本文通过FileSystemXmlApplicationContext来分析spring的初始化过程，下面是
FileSystemXmlApplicationContext继承关系图
测试程序的Bean和配置文件如下
public class TestBean {
public TestBean(List<String> testList){
System.out.println(testList.size());
}
public void print(){
System.out.println("bean run...");
}
}
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="TestBean" class="test.TestBean" name="BeanName">
<constructor-arg >
<list>
<value>zhanglun</value>
<value>zhanglun111</value>
</list>
</constructor-arg>
</bean>
</beans>入口主函数如下，通过main函数作为入口，对spring源码进行调试分析
public class MaiClass {
public static void main(String[] args){
FileSystemXmlApplicationContext fileSystemXmlApplicationContext =
new FileSystemXmlApplicationContext("classpath:spring-config.xml");
TestBean testBean = (TestBean) fileSystemXmlApplicationContext.getBean("TestBean");
testBean.print();
}
}进入FileSystemXmlApplicationContext的构造方法，FileSystemXmlApplicationContext通过refresh方法对上下文对象就行初始化，完成BeanDefinitions的定位、载入和注册
public FileSystemXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}具体refresh方法的实现，参照FileSystemXmlApplicationContext的父类AbstractApplicationContext
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
//这里是在子类中启动refreshBeanFactory的地方
// 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);//设置beanFacory的后置处理
//调用BeanFatory的后置处理器，这些后置处理器是在Bean定义中向容器注册的
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
//注册bean的后置处理器，在Bean创建过程中调用
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
//对上下文中的消息源进行初始化
// Initialize message source for this context.
initMessageSource();
//初始化上下文中的事件机制
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
//初始化其他特殊的Bean
// Initialize other special beans in specific context subclasses.
onRefresh();
//检查监听Bean并将这些Bean像容器中注册
// Check for listener beans and register them.
registerListeners();
//初始化所有的(non-lazy-init)单件
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
//发布容器事件，结束Refresh过程
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
//防止Bean资源占用，在异常处理中，销毁已经在前面过程中生成的单件Bean
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
//重置active标志
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}我们主要关注obtainFreshBeanFactory方法，此方法完成BeanDefinitions在BeanFactory中的定位、载入、注册，并返回ConfigurableListableBeanFactory对象，下面查看AbstractApplictionContext的obtainFreshBeanFactory方法实现
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();//beanFactory是个成员变量
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}查看AbstractRefreshableApplicationContext中refreshBeanFactory方法
protected final void refreshBeanFactory() throws BeansException {
if (hasBeanFactory()) {//判断，如果已经建立了BeanFactory，则销毁并关闭
destroyBeans();
closeBeanFactory();
}
try {//创建并设置持有的DefaultListableBeanFactory，调用loadBeanDefinitions载入BeanDefinition
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
customizeBeanFactory(beanFactory);
loadBeanDefinitions(beanFactory);//启动BeanDefinition的载入
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}refreshBeanFactory调用loadBeanDefinitions方法进行BeanDefinitions的定位载入和注册，具体实现参照AbstractXmlApplicationContext，此方法完成对beanDefinitionReader的初始化，并将beanFactory注入到DefinitionReader中去
@Override//这里是实现loadBeanDefinitions的地方
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
//创建XmlBeanDefinitionReader，并通过回调设置到BeanFactory中去
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// 这里设置beanDefinitionReader，为XmlBeanDefinitionReader配
// ResourceLoader，因为DefaultResourceLoader是父类，所以this直接被使用
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);//把FileSystemXmlApplicationContext注册到reader
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
//这里是启动Bean信息的载入过程
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
initBeanDefinitionReader(beanDefinitionReader);
loadBeanDefinitions(beanDefinitionReader);
}继续查看最后一行的loadBeanDefinitions(XmlBeanDefinitionReader reader)方法
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
Resource[] configResources = getConfigResources();//以Resource方式获得配置文件定位
if (configResources != null) {
reader.loadBeanDefinitions(configResources);
}
String[] configLocations = getConfigLocations();//以String方式获得配置文件定位
if (configLocations != null) {
reader.loadBeanDefinitions(configLocations);
}
}具体对BeanDefinition的操作，有BeanDefinitionReader完成，查看reader.loadBeanDefinitions方法，具体实现参照AbstractBeanDefinitionReader，此方法得到Resource对象，调用XMLBeanDefinitionReader，载入XML形式的BeanDefinition
//这里是载入xml形式的BeanDefinition的地方
public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
ResourceLoader resourceLoader = getResourceLoader();//取得ResourceLoader，使用的是DefaultResourceLoader
if (resourceLoader == null) {
