概述
在上一篇文章中讲到Spring通过实现接口BeanDefinitionDocumentReader的DefaultBeanDefinitionDocumentReader类对Document进行解析,并使用BeanDefinitionParserDelegate对Element进行解析。
Spring的默认标签主要分为4中不同的标签(import、alias、bean和beans)
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
//对import标签处理
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
//对alias标签处理
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
// 对bean标签处理
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
// beans标签处理
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}
默认标签Bean解析注册
主要分析Bean标签的解析及注册,解析过程主要在BeanDefinitionParserDelegate类中进行
源码
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) {
return parseBeanDefinitionElement(ele, null);
}
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
//(步骤1)
String id = ele.getAttribute(ID_ATTRIBUTE);
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
List<String> aliases = new ArrayList<String>();
//(步骤3)
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);
}
//(步骤2)
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);
// (步骤4)
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
return null;
}
以上为默认标签解析的全过程,在当前层主要完成的工作包括如下内容:
(1)提取元素中的id以及name属性
(2)进一步解析其他所有属性并同意封装值GenericBeanDefinition类型的实例中
(3)如果检测到bean没有指定beanName,那么使用默认规则为此Bean生成beanName
(4)将获取到的信息封装到BeanDefinitionHolder的实例中
步骤(2)中对其他标签属性解析过程
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
String className = null;
// 解析class属性
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
try {
String parent = null;
// 解析parent属性
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
// 用户创建承载属性的AbstractBeanDefinition
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
// 硬编码解析默认bean的各种属性
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
// 提取description
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
// 解析元数据
parseMetaElements(ele, bd);
// 解析lookup-method属性
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
// 解析replaced-method属性
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
// 解析构造函数参数
parseConstructorArgElements(ele, bd);
// 解析property子元素
parsePropertyElements(ele, bd);
// 解析qualifier子元素
parseQualifierElements(ele, bd);
bd.setResource(this.readerContext.getResource());
bd.setSource(extractSource(ele));
return bd;
}
catch (ClassNotFoundException ex) {
error("Bean class [" + className + "] not found", ele, ex);
}
catch (NoClassDefFoundError err) {
error("Class that bean class [" + className + "] depends on not found", ele, err);
}
catch (Throwable ex) {
error("Unexpected failure during bean definition parsing", ele, ex);
}
finally {
this.parseState.pop();
}
return null;
}