默认标签解析
概述：本节重点详细分析默认标签的解析过程。接上一篇文章讲到parseBeanDefinitions(root, 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.getNamespaceURI())) {
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;
String namespaceUri = ele.getNamespaceURI();
if (delegate.isDefaultNamespace(namespaceUri)) {
parseDefaultElement(ele, delegate);
}
else {
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}在Spring的XMl配置里面有两个Bean声明，一个是默认的<bean id="test" class="">，一个是<tx:annotation-driven>，两种方式的解析差异非常大。本节讨论默认解析。。。（parseDefaultElement(ele, delegate）。。。
默认标签的解析在函数parseDefaultElement(ele, delegate)中进行，分别对4种不同的标签（import,alias,bean和beans）做了不同处理。源代码如下：
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);
}
}
/**
* 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));
}
}一、首先委托BeanDefinitionDelegate类的parseBeanDefinitionElement方法进行元素的解析，返回BeanDefinitionHolder类型的实例bdHolder，经过这个方法后bdHolder实例已经包含了我们配置文件中的各种属性了，例如class，name，id，alias等。
/**
* 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) {
return parseBeanDefinitionElement(ele, null);
}
/**
* 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;
}
分4步完成：
--提取元素中的id和name属性
--步解析其他所有属性并统一封装到GenericBeanDefinition类型的实例中
/**
* Parse the bean definition itself, without regard to name or aliases. May return
* {@code null} if problems occurred during the parsing of the bean definition.
*/
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
String className = null;
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
try {
String parent = null;
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
parseMetaElements(ele, bd);
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
parseConstructorArgElements(ele, bd);
parsePropertyElements(ele, bd);
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;
}
至此，class属性、parent属性，解析元素，解析lookup-method属性，解析replace-method属性，解析构造函数的参数，解析properties子元素，解析qualifier子元素等已经看到了，下面就是一些复杂标签的解析了。
其中，创建用于属性承载的BeanDefinition
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
BeanDefinition是一个接口，在spring中此接口有三种实现：RootBeanDefinition、ChildBeanDefinition已经GenericBeanDefinition。而三种实现都继承了AbstractBeanDefinition，其中BeanDefinition是配置文件元素标签在容器中的内部表示形式。元素标签拥有class、scope、lazy-init等属性，BeanDefinition则提供了相应的beanClass、scope、lazyInit属性，BeanDefinition和中的属性一一对应。
其中RootBeanDefinition是最常用的实现类，他对应一般性的元素标签，
GenericBeanDefinition是自2.5版本以后新加入的bean文件配置属性定义类，是一站式服务的。
在配置文件中可以定义父和子，父用RootBeanDefinition表示，而子用ChildBeanDefinition表示，而没有父的就使用RootBeanDefinition表示。AbstractBeanDefinition对两者共同的类信息进行抽象。Spring通过BeanDefinition将配置文件中的配置信息转换为容器的内部表示，并将这些BeanDefinition注册到BeanDefinitionRegistry中。Spring容器的BeanDefinitionRegistry就像是Spring配置信息的内存数据库，主要是以map的形式保存，后续操作直接从BeanDefinitionResistry中读取配置信息。代码如下：
/**
* Create a bean definition for the given class name and parent name.
* @param className the name of the bean class
* @param parentName the name of the bean's parent bean
* @return the newly created bean definition
* @throws ClassNotFoundException if bean class resolution was attempted but failed
*/
protected AbstractBeanDefinition createBeanDefinition(String className, String parentName)
throws ClassNotFoundException {
return BeanDefinitionReaderUtils.createBeanDefinition(
parentName, className, this.readerContext.getBeanClassLoader());
}
/**
* Create a new GenericBeanDefinition for the given parent name and class name,
* eagerly loading the bean class if a ClassLoader has been specified.
