本文深入解析Spring框架中IOC容器加载和解析bean配置文件的过程，从ClassPathXmlApplicationContext构造方法开始，详细介绍了bean定义的加载、解析和注册机制。
本文主要内容及做什么
主要针对spring中的ioc，采用debug方式讲解spring如何加载bean配置文件，目的是对加载过程有个大概了解，spring源码优雅且复杂。
项目环境
spring版本号为4.0.2，jdk1.8。
spring配置文件代码：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:util="http://www.springframework.org/schema/util"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.0.xsd">
<bean id="person" class="com.test.service.PersonServiceImpl">
<property name="name" value="hello spring"></property>
</bean>
</beans>
test代码为：
public class test {
public static void main(String[] args) {
ApplicationContext cx = new ClassPathXmlApplicationContext("applicationContext.xml");
PersonServiceImpl obj = cx.getBean(PersonServiceImpl.class);
System.out.println(obj.toString());
}
}
从上面可以看出，spring从拿到资源文件到创建并获取bean，从开发角度只需要两行代码可实现，但了解其内部原理也很重要，下面开始调试，断点进入 ApplicationContext cx = new ClassPathXmlApplicationContext("applicationContext.xml"); 这一行代码。
1、按F5进入，进入到 ClassPathXmlApplicationContext 类的构造方法，方法第一行 super(parent); 调用了父类的构造方法，父类为AbstractXmlApplicationContext，父类构造方法中同样super(parent)继续调用其父类，同样的方式分别调用了AbstractRefreshableConfigApplicationContext，AbstractApplicationContext，DefaultResourceLoader；一直调用父类构造方法，初始化了一个空的ApplicationContext对象。
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}
2、setConfigLocations(configLocations) 方法主要是解析spring的配置文件地址，并赋值到成员变量 private String[] configLocations 中，可以看到为数组类型，可配置多个。
3、进入 ClassPathXmlApplicationContext 类的 refresh() 方法，ClassPathXmlApplicationContext 类本身没实现refresh() 方法，而是继承了其父类 AbstractApplicationContext 中的refresh() 方法，AbstractApplicationContext 是一个抽象类，refresh()是ApplicationContext初始化的核心，包含了初始化BeanFactory，解析XML加载BeanDefinition，注册bean处理器，注册事件添加监听等，以下为其refresh()代码：
@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;
}
}
}
4、进入refresh()方法中的prepareRefresh()方法，主要是做些准备工作，记录开始时间，环境准备等。
/**
* 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();
synchronized (this.activeMonitor) {
this.active = 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();
}
5、进入 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory() ，创建一个beanFactory，并且解析xml中的bean定义，放置在bean工厂当中，obtainFreshBeanFactory()方法代码：
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
6、进入refreshBeanFactory()方法，是在 AbstractRefreshableApplicationContext 抽象类中，代码：
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);
}
}
它主要完成如下：
1）hasBeanFactory()判断当前context是否持有beanFactory，如果已经存在则销毁所有单例Bean的实例，再把当前beanFactory设置为null；
2）createBeanFactory()初始化新的beanFactory，类型为DefaultListableBeanFactory；
3）customizeBeanFactory(beanFactory)设定beanFactory的一些属性；
4）loadBeanDefinitions(beanFactory)加载BeanDefinitions，这是最为核心的一步
7、进入 DefaultListableBeanFactory beanFactory = createBeanFactory() 方法，直接新创建了一个 DefaultListableBeanFactory类型的beanFactory并且返回，在创建的同时初始化存放bean相关属性的缓存，一般都是使用Hahsmap或者ConcurrentHashMap；
protected DefaultListableBeanFactory createBeanFactory() {
return new DefaultListableBeanFactory(getInternalParentBeanFactory());
}
8、返回来进入 refreshBeanFactory() 方法中关键的方法 loadBeanDefinitions(beanFactory)，在抽象类 AbstractXmlApplicationContext 中，传入了创建好的beanFactory，代码：
/**
* 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(this.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);
}
9、来看 XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory) 这行代码，新建读取器 XmlBeanDefinitionReader，Reader是用来读取并解析xml文件，XmlBeanDefinitionReader 为抽象类，XmlBeanDefinitionReader 实现了 BeanDefinitionReader 接口，覆写了loadBeanDefinitions方法。
10、进入关键方法 loadBeanDefinitions(beanDefinitionReader)：
/**
* Load the bean definitions with the given XmlBeanDefinitionReader.
