，Class getType(String name) throws NoSuchBeanDefinitionException;
得到bean类型的类类型，可能会抛出类不存在的异常。
7，String[] getAliases(String name);
得到bean的别名，如果根据别名检索，那么其原名也会被检索出来。
二，从ClassPathXmlApplicationContext到BeanFactory
BeanFactory只是定义了容器的规范，spring为容器的实现提供了很多实现类，先来看看我们代码里面，从ClassPathXmlApplicationContext到BeanFactory经历了多少级：
ClassPathXmlApplication虽然提供了好几个构造函数，但是，最终还是会调用：
public ClassPathXmlApplicationContext(String[] paths, Class clazz, ApplicationContext parent)
throws BeansException {
super(parent);
Assert.notNull(paths, "Path array must not be null");
Assert.notNull(clazz, "Class argument must not be null");
this.configResources = new Resource[paths.length];
for (int i = 0; i < paths.length; i++) {
this.configResources[i] = new ClassPathResource(paths[i], clazz);
}
refresh();
}构造函数里面，主要就是调用父类的构造函数，然后我们沿着继承链找：
之后的代码估计是加在配置资源，接着是refresh方法，这个方法的真正实现在AbstractApplicationContext这个抽象类中：
/*创建 BeanFactory 工厂的过程
refresh是一个刷新配置的过程，如果Context有可更新的子类，
当BeanFactory已存在就可更新，如果没有就新创建
*/
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
this.startupTime = System.currentTimeMillis();
synchronized (this.activeMonitor) {
this.active = true;
}
//准备刷新上下文环境
refreshBeanFactory();
//初始化beanFactory,并进行配置文件的读取
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
// Tell the internal bean factory to use the context's class loader.
beanFactory.setBeanClassLoader(getClassLoader());
// Populate the bean factory with context-specific resource editors.
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this));
// Configure the bean factory with context semantics.
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
// 子类覆盖方法做额外处理
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered with the context instance.
for (Iterator it = getBeanFactoryPostProcessors().iterator(); it.hasNext();) {
BeanFactoryPostProcessor factoryProcessor = (BeanFactoryPostProcessor) it.next();
factoryProcessor.postProcessBeanFactory(beanFactory);
}
if (logger.isInfoEnabled()) {
if (getBeanDefinitionCount() == 0) {
logger.info("No beans defined in application context [" + getDisplayName() + "]");
}
else {
logger.info(getBeanDefinitionCount() + " beans defined in application context [" + getDisplayName() + "]");
}
}
try {
// **各种BeanFactory处理器
invokeBeanFactoryPostProcessors();
// 注册拦截Bean创建的Bean处理器，这里只是注册，真正调用是在getBean的时候
registerBeanPostProcessors();
// 为上下文初始化Message源，即不同语言的消息体，国际化处理
initMessageSource();
// 初始化应用消息广播器，并放入“applicationEventMulticaster”bean中
/*用户可以在配置文件中为容器定义一个自定义的事件广播器，只要实现ApplicationEventMulticaster就可以了，Spring会通过 反射的机制将其注册成容器的事件广播器，如果没有找到配置的外部事件广播器，Spring自动使用 SimpleApplicationEventMulticaster作为事件广播器。*/
initApplicationEventMulticaster();
// 留给子类来初始化其他bean
onRefresh();
// 在所有注册的bean中查找Listener bean,注册到消息广播器中
/* Spring根据反射机制，使用ListableBeanFactory的getBeansOfType方法，从BeanDefinitionRegistry中找出所有实现 org.springframework.context.ApplicationListener的Bean，将它们注册为容器的事件监听器，实际的操作就是将其添加到事件广播器所提供的监听器注册表中。*/
registerListeners();
// Instantiate singletons this late to allow them to access the message source.
beanFactory.preInstantiateSingletons();
// 最后一步：发布事件
/*在AbstractApplicationContext的publishEvent方法中， Spring委托ApplicationEventMulticaster将事件通知给所有的事件监听器*/
publishEvent(new ContextRefreshedEvent(this));
}
catch (BeansException ex) {
// Destroy already created singletons to avoid dangling resources.
beanFactory.destroySingletons();
throw ex;
}
}
}
刚开始扒源码，感觉挺杂乱的，画画图什么的还是挺有帮助的，昨天就是在一直跟断点，看看要实现我的getBean都走了哪些代码，今天会从整体结构上先看看。