* @param parentName the name of the parent bean, if any
* @param className the name of the bean class, if any
* @param classLoader the ClassLoader to use for loading bean classes
* (can be {@code null} to just register bean classes by name)
* @return the bean definition
* @throws ClassNotFoundException if the bean class could not be loaded
*/
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;
}
--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。
--将获取到的信息封装到BeanDefinitionHolder的实例中。
（2）当返回的dbHolder不为空的情况下若存在默认标签的子节点下再有自定义属性，还需要再次对自定义标签进行解析。
（3）当解析完成后，需要对解析后的bdHolder进行注册，注册过程委托给了BeanDefinitionReaderUtils的registerBeanDefinition方法。
（4）最后发出响应事件，通知相关的监听器已经加载完这个Bean了。
下面分析解析各种属性：当创建好了承载bean信息的实例后，接下来就是解析各种属性了，首先我们看下parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);方法，代码如下：
/**
* Apply the attributes of the given bean element to the given bean * definition.
* @param ele bean declaration element
* @param beanName bean name
* @param containingBean containing bean definition
* @return a bean definition initialized according to the bean element attributes
*/
public AbstractBeanDefinition parseBeanDefinitionAttributes(Element ele, String beanName,
BeanDefinition containingBean, AbstractBeanDefinition bd) {
if (ele.hasAttribute(SINGLETON_ATTRIBUTE)) {
error("Old 1.x 'singleton' attribute in use - upgrade to 'scope' declaration", ele);
}
else if (ele.hasAttribute(SCOPE_ATTRIBUTE)) {
bd.setScope(ele.getAttribute(SCOPE_ATTRIBUTE));
}
else if (containingBean != null) {
// Take default from containing bean in case of an inner bean definition.
bd.setScope(containingBean.getScope());
}
if (ele.hasAttribute(ABSTRACT_ATTRIBUTE)) {
bd.setAbstract(TRUE_VALUE.equals(ele.getAttribute(ABSTRACT_ATTRIBUTE)));
}
String lazyInit = ele.getAttribute(LAZY_INIT_ATTRIBUTE);
if (DEFAULT_VALUE.equals(lazyInit)) {
lazyInit = this.defaults.getLazyInit();
}
bd.setLazyInit(TRUE_VALUE.equals(lazyInit));
String autowire = ele.getAttribute(AUTOWIRE_ATTRIBUTE);
bd.setAutowireMode(getAutowireMode(autowire));
String dependencyCheck = ele.getAttribute(DEPENDENCY_CHECK_ATTRIBUTE);
bd.setDependencyCheck(getDependencyCheck(dependencyCheck));
if (ele.hasAttribute(DEPENDS_ON_ATTRIBUTE)) {
String dependsOn = ele.getAttribute(DEPENDS_ON_ATTRIBUTE);
bd.setDependsOn(StringUtils.tokenizeToStringArray(dependsOn, MULTI_VALUE_ATTRIBUTE_DELIMITERS));
}
String autowireCandidate = ele.getAttribute(AUTOWIRE_CANDIDATE_ATTRIBUTE);
if ("".equals(autowireCandidate) || DEFAULT_VALUE.equals(autowireCandidate)) {
String candidatePattern = this.defaults.getAutowireCandidates();
if (candidatePattern != null) {
String[] patterns = StringUtils.commaDelimitedListToStringArray(candidatePattern);
bd.setAutowireCandidate(PatternMatchUtils.simpleMatch(patterns, beanName));
}
}
else {
bd.setAutowireCandidate(TRUE_VALUE.equals(autowireCandidate));
}
if (ele.hasAttribute(PRIMARY_ATTRIBUTE)) {
bd.setPrimary(TRUE_VALUE.equals(ele.getAttribute(PRIMARY_ATTRIBUTE)));
}
if (ele.hasAttribute(INIT_METHOD_ATTRIBUTE)) {
String initMethodName = ele.getAttribute(INIT_METHOD_ATTRIBUTE);
if (!"".equals(initMethodName)) {
bd.setInitMethodName(initMethodName);
}
}
else {
if (this.defaults.getInitMethod() != null) {
bd.setInitMethodName(this.defaults.getInitMethod());
bd.setEnforceInitMethod(false);
}
}
if (ele.hasAttribute(DESTROY_METHOD_ATTRIBUTE)) {
String destroyMethodName = ele.getAttribute(DESTROY_METHOD_ATTRIBUTE);
if (!"".equals(destroyMethodName)) {
bd.setDestroyMethodName(destroyMethodName);
}
}
else {