* <p>The lifecycle of the bean factory is handled by the {@link #refreshBeanFactory}
* method; hence this method is just supposed to load and/or register bean definitions.
* @param reader the XmlBeanDefinitionReader to use
* @throws BeansException in case of bean registration errors
* @throws IOException if the required XML document isn't found
* @see #refreshBeanFactory
* @see #getConfigLocations
* @see #getResources
* @see #getResourcePatternResolver
*/
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
Resource[] configResources = getConfigResources();
if (configResources != null) {
reader.loadBeanDefinitions(configResources);
}
String[] configLocations = getConfigLocations();
if (configLocations != null) {
reader.loadBeanDefinitions(configLocations);
}
}
注解说的是用 XmlBeanDefinitionReader 读取器加载bean定义，其中出现了两重载方法loadBeanDefinitions()，来看下getConfigResources()方法是怎么定义的：
ClassPathXmlApplicationContext 类中的方法：
protected Resource[] getConfigResources() {
return this.configResources;
}
AbstractRefreshableConfigApplicationContext 为 ClassPathXmlApplicationContext 父类，
AbstractRefreshableConfigApplicationContext 抽象类中的方法：
protected String[] getConfigLocations() {
return (this.configLocations != null ? this.configLocations : getDefaultConfigLocations());
}
可以看到是获取 ApplicationContext 子类的常量值，所以，到底是configLocations 还是configResources ，与最初实例化ClassPathXmlApplicationContext 对象选择的构造方法相关，实例化 applicationContext 对象的方式是new ClassPathXmlApplicationContext(“applicationContext.xml”)，那么setConfigLocations方法就会被调用：
String[] configLocations = getConfigLocations();
if (configLocations != null) {
reader.loadBeanDefinitions(configLocations);
}
11、进入 reader.loadBeanDefinitions(configLocations) 方法，进入了 AbstractBeanDefinitionReader 抽象类，它为XmlBeanDefinitionReader 类的父类，
public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
Assert.notNull(locations, "Location array must not be null");
int counter = 0;
for (String location : locations) {
counter += loadBeanDefinitions(location);
}
return counter;
}
这个方法返回值为所找到的bean定义的个数，但是这里可以看出，在调用它的方法内并没有接收和使用这个返回值。
在最初设定的资源路径为classpath下的applicationContext.xml，所以这个方法的参数值为[applicationContext.xml]
12，进入loadBeanDefinitions(location)方法：
public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {
return loadBeanDefinitions(location, null);
}
再进去：
public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
ResourceLoader resourceLoader = getResourceLoader();
if (resourceLoader == null) {
throw new BeanDefinitionStoreException(
"Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
}
if (resourceLoader instanceof ResourcePatternResolver) {
// Resource pattern matching available.
try {
Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
int loadCount = loadBeanDefinitions(resources);
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 {
// Can only load single resources by absolute URL.
