容器的功能扩展
1、概述
之前的文章中BeanFactory接口以及它的默认实现类XmlBeanFactory为例进行分析，但是Spring中还提供了另一个接口ApplicationContext，用于扩展BeanFactory中现有的功能。
ApplicationContext和BeanFactory两者都是用于加载Bean的，但是相比之下，ApplicationContext提供了更多的扩展功能，简而言之：ApplicationContext包含BeanFactory的所有功能。通常建议比优先使用ApplicationContext
我们就以ClassPathXmlApplicationContext作为切入点，开始对整体功能进行分析，代码如下：
/**
* Create a new ClassPathXmlApplicationContext with the given parent,
* loading the definitions from the given XML files.
* @param configLocations array of resource locations
* @param refresh whether to automatically refresh the context,
* loading all bean definitions and creating all singletons.
* Alternatively, call refresh manually after further configuring the context.
* @param parent the parent context
* @throws BeansException if context creation failed
* @see #refresh()
*/
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}2、设置路径（ setConfigLocations(configLocations);）
/**
* Set the config locations for this application context.
* <p>If not set, the implementation may use a default as appropriate.
*/
public void setConfigLocations(String... locations) {
if (locations != null) {
Assert.noNullElements(locations, "Config locations must not be null");
this.configLocations = new String[locations.length];
for (int i = 0; i < locations.length; i++) {
this.configLocations[i] = resolvePath(locations[i]).trim();
}
}
else {
this.configLocations = null;
}
}
3、扩展功能refresh();
refresh函数中包含了几乎ApplicationContext中提供的全部功能.
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
logger.warn("Exception encountered during context initialization - cancelling refresh attempt", ex);
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
}
}
我们简单的分析下代码的步骤：
（1）初始化前的准备工作，例如对系统属性或者环境变量进行准备及验证。
在某种情况下项目的使用需要读取某些系统变量，而这个变量的设置很可能会影响着系统的正确性，那么ClassPathXmlApplicationContext为我们提供的这个准备函数就显得非常必要，他可以在spring启动的时候提前对必须的环境变量进行存在性验证。
（2）初始化BeanFactory，并进行XML文件读取。
之前提到ClassPathXmlApplicationContext包含着对BeanFactory所提供的一切特征，那么这一步中将会复用BeanFactory中的配置文件读取解析其他功能，这一步之后ClassPathXmlApplicationContext实际上就已经包含了BeanFactory所提供的功能，也就是可以进行Bean的提取等基本操作了。
（3）对BeanFactory进行各种功能填充
@Qualifier和@Autowired应该是大家非常熟悉的注解了，那么这两个注解正是在这一步骤中增加支持的。
（4）子类覆盖方法做额外处理。
（5）激活各种BeanFactory处理器
（6）注册拦截bean创建的bean处理器，这里只是注册，真正的调用是在getBean时候
（7）为上下文初始化Message源
（8）初始化应用消息广播器，并放入“applicationEventMulticaster”bean中
（9）留给子类来初始化其他的bean
（10）在所有注册的bean中查找listener bean，注册到消息广播器中
（11）初始化剩下的单实例（非惰性的）
（12）完成刷新过程，通知生命周期处理器lifecycleProcessor刷新过程，同时发出ContextRefreshEvent通知别人。
接下来我们就详细的讲解每一个过程：
4、环境准备prepareRefresh();
/**
* Prepare this context for refreshing, setting its startup date and
* active flag as well as performing any initialization of property sources.
*/
protected void prepareRefresh() {
this.startupDate = System.currentTimeMillis();
this.active.set(true);
if (logger.isInfoEnabled()) {
logger.info("Refreshing " + this);
}
// Initialize any placeholder property sources in the context environment
initPropertySources();
// Validate that all properties marked as required are resolvable
// see ConfigurablePropertyResolver#setRequiredProperties
getEnvironment().validateRequiredProperties();
} (1) initPropertySources，这正符合Spring的开放式结构设计，给用户最大扩展Spring的能力。用户可以根据自身的需要重写initPropertySourece方法，并在方法中进行个性化的属性处理及设置。
（2）validateRequiredProperties则是对属性进行验证
5、加载BeanFactory()(obtainFreshBeanFactory()方法)
/**
* Tell the subclass to refresh the internal bean factory.
* @return the fresh BeanFactory instance
* @see #refreshBeanFactory()
* @see #getBeanFactory()
*/
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}核心在refreshBeanFactory方法中，方法的实现是在AbstractRefreshableApplicationContext中：
/**
* This implementation performs an actual refresh of this context's underlying
* bean factory, shutting down the previous bean factory (if any) and
* initializing a fresh bean factory for the next phase of the context's lifecycle.