if (this.defaults.getDestroyMethod() != null) {
bd.setDestroyMethodName(this.defaults.getDestroyMethod());
bd.setEnforceDestroyMethod(false);
}
}
if (ele.hasAttribute(FACTORY_METHOD_ATTRIBUTE)) {
bd.setFactoryMethodName(ele.getAttribute(FACTORY_METHOD_ATTRIBUTE));
}
if (ele.hasAttribute(FACTORY_BEAN_ATTRIBUTE)) {
bd.setFactoryBeanName(ele.getAttribute(FACTORY_BEAN_ATTRIBUTE));
}
return bd;
}
可以看到Spring完成了对所有bean属性的解析，包括：解析singleton属性、解析scope属性、解析abstract属性、解析lazy_init属性、解析autowire属性、解析dependsOn属性、解析autowireCandidate属性、解析primary属性、解析init_method属性、解析destroy_method属性、解析factory_method属性、析factory_bean属性。
解析子元素meta属性（parseMetaElements(ele, bd);）
public void parseMetaElements(Element ele, BeanMetadataAttributeAccessor attributeAccessor) {
NodeList nl = ele.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (isCandidateElement(node) && nodeNameEquals(node, META_ELEMENT)) {
Element metaElement = (Element) node;
String key = metaElement.getAttribute(KEY_ATTRIBUTE);
String value = metaElement.getAttribute(VALUE_ATTRIBUTE);
BeanMetadataAttribute attribute = new BeanMetadataAttribute(key, value);
attribute.setSource(extractSource(metaElement));
attributeAccessor.addMetadataAttribute(attribute);
}
}
}解析子元素lookup-method(),(parseLookupOverrideSubElements(ele, bd.getMethodOverrides());)
/**
* Parse lookup-override sub-elements of the given bean element.
*/
public void parseLookupOverrideSubElements(Element beanEle, MethodOverrides overrides) {
NodeList nl = beanEle.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (isCandidateElement(node) && nodeNameEquals(node, LOOKUP_METHOD_ELEMENT)) {
Element ele = (Element) node;
String methodName = ele.getAttribute(NAME_ATTRIBUTE);
String beanRef = ele.getAttribute(BEAN_ELEMENT);
LookupOverride override = new LookupOverride(methodName, beanRef);
override.setSource(extractSource(ele));
overrides.addOverride(override);
}
}
}
解析子元素replaced-method,(parseReplacedMethodSubElements(ele, bd.getMethodOverrides());)
/**
* Parse replaced-method sub-elements of the given bean element.
*/
public void parseReplacedMethodSubElements(Element beanEle, MethodOverrides overrides) {
NodeList nl = beanEle.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (isCandidateElement(node) && nodeNameEquals(node, REPLACED_METHOD_ELEMENT)) {
Element replacedMethodEle = (Element) node;
String name = replacedMethodEle.getAttribute(NAME_ATTRIBUTE);
String callback = replacedMethodEle.getAttribute(REPLACER_ATTRIBUTE);
ReplaceOverride replaceOverride = new ReplaceOverride(name, callback);
// Look for arg-type match elements.
List<Element> argTypeEles = DomUtils.getChildElementsByTagName(replacedMethodEle, ARG_TYPE_ELEMENT);
for (Element argTypeEle : argTypeEles) {
String match = argTypeEle.getAttribute(ARG_TYPE_MATCH_ATTRIBUTE);
match = (StringUtils.hasText(match) ? match : DomUtils.getTextValue(argTypeEle));
if (StringUtils.hasText(match)) {
replaceOverride.addTypeIdentifier(match);
}
}
replaceOverride.setSource(extractSource(replacedMethodEle));
overrides.addOverride(replaceOverride);
}
}
}解析子元素constructor-arg,(parseConstructorArgElements(ele, bd);)
/**
* Parse constructor-arg sub-elements of the given bean element.
*/
public void parseConstructorArgElements(Element beanEle, BeanDefinition bd) {
NodeList nl = beanEle.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (isCandidateElement(node) && nodeNameEquals(node, CONSTRUCTOR_ARG_ELEMENT)) {
parseConstructorArgElement((Element) node, bd);
}
}
}
/**
* Parse a constructor-arg element.