Resource resource = resourceLoader.getResource(location);
int loadCount = loadBeanDefinitions(resource);
if (actualResources != null) {
actualResources.add(resource);
}
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
}
return loadCount;
}
}
首先getResourceLoader()获取初始化applicationcontext过程中设置的资源加载器，断定是否为ResourcePatternResolver类型。
进入if中的 loadBeanDefinitions(resources) 方法：
public int loadBeanDefinitions(Resource... resources) throws BeanDefinitionStoreException {
Assert.notNull(resources, "Resource array must not be null");
int counter = 0;
for (Resource resource : resources) {
counter += loadBeanDefinitions(resource);
}
return counter;
}
13，进入loadBeanDefinitions()，发现从AbstractBeanDefinitionReader 抽象类跳到 XmlBeanDefinitionReader 类，AbstractBeanDefinitionReader 为 XmlBeanDefinitionReader 的父类：
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
return loadBeanDefinitions(new EncodedResource(resource));
}
上述代码把Resource对象包装成EncodedResource对象，
再进到 loadBeanDefinitions() 方法中：
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 {
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();
}
}
}
上述方法中获取了资源的InputSource源，InputSource类为处理XML文件辅助类
14、进入 doLoadBeanDefinitions(inputSource, encodedResource.getResource()) 方法：
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
Document doc = doLoadDocument(inputSource, resource);
return registerBeanDefinitions(doc, resource);
}
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);
}
}
doLoadDocument(inputSource, resource) 方法返回的资源的Document对象
15，进入 registerBeanDefinitions(doc, resource) 方法中：
/**
* Register the bean definitions contained in the given DOM document.
* Called by {@code loadBeanDefinitions}.
* <p>Creates a new instance of the parser class and invokes
* {@code registerBeanDefinitions} on it.
* @param doc the DOM document
* @param resource the resource descriptor (for context information)
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of parsing errors
* @see #loadBeanDefinitions
* @see #setDocumentReaderClass
* @see BeanDefinitionDocumentReader#registerBeanDefinitions
*/
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;
}
看注解，Register the bean definitions contained in the given DOM document，从给定的dom对象中注册bean定义。
首先创建了 BeanDefinitionDocumentReader 对象，BeanDefinitionDocumentReader类有两个作用，完成 BeanDefinition 的解析和注册。
int countBefore = getRegistry().getBeanDefinitionCount()获取先前存在的BeanDefinition个数，用于计算新注册的BeanDefinition个数。
进入 getBeanDefinitionCount() 方法，DefaultListableBeanFactory类中的getBeanDefinitionCount()方法：
public int getBeanDefinitionCount() {
return this.beanDefinitionMap.size();
}
/** Map of bean definition objects, keyed by bean name */
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(64);
beanDefinitionMap是个ConcurrentHashMap，用于存放bean，key为String类型，value为BeanDefinition类型，BeanDefinition是一个接口，具有很多类型的实现子类，spring默认使用其子类GenericBeanDefinition，GenericBeanDefinition属性很少，大部分的继承自AbstractBeanDefinition类。至于 DefaultListableBeanFactory 类，很多人都说 DefaultListableBeanFactory 是spring ioc最为核心的类，说它是spring ioc的发动机，聚集了ioc大部分核心公共方法和受保护的方法。
由于之前没有注册过BeanDefinition，所以countBefore值为0。
16、进入documentReader.registerBeanDefinitions(doc, createReaderContext(resource))：
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
Element root = doc.getDocumentElement();
doRegisterBeanDefinitions(root);
}
获取了dom对象的root根元素。
17、进入 doRegisterBeanDefinitions() 方法：
/**
* Register each bean definition within the given root {@code <beans/>} element.
* @throws IllegalStateException if {@code <beans profile="..."} attribute is present
* and Environment property has not been set
* @see #setEnvironment
*/
protected void doRegisterBeanDefinitions(Element root) {
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
if (StringUtils.hasText(profileSpec)) {
Assert.state(this.environment != null, "Environment must be set for evaluating profiles");
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
if (!this.environment.acceptsProfiles(specifiedProfiles)) {
return;
}
}
// 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(this.readerContext, root, parent);
preProcessXml(root);
parseBeanDefinitions(root, this.delegate);
postProcessXml(root);
this.delegate = parent;
}
18、parseBeanDefinitions 方法传入了资源文件的根元素和新建的代理对象，进入 parseBeanDefinitions(root, this.delegate)：
/**
* Parse the elements at the root level in the document:
* "import", "alias", "bean".
