这一部分主要记录bean定义的解析和加载，包括注解方式定义的bean。
【UML】
首先以uml展示ioc过程的全貌，为避免干扰，每个类仅表述了核心的属性，方法和方法内的关键代码。
refresh()方法标橙色，是外部调用的入口，如ContextLoaderListener。
标红色的是一些关键属性和实现。
uml连接： http://dl2.iteye.com/upload/attachment/0115/8766/bedf264c-a530-33b3-924a-2b1799eef3ac.png
【代码解读】
XmlWebApplicationContext继承了AbstractApplicationContext。AbstractApplicationContext的refresh()方法对外提供访问入口，定义了bean定义的解析，创建和一些过程处理，如aop等。使用方法模版的设计模式，由各子类实现一些过程的细节。
@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) {
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
}
}
在refresh()方法中，obtainFreshBeanFactory()方法负责beanFactory的创建及bean定义的解析逻辑，并让applicationContext持有beanFactory。
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
refreshBeanFactory()是一个抽象方法，具体实现是由AbstractRefreshableApplicationContext实现的。在这个方法中，如果已经存在beanFactory，则销毁beanFactory持有的bean定义及bean实例，并销毁beanFactory，代码实现上就是附null。然后创建一个新的beanFactory，具体实现类为DefaultListableBeanFactory。
@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);
}
}
loadBeanDefinitions()方法负责bean定义的解析，在AbstractRefreshableApplicationContext中是个抽象方法，由XmlWebApplicationContext实现。因为我们项目在web.xml配的是XmlWebApplicationContext。在这个方法中，会将beanFacotry以BeanDefinitionRegistry接口的实现放到XmlBeanDefinitionReader中，并让XmlBeanDefinitionReader持有beanFactory，以方便后面解析出beanDefinition后，可以注册到beanFactory中。当然实际持有beanFactory的是XmlBeanDefinitionReader的父类AbstractBeanDefinitionReader，可以参看UML图。
@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);
}
根据在web.xml定义的contextConfigLocation，由XmlBeanDefinitionReader开始解析每个配置文件。整体流程的代码实现在XmlBeanDefinitionReader的父类AbstractBeanDefinitionReader中。但bean定义的解析和加载在XmlBeanDefinitionReader中。
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
String[] configLocations = getConfigLocations();
if (configLocations != null) {
for (String configLocation : configLocations) {
reader.loadBeanDefinitions(configLocation);
}
}
}
实际的bean定义解析也不是由XmlBeanDefinitionReader完成的，XmlBeanDefinitionReader会创建DefaultBeanDefinitionDocumentReader，并将自己作为XmlReaderContext的一个属性，交由DefaultBeanDefinitionDocumentReader进行处理，并由DefaultBeanDefinitionDocumentReader持有XmlReaderContext。
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException
try {
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
finally {
inputStream.close();
}
}
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
documentReader.setEnvironment(this.getEnvironment());
int countBefore = getRegistry().getBeanDefinitionCount();
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}
在DefaultBeanDefinitionDocumentReader解析bean定义的过程中，遇到非http://www.springframework.org/schema/beans命名空间的标签，会交由BeanDefinitionParserDelegate 进行解析。BeanDefinitionParserDelegate会持有DefaultBeanDefinitionDocumentReader的readerContext。
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(this.readerContext, root, parent);
preProcessXml(root);
parseBeanDefinitions(root, this.delegate);
postProcessXml(root);
this.delegate = parent;
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
if (delegate.isDefaultNamespace(root)) {
NodeList nl = root.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (node instanceof Element) {
Element ele = (Element) node;
if (delegate.isDefaultNamespace(ele)) {
parseDefaultElement(ele, delegate);
}
else {
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
类似于注解和aop等的定义解析，都是由BeanDefinitionParserDelegate完成的，他会根据namespaceUri的不同，找到不同的NameSpaceHandler。查找的工作由readerContext持有的属性NamespaceHandlerResolver完成，对应的实现类是DefaultNamespaceHandlerResolver。而DefaultNamespaceHandlerResolver的创建，是在XMLBeanDefinitionReader在创建XmlReaderContext时，就已经指定的，可参考UML图，或者前面的代码解读。
NameSpaceHandler都放在DefaultNamespaceHandlerResolver的属性handlerMappings中，此处找到的实现类是NamespaceHandlerSupport。
public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
String namespaceUri = getNamespaceURI(ele);
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
if (handler == null) {
error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
return null;
}
return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}
NamespaceHandlerSupport的属性parsers中存放了所需的BeanDefinitionParser。以注解为例，会找到ComponentScanBeanDefinitionParser，处理注解的bean定义解析，并最终调用readerContext的fireComponentRegistered方法，向eventListener注册componentDefinition。
@Override
public BeanDefinition parse(Element element, ParserContext parserContext) {
String[] basePackages = StringUtils.tokenizeToStringArray(element.getAttribute(BASE_PACKAGE_ATTRIBUTE),
ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
// Actually scan for bean definitions and register them.
ClassPathBeanDefinitionScanner scanner = configureScanner(parserContext, element);
Set<BeanDefinitionHolder> beanDefinitions = scanner.doScan(basePackages);
registerComponents(parserContext.getReaderContext(), beanDefinitions, element);
return null;
}
protected void registerComponents(
XmlReaderContext readerContext, Set<BeanDefinitionHolder> beanDefinitions, Element element) {
Object source = readerContext.extractSource(element);
CompositeComponentDefinition compositeDef = new CompositeComponentDefinition(element.getTagName(), source);
for (BeanDefinitionHolder beanDefHolder : beanDefinitions) {
compositeDef.addNestedComponent(new BeanComponentDefinition(beanDefHolder));
}
// Register annotation config processors, if necessary.
boolean annotationConfig = true;
if (element.hasAttribute(ANNOTATION_CONFIG_ATTRIBUTE)) {
annotationConfig = Boolean.valueOf(element.getAttribute(ANNOTATION_CONFIG_ATTRIBUTE));
}
if (annotationConfig) {
Set<BeanDefinitionHolder> processorDefinitions =
AnnotationConfigUtils.registerAnnotationConfigProcessors(readerContext.getRegistry(), source);
for (BeanDefinitionHolder processorDefinition : processorDefinitions) {
compositeDef.addNestedComponent(new BeanComponentDefinition(processorDefinition));
}
}
readerContext.fireComponentRegistered(compositeDef);
}
未完，待续 -=^^=-