*/
public void parseConstructorArgElement(Element ele, BeanDefinition bd) {
String indexAttr = ele.getAttribute(INDEX_ATTRIBUTE);
String typeAttr = ele.getAttribute(TYPE_ATTRIBUTE);
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
if (StringUtils.hasLength(indexAttr)) {
try {
int index = Integer.parseInt(indexAttr);
if (index < 0) {
error("'index' cannot be lower than 0", ele);
}
else {
try {
this.parseState.push(new ConstructorArgumentEntry(index));
Object value = parsePropertyValue(ele, bd, null);
ConstructorArgumentValues.ValueHolder valueHolder = new ConstructorArgumentValues.ValueHolder(value);
if (StringUtils.hasLength(typeAttr)) {
valueHolder.setType(typeAttr);
}
if (StringUtils.hasLength(nameAttr)) {
valueHolder.setName(nameAttr);
}
valueHolder.setSource(extractSource(ele));
if (bd.getConstructorArgumentValues().hasIndexedArgumentValue(index)) {
error("Ambiguous constructor-arg entries for index " + index, ele);
}
else {
bd.getConstructorArgumentValues().addIndexedArgumentValue(index, valueHolder);
}
}
finally {
this.parseState.pop();
}
}
}
catch (NumberFormatException ex) {
error("Attribute 'index' of tag 'constructor-arg' must be an integer", ele);
}
}
else {
try {
this.parseState.push(new ConstructorArgumentEntry());
Object value = parsePropertyValue(ele, bd, null);
ConstructorArgumentValues.ValueHolder valueHolder = new ConstructorArgumentValues.ValueHolder(value);
if (StringUtils.hasLength(typeAttr)) {
valueHolder.setType(typeAttr);
}
if (StringUtils.hasLength(nameAttr)) {
valueHolder.setName(nameAttr);
}
valueHolder.setSource(extractSource(ele));
bd.getConstructorArgumentValues().addGenericArgumentValue(valueHolder);
}
finally {
this.parseState.pop();
}
}
}
上述代码的流程可以简单的总结为如下：
（1）首先提取index、type、name等属性
（2）根据是否配置了index属性解析流程不同
如果配置了index属性，解析流程如下：
（1）使用parsePropertyValue(ele, bd, null)方法读取constructor-arg的子元素
（2）使用ConstructorArgumentValues.ValueHolder封装解析出来的元素
（3）将index、type、name属性也封装进ValueHolder中，然后将ValueHoder添加到当前beanDefinition的ConstructorArgumentValues的indexedArgumentValues
调用解析子元素的过程：
/**
* Get the value of a property element. May be a list etc.
* Also used for constructor arguments, "propertyName" being null in this case.
*/
public Object parsePropertyValue(Element ele, BeanDefinition bd, String propertyName) {
String elementName = (propertyName != null) ?
"<property> element for property '" + propertyName + "'" :
"<constructor-arg> element";
// Should only have one child element: ref, value, list, etc.
NodeList nl = ele.getChildNodes();
Element subElement = null;
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (node instanceof Element && !nodeNameEquals(node, DESCRIPTION_ELEMENT) &&
!nodeNameEquals(node, META_ELEMENT)) {
// Child element is what we're looking for.
if (subElement != null) {
error(elementName + " must not contain more than one sub-element", ele);
}
else {
subElement = (Element) node;
}
}
}
boolean hasRefAttribute = ele.hasAttribute(REF_ATTRIBUTE);
boolean hasValueAttribute = ele.hasAttribute(VALUE_ATTRIBUTE);
if ((hasRefAttribute && hasValueAttribute) ||
((hasRefAttribute || hasValueAttribute) && subElement != null)) {
error(elementName +
" is only allowed to contain either 'ref' attribute OR 'value' attribute OR sub-element", ele);
}
if (hasRefAttribute) {
String refName = ele.getAttribute(REF_ATTRIBUTE);
if (!StringUtils.hasText(refName)) {
error(elementName + " contains empty 'ref' attribute", ele);
}
RuntimeBeanReference ref = new RuntimeBeanReference(refName);
ref.setSource(extractSource(ele));
return ref;
}
else if (hasValueAttribute) {
TypedStringValue valueHolder = new TypedStringValue(ele.getAttribute(VALUE_ATTRIBUTE));
valueHolder.setSource(extractSource(ele));
return valueHolder;
}
else if (subElement != null) {
return parsePropertySubElement(subElement, bd);
}
else {
// Neither child element nor "ref" or "value" attribute found.
