从xml到document
从document到beanDefinition
从beanDefiniton到instance
涉及到的部分主要类或接口：
org.springframework.beans.factory.xml.BeanDefinitionDocumentReader
org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader
org.springframework.beans.factory.xml.BeanDefinitionParserDelegate
org.springframework.beans.factory.support.BeanDefinitionReaderUtils
org.springframework.beans.factory.config.BeanDefinition
org.springframework.beans.factory.xml.DefaultNamespaceHandlerResolver
从document到beanDefinition
从最直接的xml配置开始
对于像事务tx:annotation等标签在spring-tx.jar/META-INF/spring.handlers下有配置具体的处理类。bean是不是也有一样的配置呢，其实不然，我们找到解析注册标签的入口。
省略从web.xml加载到doc的过程,从解析Element root = doc.getDocumentElement()开始
解析根节点root的任务由DefaultBeanDefinitionDocumentReader开始
DefaultBeanDefinitionDocumentReader源码：
http://www.grepcode.com/file/repository.springsource.com/org.springframework/org.springframework.beans/3.2.2/org/springframework/beans/factory/xml/DefaultBeanDefinitionDocumentReader.java/
DefaultBeanDefinitionDocumentReader.parseBeanDefinitions
/**
* 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)) {
//1.处理默认标签
parseDefaultElement(ele, delegate);
}
else {
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
对于默认的标签，如"import", "alias", "bean" 在parseDefaultElement处开始解析。非默认的标签需定义schema/handlers进行处理。
查看默认标签的处理方法：
DefaultBeanDefinitionDocumentReader#parseDefaultElement
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
//1.1 处理import标签
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
//1.2 处理alias标签
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
//1.3 处理bean标签
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}
继续bean标签的处理BEAN_ELEMENT:
DefaultBeanDefinitionDocumentReader#processBeanDefinition
/**
* Process the given bean element, parsing the bean definition
* and registering it with the registry.
*/
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
//1.3.1 生成beanDefinitionHolder
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
//1.3.2 解析bean标签的自定义元素
//扩展BeanDefinition-自定义标签
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
//1.3.3 注册beanDefinitionMap
// 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));
}
}
从以上代码可以看到,DefaultBeanDefinitionDocumentReader将解析生成beanDefinition的任务委托给了BeanDefinitionParserDelegate进行处理。
beanDefinitionDocumentReader
-------------------------------------------------------承上启下的分割线----------------------------------------------
beanDefinitionParserDelegate
BeanDefinitionParserDelegate源码：
http://grepcode.com/file/repository.springsource.com/org.springframework/org.springframework.beans/3.2.2/org/springframework/beans/factory/xml/BeanDefinitionParserDelegate.java#BeanDefinitionParserDelegate
由上可知,处理bean标签分3个部分：
一是解析bean标签生成BeanDefinitionHolder- 处理spring默认元素或属性
BeanDefinitionParserDelegate#parseBeanDefinitionElement
/**
* Parses the supplied {@code <bean>} element. May return {@code null}
* if there were errors during parse. Errors are reported to the
* {@link org.springframework.beans.factory.parsing.ProblemReporter}.
*/
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
String id = ele.getAttribute(ID_ATTRIBUTE);
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
List aliases = new ArrayList();
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;
}
可以看到，先生成beanDefinition再包装成beanDefinitionHolder
(1)生成beanDefinition的过程
BeanDefinitionParserDelegate#createBeanDefinition
protected AbstractBeanDefinition createBeanDefinition(String className, String parentName)
throws ClassNotFoundException {
return BeanDefinitionReaderUtils.createBeanDefinition(
parentName, className, this.readerContext.getBeanClassLoader());
}
创建GenericBeanDefinition
BeanDefinitionReaderUtils#createBeanDefinition
public static AbstractBeanDefinition createBeanDefinition(
String parentName, String className, ClassLoader classLoader) throws ClassNotFoundException {
GenericBeanDefinition bd = new GenericBeanDefinition();
bd.setParentName(parentName);
if (className != null) {
if (classLoader != null) {
bd.setBeanClass(ClassUtils.forName(className, classLoader));
}
else {
bd.setBeanClassName(className);
}
}
return bd;
}
这里可以发挥你的想象力。就像平时定义了一个model，然后设置各种属性的过程。 这里处理的属性或子标签都是spring默认定义的属性或标签，自定义的标签会在第二步进行处理
bd.setBeanClass涉及到从benDefintion到instance的一个处理过程:resolveBeanClass
如果这里设置了beanClass，resolveBeanClass可以直接返回。
那这里会不会设置beanClass呢？
关键点是this.readerContext.getBeanClassLoader()，其里面继续调用XmlBeanDefinitionReader.getBeanClassLoader();
查看
这里定义的beanDefinition的实际类是GenericBeanDefinition,在从beanDefinition到instance的过程中，会转为RootBeanDefinition
平常我们只会设置几个熟悉的属性，其实beanDefinition中有很多属性,
例如：lookup-method replace-method等
spring是如何解析这些特殊属性或标签的来生成实例的呢？
其他属性可查看BeanDefinitionParserDelegate的源码，其用静态变量基本定义了所有属性
(2)此时生成的beanDefinitionHolder对象也很简单，只是存储了beanDefinition及其名称等
二是装饰第一步生成的BeanDefinitionHolder对象- 处理自定义标签或属性- 可以看做spring的一种扩展-对spring的默认标签进行扩展
public BeanDefinitionHolder decorateBeanDefinitionIfRequired(
Element ele, BeanDefinitionHolder definitionHolder, BeanDefinition containingBd) {
BeanDefinitionHolder finalDefinition = definitionHolder;
// Decorate based on custom attributes first.