throw new BeanDefinitionStoreException(
"Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
}
// 对resource路径模式进行解析，actualResources Resource集合，只想我们已经定义好的BeanDefinitions信息，可以是多个文件
if (resourceLoader instanceof ResourcePatternResolver) {
//
try {//调用getResources完成具体Resource定位
Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
int loadCount = loadBeanDefinitions(resources);//!!载入XML形式的BeanDefinition
if (actualResources != null) {
for (Resource resource : resources) {
actualResources.add(resource);
}
}
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
}
return loadCount;
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"Could not resolve bean definition resource pattern [" + location + "]", ex);
}
}
else {
// 调用resourceLoader完成具体Resource定位
Resource resource = resourceLoader.getResource(location);
int loadCount = loadBeanDefinitions(resource);//取得Resource的具体过程
if (actualResources != null) {
actualResources.add(resource);
}
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
}
return loadCount;
}
}查看XmlBeanDefinitionReader的loadBeanDefinitions方法，此方法获取xml文件inputSource对象，inputSource封装了io对象等
//这里是载入XML形式的BeanDefinition的地方
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isInfoEnabled()) {
logger.info("Loading XML bean definitions from " + encodedResource.getResource());
}
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {
currentResources = new HashSet<EncodedResource>(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
}
try {//这里得到xml文件，并得到io的inputSource准备进行读取
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();
}
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"IOException parsing XML document from " + encodedResource.getResource(), ex);
}
finally {
currentResources.remove(encodedResource);
if (currentResources.isEmpty()) {
this.resourcesCurrentlyBeingLoaded.remove();
}
}
}继续查看XmlBeanDefinitionReader的doLoadBeanDefinitions方法，此方法获取Document对象，并调用registerBeanDefinitions对BeanDefinition进行解析
//具体的读取过程可以在doLoadBeanDefinitions中找到，这是从特定的xml中载入BeanDefinition的地方
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {//取的xml的Document对象，这个解析过程是由documentLoader完成的
Document doc = doLoadDocument(inputSource, resource);
return registerBeanDefinitions(doc, resource);//这里是对BeanDefinetion解析的详细过程，这个过程会使用到Spring的Bean配置规则
}
catch (BeanDefinitionStoreException ex) {
throw ex;
}
catch (SAXParseException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
}
catch (SAXException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"XML document from " + resource + " is invalid", ex);
}
catch (ParserConfigurationException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Parser configuration exception parsing XML from " + resource, ex);
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"IOException parsing XML document from " + resource, ex);
}
catch (Throwable ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Unexpected exception parsing XML document from " + resource, ex);
}
}继续查看XmlBeanDefinitionReader的registerBeanDefinitions方法，此方法产生documentReader对象，调用documentReader的registerBeanDefinitions方法注入documentReader上下文对象，并对BeanDefinition进行解析。createReaderContext(resource)方法返回XmlReaderContext对象，其中包含Resource信息，和XmlBeanDefinitionReader的对象信息，从而也包含BeanFactory和applicationContext对象信息（在XmlBeanDefinitionReader中）
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();//得到BeanDefinitionDocumentReader对来自XML的Beandefinition进行解析
int countBefore = getRegistry().getBeanDefinitionCount();
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));//具体解析过程在registerBeanDefinitions完成
return getRegistry().getBeanDefinitionCount() - countBefore;//createReaderContext(resource),返回documentReader上下文对象，包含次BeanDefinitionReader，进而注入BeanFactory和applicationContext
}继续查看DefaultBeanDefinitionDocumentReader的RegisterBeanDefinitions方法
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public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
Element root = doc.getDocumentElement();
doRegisterBeanDefinitions(root);
}继续查看DefaultBeanDefinitionDocumentReader的doRegisterBeanDefinitions方法，此方法获取BeanDefinitionParserDelegate，同时将XmlReaderContext注入到BeanDefinitionParserDelegate中
protected void doRegisterBeanDefinitions(Element root) {
// Any nested <beans> elements will cause recursion in this method. In
// order to propagate and preserve <beans> default-* attributes correctly,
// keep track of the current (parent) delegate, which may be null. Create
// the new (child) delegate with a reference to the parent for fallback purposes,
// then ultimately reset this.delegate back to its original (parent) reference.