error(elementName + " must specify a ref or value", ele);
return null;
}
}
public Object parsePropertySubElement(Element ele, BeanDefinition bd) {
return parsePropertySubElement(ele, bd, null);
}
上述代码的执行逻辑简单总结为：
（1）首先略过decription和meta属性
（2）提取constructor-arg上的ref和value属性，并验证是否存在
（3）存在ref属性时，用RuntimeBeanReference来封装ref
（4）存在value属性时，用TypedStringValue来封装
（5）存在子元素时，对于子元素的处理使用了方法parsePropertySubElement(subElement, bd);，
代码如下：
/**
* Parse a value, ref or collection sub-element of a property or
* constructor-arg element.
* @param ele subelement of property element; we don't know which yet
* @param defaultValueType the default type (class name) for any
* {@code <value>} tag that might be created
*/
public Object parsePropertySubElement(Element ele, BeanDefinition bd, String defaultValueType) {
if (!isDefaultNamespace(ele)) {
return parseNestedCustomElement(ele, bd);
}
else if (nodeNameEquals(ele, BEAN_ELEMENT)) {
BeanDefinitionHolder nestedBd = parseBeanDefinitionElement(ele, bd);
if (nestedBd != null) {
nestedBd = decorateBeanDefinitionIfRequired(ele, nestedBd, bd);
}
return nestedBd;
}
else if (nodeNameEquals(ele, REF_ELEMENT)) {
// A generic reference to any name of any bean.
String refName = ele.getAttribute(BEAN_REF_ATTRIBUTE);
boolean toParent = false;
if (!StringUtils.hasLength(refName)) {
// A reference to the id of another bean in the same XML file.
refName = ele.getAttribute(LOCAL_REF_ATTRIBUTE);
if (!StringUtils.hasLength(refName)) {
// A reference to the id of another bean in a parent context.
refName = ele.getAttribute(PARENT_REF_ATTRIBUTE);
toParent = true;
if (!StringUtils.hasLength(refName)) {
error("'bean', 'local' or 'parent' is required for <ref> element", ele);
return null;
}
}
}
if (!StringUtils.hasText(refName)) {
error("<ref> element contains empty target attribute", ele);
return null;
}
RuntimeBeanReference ref = new RuntimeBeanReference(refName, toParent);
ref.setSource(extractSource(ele));
return ref;
}
else if (nodeNameEquals(ele, IDREF_ELEMENT)) {
return parseIdRefElement(ele);
}
else if (nodeNameEquals(ele, VALUE_ELEMENT)) {
return parseValueElement(ele, defaultValueType);
}
else if (nodeNameEquals(ele, NULL_ELEMENT)) {
// It's a distinguished null value. Let's wrap it in a TypedStringValue
// object in order to preserve the source location.
TypedStringValue nullHolder = new TypedStringValue(null);
nullHolder.setSource(extractSource(ele));
return nullHolder;
}
else if (nodeNameEquals(ele, ARRAY_ELEMENT)) {
return parseArrayElement(ele, bd);
}
else if (nodeNameEquals(ele, LIST_ELEMENT)) {
return parseListElement(ele, bd);
}
else if (nodeNameEquals(ele, SET_ELEMENT)) {
return parseSetElement(ele, bd);
}
else if (nodeNameEquals(ele, MAP_ELEMENT)) {
return parseMapElement(ele, bd);
}
else if (nodeNameEquals(ele, PROPS_ELEMENT)) {
return parsePropsElement(ele);
}
else {
error("Unknown property sub-element: [" + ele.getNodeName() + "]", ele);
return null;
}
}解析子元素Property,(parsePropertyElements(ele, bd);)
/**
* Parse property sub-elements of the given bean element.
*/
public void parsePropertyElements(Element beanEle, BeanDefinition bd) {
NodeList nl = beanEle.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (isCandidateElement(node) && nodeNameEquals(node, PROPERTY_ELEMENT)) {
parsePropertyElement((Element) node, bd);
}
}
}
解析子元素qualifier,(parseQualifierElements(ele, bd);)
/**
* Parse qualifier sub-elements of the given bean element.