*/
@Override
protected final void refreshBeanFactory() throws BeansException {
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
customizeBeanFactory(beanFactory);
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
我们详细分析下上面代码的步骤：
（1）创建DefaultListableBeanFactory
以前我们分析BeanFactory的时候，不知道是否还有印象，声明方式为：BeanFactory bf = new XmlBeanFactory(“beanFactoryTest.xml”)，其中的XmlBeanFactory继承自DefaulltListableBeanFactory;，并提供了XmlBeanDefinitionReader类型的reader属性，也就是说DefaultListableBeanFactory是容器的基础。必须首先要实例化，这里就是创建DefaultListableBeanFactory的步骤。
（2）指定序列号ID
（3）定制BeanFactory
（4）加载BeanDefinition
（5）使用全局变量保存BeanFactory
因为DefaultListableBeanFactory类型的变量beanFactory是函数内部的局部变量， 所以要使用全局变量记录解析结果
5.1 定制BeanFactory（通过customizeBeanFactory(beanFactory);）
/**
* Customize the internal bean factory used by this context.
* Called for each {@link #refresh()} attempt.
* <p>The default implementation applies this context's
* {@linkplain #setAllowBeanDefinitionOverriding "allowBeanDefinitionOverriding"}
* and {@linkplain #setAllowCircularReferences "allowCircularReferences"} settings,
* if specified. Can be overridden in subclasses to customize any of
* {@link DefaultListableBeanFactory}'s settings.
* @param beanFactory the newly created bean factory for this context
* @see DefaultListableBeanFactory#setAllowBeanDefinitionOverriding
* @see DefaultListableBeanFactory#setAllowCircularReferences
* @see DefaultListableBeanFactory#setAllowRawInjectionDespiteWrapping
* @see DefaultListableBeanFactory#setAllowEagerClassLoading
*/
protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {
if (this.allowBeanDefinitionOverriding != null) {
beanFactory.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}
if (this.allowCircularReferences != null) {
beanFactory.setAllowCircularReferences(this.allowCircularReferences);
}
}5.2 加载BeanFactory（通过loadBeanDefinitions(beanFactory);实现）
/**
* Loads the bean definitions via an XmlBeanDefinitionReader.
* @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
* @see #initBeanDefinitionReader
* @see #loadBeanDefinitions
*/
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
beanDefinitionReader.setEnvironment(getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
initBeanDefinitionReader(beanDefinitionReader);
loadBeanDefinitions(beanDefinitionReader);
}除了初始化DefaultListableBeanFactory外，还需要XmlBeanDefinitionReader来读取XML，那么在loadBeanDefinitions方法中首先要做的就是初始化XmlBeanDefinitonReader。在初始化了DefaultListableBeanFactory和XmlBeanDefinitionReader后，就可以进行配置文件的读取了。继续进入到loadBeanDefinitions(beanDefinitionReader)方法体中，代码如下：
/**
* Load the bean definitions with the given XmlBeanDefinitionReader.
* <p>The lifecycle of the bean factory is handled by the refreshBeanFactory method;
* therefore this method is just supposed to load and/or register bean definitions.
* <p>Delegates to a ResourcePatternResolver for resolving location patterns
* into Resource instances.
* @throws IOException if the required XML document isn't found
* @see #refreshBeanFactory
* @see #getConfigLocations
* @see #getResources
* @see #getResourcePatternResolver
*/
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
String[] configLocations = getConfigLocations();
if (configLocations != null) {
for (String configLocation : configLocations) {
reader.loadBeanDefinitions(configLocation);
}
}
}
因为在XmlBeanDefinitionReader中已经将之前初始化的DefaultListableBeanFactory注册进去了，所以XmlBeanDefinitionReader所读取的BeanDefinitionHolder都会注册到DefinitionListableBeanFactory中，也就是经过这个步骤，DefaultListableBeanFactory的变量beanFactory已经包含了所有解析好的配置。
6、功能扩展
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
/**
* Configure the factory's standard context characteristics,
* such as the context's ClassLoader and post-processors.
* @param beanFactory the BeanFactory to configure
*/
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
beanFactory.setBeanClassLoader(getClassLoader());
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
// BeanFactory interface not registered as resolvable type in a plain factory.
// MessageSource registered (and found for autowiring) as a bean.
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
// Detect a LoadTimeWeaver and prepare for weaving, if found.
if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
// Set a temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
// Register default environment beans.
if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
}
if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
}
if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
}
}
详细分析下代码发现上面函数主要是在以下方法进行了扩展：
（1）对SPEL语言的支持
（2）增加对属性编辑器的支持
（3）增加对一些内置类的支持，如EnvironmentAware、MessageSourceAware的注入
（4）设置了依赖功能可忽略的接口
（5）注册一些固定依赖的属性
（6）增加了AspectJ的支持
（7）将相关环境变量及属性以单例模式注册
接下来分析下以上步骤。
6.1 增加对SPEL语言的支持
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));6.2 增加属性编辑器
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));7、设置忽略依赖
// Configure the bean factory with context callbacks.
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
8、注册依赖
// BeanFactory interface not registered as resolvable type in a plain factory.
// MessageSource registered (and found for autowiring) as a bean.
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
9、BeanFactory的后处理