1、AbstractApplicationContext.refresh的流程：
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2、obtainFreshBeanFactory的調(diào)用棧
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3、主要過(guò)程
resource定位、加載、解析、注冊(cè)、實(shí)例化和依賴(lài)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
創(chuàng)建Resource對(duì)象，然后加載bean
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getResourceByPath
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3.2加載
在XmlBeanDefinitionReader.loadBeanDefinitions(Resource resource)中實(shí)現(xiàn)
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從resource中獲取xml文件的Inputstream，再創(chuàng)建InputSource。真正加載是在doLoadBeanDefinitions里。
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DefaultDocumentReader把xml文件解析為Document
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3.3解析
利用DefaultBeanDefinitionDocumentReader把Document對(duì)象解析為BeanDefinition，最后BeanDefinition對(duì)象集合到封裝類(lèi)BeanDefinitionHolder中
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DefaultBeanDefinitionDocumentReader中實(shí)際解析document的過(guò)程：
1、如果使用<import>元素來(lái)導(dǎo)入外部資源，spring會(huì)首先加載外部資源；
2、如果定義了<Alias>別名，Spring IoC容器將別名元素所定義的別名注冊(cè)到容器中。
3、對(duì)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類(lèi)的parseBeanDefinitionElement方法來(lái)實(shí)現(xiàn)
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BeanDefinitionParseDelegate解析過(guò)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注冊(cè)
在完成BeanDefinition解析并封裝在BeanDefinitionHolder之后，進(jìn)行注冊(cè)
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實(shí)際注冊(cè)過(guò)程由DefaultListableBeanFactory.registerBeanDefinition負(fù)責(zé)
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);
}
}
最終把beanDefinition存放在beanDefinitionMap中，key是beanName，value是beanDefiniton。
4、IoC容器的實(shí)例化與依賴(lài)注入
SimpleInstantiationStrategy提供了兩種方式對(duì)bean進(jìn)行實(shí)例化。第一種是利用反射，第二種是利用CGLIB來(lái)生成。
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5、IoC容器啟動(dòng)(以FileSystemXmlApplicationContext為例)
FileSystemXmlApplicationContext的構(gòu)造函數(shù)如下，啟動(dòng)了IoC容器
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refresh()方法在FileSystemXmlApplicationContext的父類(lèi)AbstractApplicationContext中實(shí)現(xiàn)。在refresh（）方法中，最終調(diào)用了refreshBeanFactory（）方法。
完整IoC容器啟動(dòng)分析（以FileSystemXmlApplicationContext為例）
- FileSystemXmlApplicationContext構(gòu)造方法調(diào)用refresh()方法，這里是載入beanDefinition的入口
- refresh()方法在FileSystemXmlApplicationContext的父類(lèi)AbstractApplicationContext中的實(shí)現(xiàn)，調(diào)用refreshBeanFactory()方法；
- refreshBeanFactory()方法在AbstractApplicationContext的子類(lèi)AbstractRefreshableApplicationContext中實(shí)現(xiàn)，調(diào)用了loadBeanDefinition()方法，啟動(dòng)對(duì)beanDefinition的載入；
- loadBeanDefinition()在AbstractXmlApplicationContext中實(shí)現(xiàn)，調(diào)用了XmlBeanDefinitionReader的loadBeanDefinitions()方法。
- XmlBeanDefinitionReader的loadBeanDefinitions()實(shí)現(xiàn)了對(duì)于承載beanDefnition定義的xml文件的讀入，以I/O的方式。
- 讀入后，對(duì)beanDefinition進(jìn)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的定義解析，在BeanDefinitionParserDelegate.parseBeanDefinitionElement()實(shí)現(xiàn)。
- 最后對(duì)beanDefinition信息進(jìn)行注冊(cè)。就是將每個(gè)beanDefinition以key =beanName,value = beanDefinition放入一個(gè)hashMap中，在DefaultListenableFactoty.RegisterBeanDefinition()中實(shí)現(xiàn)。
經(jīng)過(guò)IoC容器的初始化后，IoC容器持有beanDefintion，為依賴(lài)注入bean即調(diào)用getBean()方法奠定了基礎(chǔ)。