*/
public void parseQualifierElements(Element beanEle, AbstractBeanDefinition bd) {
NodeList nl = beanEle.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (isCandidateElement(node) && nodeNameEquals(node, QUALIFIER_ELEMENT)) {
parseQualifierElement((Element) node, bd);
}
}
}
至此，我们已经完成了从xml配置文件到BeanDefinition的转换，转换后的实例是GenericBeanDefinition的实例。而GenericBeanDefinition是AbstractBeanDefinition的子类，那现在我们就先看下AbstractBeanDefinition中的属性
/**
* Base class for concrete, full-fledged
* {@link org.springframework.beans.factory.config.BeanDefinition} classes,
* factoring out common properties of {@link GenericBeanDefinition},
* {@link RootBeanDefinition} and {@link ChildBeanDefinition}.
*
* <p>The autowire constants match the ones defined in the
* {@link org.springframework.beans.factory.config.AutowireCapableBeanFactory}
* interface.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @author Rob Harrop
* @author Mark Fisher
* @see RootBeanDefinition
* @see ChildBeanDefinition
*/
@SuppressWarnings("serial")
public abstract class AbstractBeanDefinition extends BeanMetadataAttributeAccessor
implements BeanDefinition, Cloneable {
/**
* Constant for the default scope name: "", equivalent to singleton status
* but to be overridden from a parent bean definition (if applicable).
*/
public static final String SCOPE_DEFAULT = "";
/**
* Constant that indicates no autowiring at all.
* @see #setAutowireMode
*/
public static final int AUTOWIRE_NO = AutowireCapableBeanFactory.AUTOWIRE_NO;
/**
* Constant that indicates autowiring bean properties by name.
* @see #setAutowireMode
*/
public static final int AUTOWIRE_BY_NAME = AutowireCapableBeanFactory.AUTOWIRE_BY_NAME;
/**
* Constant that indicates autowiring bean properties by type.
* @see #setAutowireMode
*/
public static final int AUTOWIRE_BY_TYPE = AutowireCapableBeanFactory.AUTOWIRE_BY_TYPE;
/**
* Constant that indicates autowiring a constructor.
* @see #setAutowireMode
*/
public static final int AUTOWIRE_CONSTRUCTOR = AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR;
/**
* Constant that indicates determining an appropriate autowire strategy
* through introspection of the bean class.
* @see #setAutowireMode
* @deprecated as of Spring 3.0: If you are using mixed autowiring strategies,
* use annotation-based autowiring for clearer demarcation of autowiring needs.
*/
@Deprecated
public static final int AUTOWIRE_AUTODETECT = AutowireCapableBeanFactory.AUTOWIRE_AUTODETECT;
/**
* Constant that indicates no dependency check at all.
* @see #setDependencyCheck
*/
public static final int DEPENDENCY_CHECK_NONE = 0;
/**
* Constant that indicates dependency checking for object references.
* @see #setDependencyCheck
*/
public static final int DEPENDENCY_CHECK_OBJECTS = 1;
/**
* Constant that indicates dependency checking for "simple" properties.
* @see #setDependencyCheck
* @see org.springframework.beans.BeanUtils#isSimpleProperty
*/
public static final int DEPENDENCY_CHECK_SIMPLE = 2;
/**
* Constant that indicates dependency checking for all properties
* (object references as well as "simple" properties).
* @see #setDependencyCheck
*/
public static final int DEPENDENCY_CHECK_ALL = 3;
/**
* Constant that indicates the container should attempt to infer the
* {@link #setDestroyMethodName destroy method name} for a bean as opposed to
* explicit specification of a method name. The value {@value} is specifically
* designed to include characters otherwise illegal in a method name, ensuring
* no possibility of collisions with legitimately named methods having the same
* name.
* <p>Currently, the method names detected during destroy method inference
* are "close" and "shutdown", if present on the specific bean class.