// this behavior emulates a stack of delegates without actually necessitating one.
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(getReaderContext(), root, parent);
if (this.delegate.isDefaultNamespace(root)) {
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
if (StringUtils.hasText(profileSpec)) {
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
if (logger.isInfoEnabled()) {
logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +
"] not matching: " + getReaderContext().getResource());
}
return;
}
}
}
preProcessXml(root);
parseBeanDefinitions(root, this.delegate);
postProcessXml(root);
this.delegate = parent;
}继续查看DefaultBeanDefinitionDocumentReader的parseBeanDefinitions方法，此方法遍历xml根节点下每一个子节点，每个子节点对应一个BeanDefinition对象
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); } }
查看DefaultBeanDefinitionDocumentReader的parseDefaultElement方法，此方法判断子节点的类型，进行相应的解析如果是<bean>标签，执行processBeanDefinition方法
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);//!!
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}查看DefaultBeanDefinitionDocumentReader的processBeanDefinition的processBeanDefinition方法，
此方法调用BeanDefinitionParserDelegate对XML子标签元素进行具体的解析，产生BeanDefinition对象并封装的BeanDefinitionHolder对象中去，然后调用registerBeanDefinition方法，将BeanDefinition载入到ApplicationContext中去。
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {//BeanDefinitionHolder是BeanDefinition的封装类，封装了BeanDefinition，Bean的名字和别名，用它来完成像IOC容器注册
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// 这里是向IOC溶剂注册解析到的BeanDefinition的地方
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// 在BeanDefinition像IOC容器注册完之后，发送消息
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}下面查看BeanDefinitionParserDelegate的parseBeanDefinitionElement，此方法解析了xml中子标签，并产生BeanDefinition对象，连同alias等信息，一同封装在BeanDefinitionHolder中，具体读取xml标签操作，还需读者自行阅读源码
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
String id = ele.getAttribute(ID_ATTRIBUTE);//取的bean的id、name、alias
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);//检查bean的那么是否有重复
}
//这个方法会引发对bean元素的详细解析
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;
}产生BeanDefinitionHolder对象后，调用BeanDefinitionReaderUtils.registerBeanDefinition将BeanDefinition对象注入到BeanFactory中去，该方法registry参数实际为DefaultListableBeanFactory，DefaultListableBeanFactory中有一个HashMap来存储BeanDefinition
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
// Register bean definition under primary name.
String beanName = definitionHolder.getBeanName();
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// Register aliases for bean name, if any.
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);
}
}
}此时查看DefaultListableBeanFactory的registerBeanDefinition方法，此方法执行完，则BeanFactory的定位、载入和注册已经完成
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;
//这里检查是不是有相同名字的BeanDefinition已经在IOC容器中注册了，如果有相同名字的，但又不允许覆盖，则抛出异常
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);
}
}