NamedNodeMap attributes = ele.getAttributes();
for (int i = 0; i < attributes.getLength(); i++) {
Node node = attributes.item(i);
finalDefinition = decorateIfRequired(node, finalDefinition, containingBd);
}
// Decorate based on custom nested elements.
NodeList children = ele.getChildNodes();
for (int i = 0; i < children.getLength(); i++) {
Node node = children.item(i);
if (node.getNodeType() == Node.ELEMENT_NODE) {
finalDefinition = decorateIfRequired(node, finalDefinition, containingBd);
}
}
return finalDefinition;
}
// Decorate based on custom attributes first.
NamedNodeMap attributes = ele.getAttributes();
// Decorate based on custom nested elements.
NodeList children = ele.getChildNodes();
这里继续循环bean标签的属性或子标签，难道是继续对第一步的属性进行深入处理?其实不然,继续跟到decorateIfRequired方法中看看
private BeanDefinitionHolder decorateIfRequired(
Node node, BeanDefinitionHolder originalDef, BeanDefinition containingBd) {
String namespaceUri = getNamespaceURI(node);
if (!isDefaultNamespace(namespaceUri)) {
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
if (handler != null) {
return handler.decorate(node, originalDef, new ParserContext(this.readerContext, this, containingBd));
}
else if (namespaceUri != null && namespaceUri.startsWith("http://www.springframework.org/")) {
error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", node);
}
else {
// A custom namespace, not to be handled by Spring - maybe "xml:...".
if (logger.isDebugEnabled()) {
logger.debug("No Spring NamespaceHandler found for XML schema namespace [" + namespaceUri + "]");
}
}
}
return originalDef;
}
这段代码中，有个很重要的分子判断!isDefaultNamespace(namespaceUri)，即是否是自定义标签，如果不是则继续获取相应命名空间处理类进行解析
可见装饰主要是对自定义子标签或属性的解析过程- 对spring bean标签的扩展
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
this.readerContext.getNamespaceHandlerResolver()获取的是DefaultNamespaceHandlerResolver，其主要职责是管理命名空间处理器的。其数据来源主要是META-INF/spring.handlers下的内容,加载这些文件用到了懒加载机制(Load the specified NamespaceHandler mappings lazily)
resolve方法中,首先加载META-INF/spring.handler文件:
Properties mappings = PropertiesLoaderUtils.loadAllProperties(this.handlerMappingsLocation, this.classLoader);
并将其Properties类中的文件，转换为hashMap缓存起来:
CollectionUtils.mergePropertiesIntoMap(mappings, handlerMappings);
再就是根据命名空间，读取相应命名空间处理器，并初始化返回:
NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);
将namespaceHandler放入handlerMappings中(之前将Properties转换为hashMap，value值只是string类型的)
handlerMappings.put(namespaceUri, namespaceHandler);
可跟踪源代码,借鉴spring是如何读取配置文件的
DefaultNamespaceHandlerResolver源码:
http://grepcode.com/file/repository.springsource.com/org.springframework/org.springframework.beans/3.2.2/org/springframework/beans/factory/xml/DefaultNamespaceHandlerResolver.java/
三是注册到beanDefinition容器
// Register the final decorated instance. 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);
}
}
}
这里registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());实际上就是放到 DefaultListableBeanFactory.beanDefinitionMap中
至此,从document到beanDefinition分析结束