*/
public static final String INFER_METHOD = "(inferred)";
private volatile Object beanClass;
private String scope = SCOPE_DEFAULT;
private boolean abstractFlag = false;
private boolean lazyInit = false;
private int autowireMode = AUTOWIRE_NO;
private int dependencyCheck = DEPENDENCY_CHECK_NONE;
private String[] dependsOn;
private boolean autowireCandidate = true;
private boolean primary = false;
private final Map<String, AutowireCandidateQualifier> qualifiers =
new LinkedHashMap<String, AutowireCandidateQualifier>(0);
private boolean nonPublicAccessAllowed = true;
private boolean lenientConstructorResolution = true;
private ConstructorArgumentValues constructorArgumentValues;
private MutablePropertyValues propertyValues;
private MethodOverrides methodOverrides = new MethodOverrides();
private String factoryBeanName;
private String factoryMethodName;
private String initMethodName;
private String destroyMethodName;
private boolean enforceInitMethod = true;
private boolean enforceDestroyMethod = true;
private boolean synthetic = false;
private int role = BeanDefinition.ROLE_APPLICATION;
private String description;
private Resource resource;
/**
* Create a new AbstractBeanDefinition with default settings.
*/
protected AbstractBeanDefinition() {
this(null, null);
}再说一下解析默认标签中的自定义标签元素。
至此，我们已经完成了分析默认标签的解析与提取的过程，回顾一下起始函数。我们已经用了很多篇幅描述BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);接下来我们进行BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);代码的分析，作用就是对BeanDefinition进行装饰。
/**
* 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));
}
}
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
public BeanDefinitionHolder decorateBeanDefinitionIfRequired(Element ele, BeanDefinitionHolder definitionHolder) {
return decorateBeanDefinitionIfRequired(ele, definitionHolder, null);
}
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;
}
上述代码，分别对所有元素的属性以及子节点进行了decorateIfRequired函数的调用。
public 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;
}
程序走到这里已经很清楚了，首先获得元素的属性或者命名空间，以确定该元素或者属性是否适合于自定义标签的解析条件，找出自定义类型所对应的NamespaceHandler并进行进一步解析。
最后就是注册解析。
对于配置文件解析和装饰都完成了，唯一还剩下一步就是processBeanDefinition函数中、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.
使用beanName做唯一的标识
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);
}
}
}从上面的代码可以看出，解析的beanDefinition被注册到BeanDefinitionRegistry类型的实例registry中，而对于beanDefinition的注册分成了两部分：通过beanName的注册和通过别名的注册。
1.通过beanName的注册、registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
//---------------------------------------------------------------------
// Implementation of BeanDefinitionRegistry interface
//---------------------------------------------------------------------
@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 {
注册前的最后一次校验，这里的校验不同于之前的XML的校验
主要是针对AbstractBeanDefinition属性中的methodOverrides校验
校验methodOverrides是否与工厂方法并存或者methodOverrides对应的方法根本不存在。
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
BeanDefinition oldBeanDefinition;
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 {
beanName的记录
this.beanDefinitionNames.add(beanName);
this.manualSingletonNames.remove(beanName);
this.frozenBeanDefinitionNames = null;
}
beanDefinition的注册
this.beanDefinitionMap.put(beanName, beanDefinition);
if (oldBeanDefinition != null || containsSingleton(beanName)) {
重置所有的beanName缓存
resetBeanDefinition(beanName);
}
}综上分析上面代码我们简单总结下对于beanDefinition的注册的处理步骤：
（1）对AbstractBeanDefinition的校验，在解析XML文件的时候我们提过校验，但是此校验非彼校验，之前的校验是针对于XML格式的校验，而此时的校验是针对AbstractBeanDefinition的methodOverrides属性的。
（2）对beanName已经注册的情况的处理，如果设置了不允许bean的覆盖，则需要抛出异常，否陈直接覆盖
（3）加入map缓存
（4）清除解析之前留下的对应beanName的缓存
2.通过别名注册BeanDefinition、registry.registerAlias(beanName, aliase);}
@Override
public void registerAlias(String name, String alias) {
Assert.hasText(name, "'name' must not be empty");
Assert.hasText(alias, "'alias' must not be empty");
//如果beanName与alias相同的，不记录alias，并删除对应的alias
if (alias.equals(name)) {
this.aliasMap.remove(alias);
}
else {
//如果alias不允许被覆盖则抛出异常
if (!allowAliasOverriding()) {
String registeredName = this.aliasMap.get(alias);
if (registeredName != null && !registeredName.equals(name)) {
throw new IllegalStateException("Cannot register alias '" + alias + "' for name '" +
name + "': It is already registered for name '" + registeredName + "'.");
}
}
//核查循环异常
checkForAliasCircle(name, alias);
this.aliasMap.put(alias, name);
}综上述代码的流程总结如下：
（1）alias与beanName相同情况处理，
（2）alias覆盖处理。
（3）alias循环检查，
最终，通知监听器解析及注册工作已完成、getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));这里的实现只为了扩展，当开发人员需要对注册的BeanDefinition事件进行监听的方式并将处理逻辑写入监听器中。
二、alias标签的解析
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}/**
* Process the given alias element, registering the alias with the registry.