* @param root the DOM root element of the document
*/
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);
}
}
parseDefaultElement 是对根元素一步一步解析，当解析到定义好的<bean>元素时，node即为Element，强制转换为Element，进入了元素解析 parseDefaultElement(ele, delegate) 方法。
19、进入parseDefaultElement(ele, delegate)：
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);
}
}
这里判断资源文件中设置bean格式，最初是用普通bean定义的形式，BEAN_ELEMENT的值为"bean"。
20、进入processBeanDefinition(ele, delegate)：
/**
* Process the given bean element, parsing the bean definition
* and registering it with the registry.
*/
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// Send registration event.
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
利用代理对象创建了一个BeanDefinition持有者，作为参数。
21、进入 BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry())：
/**
* Register the given bean definition with the given bean factory.
* @param definitionHolder the bean definition including name and aliases
* @param registry the bean factory to register with
* @throws BeanDefinitionStoreException if registration failed
*/
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 aliase : aliases) {
registry.registerAlias(beanName, aliase);
}
}
}
取到 definitionHolder 的beanname为资源文件bean的id值，definitionHolder.getBeanDefinition()返回对象为 BeanDefinition 类型，其封装了bean定的类的全路径和相应的属性值。
22、进入 registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition())：
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);
}
}
synchronized (this.beanDefinitionMap) {
BeanDefinition oldBeanDefinition = this.beanDefinitionMap.get(beanName);
if (oldBeanDefinition != null) {
if (!this.allowBeanDefinitionOverriding) {
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 (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName +
"': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
}
}
}
else {
this.beanDefinitionNames.add(beanName);
this.frozenBeanDefinitionNames = null;
}
this.beanDefinitionMap.put(beanName, beanDefinition);
}
resetBeanDefinition(beanName);
}
/** List of bean definition names, in registration order */
private final List<String> beanDefinitionNames = new ArrayList<String>();
/** Map of bean definition objects, keyed by bean name */
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(64);
beanDefinitionMap 是存放bean的Map，使用synchronized锁住避免多线程问题，再把 beanDefinitionput 进 beanDefinitionMap中存放起来，bean的id作为key值，可见，spring存放我们通常定义的bean就是使用初始容量为64的ConcurrentHashMap。
23、 看resetBeanDefinition：
/**
* Reset all bean definition caches for the given bean,
* including the caches of beans that are derived from it.
* @param beanName the name of the bean to reset
*/
protected void resetBeanDefinition(String beanName) {
// Remove the merged bean definition for the given bean, if already created.
clearMergedBeanDefinition(beanName);
// Remove corresponding bean from singleton cache, if any. Shouldn't usually
// be necessary, rather just meant for overriding a context's default beans
// (e.g. the default StaticMessageSource in a StaticApplicationContext).
destroySingleton(beanName);
// Remove any assumptions about by-type mappings.
clearByTypeCache();
// Reset all bean definitions that have the given bean as parent (recursively).
for (String bdName : this.beanDefinitionNames) {
if (!beanName.equals(bdName)) {
BeanDefinition bd = this.beanDefinitionMap.get(bdName);
if (beanName.equals(bd.getParentName())) {
resetBeanDefinition(bdName);
}
}
}
}
/**
* Remove the merged bean definition for the specified bean,
* recreating it on next access.
* @param beanName the bean name to clear the merged definition for
*/
protected void clearMergedBeanDefinition(String beanName) {
this.mergedBeanDefinitions.remove(beanName);
}
resetBeanDefinition 方法的参数只有一个，beanName，也就是定义bean的id值，主要是做一些缓存的清理和更新，spring缓存机制篇幅也比较多，至此，就完成了spring资源文件的加载和解析。
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