從xml到document
[color=red]從document到beanDefinition[/color]
從beanDefiniton到instance
涉及到的部分主要類或接口：
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
[size=large]從document到beanDefinition[/size]
<bean>的解析
從最直接的xml配置開始<bean>
對於像事務tx:annotation等標籤在spring-tx.jar/META-INF/spring.handlers下有配置具體的處理類。bean是不是也有一樣的配置呢，其實不然，我們找到解析註冊標籤的入口。
省略從web.xml加載到doc的過程,從解析Element root = doc.getDocumentElement()開始
[color=red][size=medium]解析根節點root的任務由DefaultBeanDefinitionDocumentReader開始[/size][/color]
DefaultBeanDefinitionDocumentReader源碼：
[url]http://www.grepcode.com/file/repository.springsource.com/org.springframework/org.springframework.beans/3.2.2/org/springframework/beans/factory/xml/DefaultBeanDefinitionDocumentReader.java/[/url]
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.處理默認標籤
parseDefaultElement(ele, delegate);
}
else {
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}對於默認的標籤，如"import", "alias", "bean" 在parseDefaultElement處開始解析。非默認的標籤需定義schema/handlers進行處理。
查看默認標籤的處理方法：
DefaultBeanDefinitionDocumentReader#parseDefaultElement
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
//1.1 處理import標籤
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
//1.2 處理alias標籤
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
//1.3 處理bean標籤
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}繼續bean標籤的處理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標籤的自定義元素
//擴展BeanDefinition-自定義標籤
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
//1.3.3 註冊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));
}
}[color=red][size=medium]從以上代碼可以看到,DefaultBeanDefinitionDocumentReader將解析生成beanDefinition的任務委託給了BeanDefinitionParserDelegate進行處理。[/size][/color]
beanDefinitionDocumentReader
-------------------------------------------------------承上啓下的分割線----------------------------------------------
beanDefinitionParserDelegate
BeanDefinitionParserDelegate源碼：
[url]http://grepcode.com/file/repository.springsource.com/org.springframework/org.springframework.beans/3.2.2/org/springframework/beans/factory/xml/BeanDefinitionParserDelegate.java#BeanDefinitionParserDelegate[/url]
由上可知,處理bean標籤分3個部分：
一是解析bean標籤生成BeanDefinitionHolder-[color=green]處理spring默認元素或屬性[/color]
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<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;
}可以看到，先生成beanDefinition再包裝成beanDefinitionHolder
(1)生成beanDefinition的過程
BeanDefinitionParserDelegate#createBeanDefinition
protected AbstractBeanDefinition createBeanDefinition(String className, String parentName)
throws ClassNotFoundException {
return BeanDefinitionReaderUtils.createBeanDefinition(
parentName, className, this.readerContext.getBeanClassLoader());
}[b][size=medium]創建GenericBeanDefinition[/size][/b]
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;
}這裏可以發揮你的想象力。就像平時定義了一個model，然後設置各種屬性的過程。[color=red]這裏處理的屬性或子標籤都是spring默認定義的屬性或標籤，自定義的標籤會在第二步進行處理[/color]
bd.setBeanClass涉及到從benDefintion到instance的一個處理過程:resolveBeanClass
如果這裏設置了beanClass，resolveBeanClass可以直接返回。
[color=red][size=medium]那這裏會不會設置beanClass呢？[/size][/color]
關鍵點是this.readerContext.getBeanClassLoader()，其裏面繼續調用XmlBeanDefinitionReader.getBeanClassLoader();
查看<spring源碼學習系列2.1-從xml到document>創建XmlBeanDefinitionReader對象時，並沒有設置beanClassLoader的值
[color=red][size=medium]這裏定義的beanDefinition的實際類是GenericBeanDefinition,在從beanDefinition到instance的過程中，會轉爲RootBeanDefinition[/size][/color]
平常我們只會設置幾個熟悉的屬性，其實beanDefinition中有很多屬性,
例如：lookup-method replace-method等
[color=red]spring是如何解析這些特殊屬性或標籤的來生成實例的呢？[/color]
其他屬性可查看BeanDefinitionParserDelegate的源碼，其用靜態變量基本定義了所有屬性
(2)此時生成的beanDefinitionHolder對象也很簡單，只是存儲了beanDefinition及其名稱等
二是裝飾第一步生成的BeanDefinitionHolder對象-[color=green]處理自定義標籤或屬性[/color]-[color=red][size=medium]可以看做spring的一種擴展[/size][/color]-對spring的默認標籤進行擴展
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();
這裏繼續循環bean標籤的屬性或子標籤，難道是繼續對第一步的屬性進行深入處理?其實不然,繼續跟到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;
}這段代碼中，有個很重要的分子判斷!isDefaultNamespace(namespaceUri)，即是否是自定義標籤，如果不是則繼續獲取相應命名空間處理類進行解析
可見裝飾主要是對自定義子標籤或屬性的解析過程-[color=red][size=medium]對spring bean標籤的擴展[/size][/color]
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);this.readerContext.getNamespaceHandlerResolver()獲取的是DefaultNamespaceHandlerResolver，其主要職責是管理命名空間處理器的。其數據來源主要是META-INF/spring.handlers下的內容,加載這些文件用到了懶加載機制(Load the specified NamespaceHandler mappings lazily)
resolve方法中,首先加載META-INF/spring.handler文件:
Properties mappings =
PropertiesLoaderUtils.loadAllProperties(this.handlerMappingsLocation, this.classLoader);並將其Properties類中的文件，轉換爲hashMap緩存起來:
CollectionUtils.mergePropertiesIntoMap(mappings, handlerMappings);再就是根據命名空間，讀取相應命名空間處理器，並初始化返回:
NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);將namespaceHandler放入handlerMappings中(之前將Properties轉換爲hashMap，value值只是string類型的)
handlerMappings.put(namespaceUri, namespaceHandler);[color=red]可跟蹤源代碼,借鑑spring是如何讀取配置文件的[/color]
DefaultNamespaceHandlerResolver源碼:
[url]http://grepcode.com/file/repository.springsource.com/org.springframework/org.springframework.beans/3.2.2/org/springframework/beans/factory/xml/DefaultNamespaceHandlerResolver.java/[/url]
三是註冊到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);
}
}
}這裏registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());實際上就是放到[b][size=medium]DefaultListableBeanFactory.beanDefinitionMap[/size][/b]中
至此,從document到beanDefinition分析結束