*/
protected void processAliasRegistration(Element ele) {
//beanName获取
String name = ele.getAttribute(NAME_ATTRIBUTE);
//alias获取
String alias = ele.getAttribute(ALIAS_ATTRIBUTE);
boolean valid = true;
if (!StringUtils.hasText(name)) {
getReaderContext().error("Name must not be empty", ele);
valid = false;
}
if (!StringUtils.hasText(alias)) {
getReaderContext().error("Alias must not be empty", ele);
valid = false;
}
if (valid) {
try {
//注册alias
getReaderContext().getRegistry().registerAlias(name, alias);
}
catch (Exception ex) {
getReaderContext().error("Failed to register alias '" + alias +
"' for bean with name '" + name + "'", ele, ex);
}
//注册别名后通知监听器做相应的处理
getReaderContext().fireAliasRegistered(name, alias, extractSource(ele));
}
}三、import标签的解析
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}/**
* Parse an "import" element and load the bean definitions
* from the given resource into the bean factory.
*/
protected void importBeanDefinitionResource(Element ele) {
String location = ele.getAttribute(RESOURCE_ATTRIBUTE);
if (!StringUtils.hasText(location)) {
getReaderContext().error("Resource location must not be empty", ele);
return;
}
// Resolve system properties: e.g. "${user.dir}"
location = getReaderContext().getEnvironment().resolveRequiredPlaceholders(location);
Set<Resource> actualResources = new LinkedHashSet<Resource>(4);
// Discover whether the location is an absolute or relative URI
boolean absoluteLocation = false;
try {
absoluteLocation = ResourcePatternUtils.isUrl(location) || ResourceUtils.toURI(location).isAbsolute();
}
catch (URISyntaxException ex) {
// cannot convert to an URI, considering the location relative
// unless it is the well-known Spring prefix "classpath*:"
}
// Absolute or relative?
if (absoluteLocation) {
try {
int importCount = getReaderContext().getReader().loadBeanDefinitions(location, actualResources);
if (logger.isDebugEnabled()) {
logger.debug("Imported " + importCount + " bean definitions from URL location [" + location + "]");
}
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error(
"Failed to import bean definitions from URL location [" + location + "]", ele, ex);
}
}
else {
// No URL -> considering resource location as relative to the current file.
try {
int importCount;
Resource relativeResource = getReaderContext().getResource().createRelative(location);
if (relativeResource.exists()) {
importCount = getReaderContext().getReader().loadBeanDefinitions(relativeResource);
actualResources.add(relativeResource);
}
else {
String baseLocation = getReaderContext().getResource().getURL().toString();
importCount = getReaderContext().getReader().loadBeanDefinitions(
StringUtils.applyRelativePath(baseLocation, location), actualResources);
}
if (logger.isDebugEnabled()) {
logger.debug("Imported " + importCount + " bean definitions from relative location [" + location + "]");
}
}
catch (IOException ex) {
getReaderContext().error("Failed to resolve current resource location", ele, ex);
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to import bean definitions from relative location [" + location + "]",
ele, ex);
}
}
Resource[] actResArray = actualResources.toArray(new Resource[actualResources.size()]);
getReaderContext().fireImportProcessed(location, actResArray, extractSource(ele));
}方法的主要工作如下：
（1）获取resource属性所表示的路径
（2）解析路径中的系统属性
（3）判断location是绝对路径还是相对路径
（4）如果是绝对路径则递归调用bean的解析过程，进行另一次解析
（5）如果是相对路径则计算出绝对路径进行解析
（6）通知监听器，解析完成
至此，默认标签解析结束。。。