Spring初始化loadBeanDefinition过程中，根据xml配置和注解的方式分别使用XmlBeanDefinitionReader和AnnotatedBeanDefinitionReader两种方式现在主要了解XmlBeanDefinitionReader；解析流程图如下：
首先看看doLoadBeanDefinitions()方法：
/**
* 加载resource资源，解析并注册BeanDefinition
* Actually load bean definitions from the specified XML file.
* @param inputSource the SAX InputSource to read from
* @param resource the resource descriptor for the XML file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
* @see #doLoadDocument
* @see #registerBeanDefinitions
*/
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
//解析resource，创建doc文档
Document doc = doLoadDocument(inputSource, resource);
//注册BeanDefinition
return registerBeanDefinitions(doc, resource);
}
//.........................
}
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
documentReader.setEnvironment(this.getEnvironment());
//用于统计BeanDefinition的数量
int countBefore = getRegistry().getBeanDefinitionCount();
//DefaultBeanDefinitionDocumentReader注册BeanDefinition
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}DefaultBeanDefinitionDocumentReader：解析doc，并注册
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
//拿到doc根元素
Element root = doc.getDocumentElement();
//解析注册
doRegisterBeanDefinitions(root);
}
/**
* 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);
//解析注册
parseBeanDefinitions(root, this.delegate);
postProcessXml(root);
this.delegate = parent;
}
/**
* 解析xml
* 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;
//spring提供的默认节点
if (delegate.isDefaultNamespace(ele)) {
parseDefaultElement(ele, delegate);
}
else {
//解析自定义Schema节点
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
//解析import元素节点
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
//解析alias元素节点
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
//解析bean元素节点
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}
/**
* 解析bean元素节点，并将生成的BeanDefinition注册到BeanDefinitionRegistry中
* Process the given bean element, parsing the bean definition
* and registering it with the registry.
*/
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
//BeanDefinition持有器
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
//解析当前节点的属性、子节点等
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
//注册BeanDefinition到DefaultListableBeanFactory中
// 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));
}
}
//BeanDefinitionReaderUtils：
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
// Register bean definition under primary name.
String beanName = definitionHolder.getBeanName();
//bean===>注册到beanFactory中
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// Register aliases for bean name, if any.
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String aliase : aliases) {
//Alias===>b
registry.registerAlias(beanName, aliase);
}
}
}
//DefaultListableBeanFactory:
@Override
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) {
//...........
}
else {
this.beanDefinitionNames.add(beanName);
this.frozenBeanDefinitionNames = null;
}
//添加beanDefinition
this.beanDefinitionMap.put(beanName, beanDefinition);
}
//重置==》Reset all bean definition caches for the given bean
resetBeanDefinition(beanName);
}来源：oschina
链接：https://my.oschina.net/u/1263326/blog/534274