1、AbstractApplicationContext.refresh的流程：
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2、obtainFreshBeanFactory的调用栈
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3、主要过程
resource定位、加载、解析、注册、实例化和依赖注入
3.1 Resource定位
XmlWebApplicationContext.loadBeanDefinitions(DefaultListableBeanFactory beanFactory)
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XmlWebApplicationContext.loadBeanDefinitions(XmlBeanDefinitionReader reader)
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AbstractBeanDefinitionReader.loadBeanDefinitions
创建Resource对象，然后加载bean
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getResourceByPath
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3.2加载
在XmlBeanDefinitionReader.loadBeanDefinitions(Resource resource)中实现
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从resource中获取xml文件的Inputstream，再创建InputSource。真正加载是在doLoadBeanDefinitions里。
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DefaultDocumentReader把xml文件解析为Document
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3.3解析
利用DefaultBeanDefinitionDocumentReader把Document对象解析为BeanDefinition，最后BeanDefinition对象集合到封装类BeanDefinitionHolder中
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DefaultBeanDefinitionDocumentReader中实际解析document的过程：
1、如果使用<import>元素来导入外部资源，spring会首先加载外部资源；
2、如果定义了<Alias>别名，Spring IoC容器将别名元素所定义的别名注册到容器中。
3、对于既不是<Import>元素，又不是<Alias>元素的元素，即Spring配置文件中普通的<Bean>元素的解析由BeanDefinitionParserDelegate类的parseBeanDefinitionElement方法来实现
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BeanDefinitionParseDelegate解析过程
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
String id = ele.getAttribute(ID_ATTRIBUTE);
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
List<String> aliases = new ArrayList<String>();
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}
String beanName = id;
if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
beanName = aliases.remove(0);
if (logger.isDebugEnabled()) {
logger.debug("No XML 'id' specified - using '" + beanName +
"' as bean name and " + aliases + " as aliases");
}
}
if (containingBean == null) {
checkNameUniqueness(beanName, aliases, ele);
}
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
if (!StringUtils.hasText(beanName)) {
try {
if (containingBean != null) {
beanName = BeanDefinitionReaderUtils.generateBeanName(
beanDefinition, this.readerContext.getRegistry(), true);
}
else {
beanName = this.readerContext.generateBeanName(beanDefinition);
// Register an alias for the plain bean class name, if still possible,
// if the generator returned the class name plus a suffix.
// This is expected for Spring 1.2/2.0 backwards compatibility.
String beanClassName = beanDefinition.getBeanClassName();
if (beanClassName != null &&
beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
aliases.add(beanClassName);
}
}
if (logger.isDebugEnabled()) {
logger.debug("Neither XML 'id' nor 'name' specified - " +
"using generated bean name [" + beanName + "]");
}
}
catch (Exception ex) {
error(ex.getMessage(), ele);
return null;
}
}
String[] aliasesArray = StringUtils.toStringArray(aliases);
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
return null;
}
3.4注册
在完成BeanDefinition解析并封装在BeanDefinitionHolder之后，进行注册
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实际注册过程由DefaultListableBeanFactory.registerBeanDefinition负责
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException {
Assert.hasText(beanName, "Bean name must not be empty");
Assert.notNull(beanDefinition, "BeanDefinition must not be null");
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
BeanDefinition oldBeanDefinition;
oldBeanDefinition = this.beanDefinitionMap.get(beanName);
if (oldBeanDefinition != null) {
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
"': There is already [" + oldBeanDefinition + "] bound.");
}
else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (this.logger.isWarnEnabled()) {
this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
"' with a framework-generated bean definition: replacing [" +
oldBeanDefinition + "] with [" + beanDefinition + "]");
}
}
else if (!beanDefinition.equals(oldBeanDefinition)) {
if (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
if (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList<String>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
if (this.manualSingletonNames.contains(beanName)) {
Set<String> updatedSingletons = new LinkedHashSet<String>(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
// Still in startup registration phase
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (oldBeanDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
}
最终把beanDefinition存放在beanDefinitionMap中，key是beanName，value是beanDefiniton。
4、IoC容器的实例化与依赖注入
SimpleInstantiationStrategy提供了两种方式对bean进行实例化。第一种是利用反射，第二种是利用CGLIB来生成。
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5、IoC容器启动(以FileSystemXmlApplicationContext为例)
FileSystemXmlApplicationContext的构造函数如下，启动了IoC容器
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refresh()方法在FileSystemXmlApplicationContext的父类AbstractApplicationContext中实现。在refresh（）方法中，最终调用了refreshBeanFactory（）方法。
完整IoC容器启动分析（以FileSystemXmlApplicationContext为例）
- FileSystemXmlApplicationContext构造方法调用refresh()方法，这里是载入beanDefinition的入口
- refresh()方法在FileSystemXmlApplicationContext的父类AbstractApplicationContext中的实现，调用refreshBeanFactory()方法；
- refreshBeanFactory()方法在AbstractApplicationContext的子类AbstractRefreshableApplicationContext中实现，调用了loadBeanDefinition()方法，启动对beanDefinition的载入；
- loadBeanDefinition()在AbstractXmlApplicationContext中实现，调用了XmlBeanDefinitionReader的loadBeanDefinitions()方法。
- XmlBeanDefinitionReader的loadBeanDefinitions()实现了对于承载beanDefnition定义的xml文件的读入，以I/O的方式。
- 读入后，对beanDefinition进行解析。Bean解析采用SAX工具，先按照XML文件格式解析，再按照spring bean的定义解析，在BeanDefinitionParserDelegate.parseBeanDefinitionElement()实现。
- 最后对beanDefinition信息进行注册。就是将每个beanDefinition以key =beanName,value = beanDefinition放入一个hashMap中，在DefaultListenableFactoty.RegisterBeanDefinition()中实现。
经过IoC容器的初始化后，IoC容器持有beanDefintion，为依赖注入bean即调用getBean()方法奠定了基础。
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