parseBeanDefinitions方法
//根据root元素开始进行Bean定义
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
//Spring默认的XML命名空间
if (delegate.isDefaultNamespace(root)) {
//获取根元素的所有子节点
NodeList nl = root.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
//判断是否是元素节点
if (node instanceof Element) {
Element ele = (Element) node;
//Bean定义的Document的元素节点使用的是Spring默认的XML命名空间
if (delegate.isDefaultNamespace(ele)) {
//解析默认的元素
parseDefaultElement(ele, delegate);
}
else {
//解析自定义的元素
delegate.parseCustomElement(ele);
}
}
}
}
else {
//解析自定义的元素
delegate.parseCustomElement(root);
}
}
parseDefaultElement方法
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
//元素节点是<import>元素，进行导入解析
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
//元素节点是<alias>元素，进行导入解析
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
//元素节点是<bean>元素，进行导入解析
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
//元素节点是<beans>元素，进行导入解析
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}
processBeanDefinition方法
/**
* Process the given bean element, parsing the bean definition
* and registering it with the registry.
*/
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
//BeanDefinitionHolder见名知意，BeanDefinition的持有者,封装了BeanDefinition，Bean的名字和别名
//用它来完成IOC容器注册.BeanDefinitionHolder 意味着BeanDefinition是通过BeanDefinitionParserDelegate
//对XML元素的信息按照Spring的Bean规则进行解析得到的
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
//装饰
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
//这里是向IOC容器注册解析得到BeanDefinition的地方，这个在最后说明
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// Send registration event.
//在BeanDefinition向IOC容器注册完成以后，发送注册事件
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
public class BeanDefinitionHolder implements BeanMetadataElement {
private final BeanDefinition beanDefinition;
private final String beanName;
private final String[] aliases;
...
}
下面我们来看一下BeanDefinitionParserDelegate如何解析Bean定义资源文件中的<Bean>元素：
//解析<Bean>元素的入口
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}.
*/
//该方法用于解析<bean>元素的id，name 和aliase属性的值
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
//获取<bean>元素中的id属性值
String id = ele.getAttribute(ID_ATTRIBUTE);
//获取<bean>元素中的name属性值
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
//将<bean>元素中的所有name属性值存放到别名中
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;
//如果<bean>元素中没有配置id属性时，则将别名中的第一个值赋值给beanName
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) {
//检查<bean>元素所配置的id、name(解析成的beanName)或者aliases是否重复
checkNameUniqueness(beanName, aliases, ele);
}
//这个方法是对Bean元素的详细解析
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;
}
/**
* 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) {
//记录解析的<Bean> (放入Stack中)
this.parseState.push(new BeanEntry(beanName));
//获取<bean>元素中的class属性值
String className = null;
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
try {
//获取<bean>元素中的parent属性值
String parent = null;
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
//这里生成需要的BeanDefinition对象，为Bean定义信息的载入做准备
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
//对当前的<bean>元素中配置的一些属性进行解析并设置（包括scope，lazy-init，autowire等）
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
//设置description的信息
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
//对<bean>元素的meta(元信息)属性解析
parseMetaElements(ele, bd);
//对<bean>元素的lookup-method属性解析
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
//对<bean>元素的replaced-method属性解析
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
//对<bean>元素的构造方法设置
parseConstructorArgElements(ele, bd);
//对<bean>元素的property设置，property这个配置比较常见，下面做详细讲解
parsePropertyElements(ele, bd);
//对<bean>元素的qualifier设置
parseQualifierElements(ele, bd);
//为当前解析的Bean设置所需的资源和依赖对象
bd.setResource(this.readerContext.getResource());
bd.setSource(extractSource(ele));
return bd;
}
//<bean>元素配置出问题时抛出的异常
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 {
//移除记录<Bean>
this.parseState.pop();
}
return null;
}
BeanDefinitionParserDelegate如何解析Bean定义资源文件中的<Bean>元素下的<property>属性：
//这里的方法比较简单，我们直接看parsePropertyElement方法
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);
}
}
}
public void parsePropertyElement(Element ele, BeanDefinition bd) {
//获取<property>元素的name属性
String propertyName = ele.getAttribute(NAME_ATTRIBUTE);
if (!StringUtils.hasLength(propertyName)) {
error("Tag 'property' must have a 'name' attribute", ele);
return;
}
this.parseState.push(new PropertyEntry(propertyName));
try {
//如果一个Bean中已经有同名的property存在，则不进行解析，直接返回。也就是说，
//如果在同一个Bean中有同名的property设置，那么起作用的只有第一个
if (bd.getPropertyValues().contains(propertyName)) {
error("Multiple 'property' definitions for property '" + propertyName + "'", ele);
return;
}
//解析获取property的值
Object val = parsePropertyValue(ele, bd, propertyName);
//将结果封装到PropertyValue对象中
PropertyValue pv = new PropertyValue(propertyName, val);
//对<property>元素的meta(元信息)属性解析
parseMetaElements(ele, pv);
pv.setSource(extractSource(ele));
//向MutablePropertyValues对象中添加PropertyValue
bd.getPropertyValues().addPropertyValue(pv);
}
finally {
this.parseState.pop();
}
}
/**
* 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.
//由英文注释我们可以知道这里应该只有一个子元素
NodeList nl = ele.getChildNodes();
Element subElement = null;
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
//子元素不是description和meta属性
if (node instanceof Element && !nodeNameEquals(node, DESCRIPTION_ELEMENT) &&
!nodeNameEquals(node, META_ELEMENT)) {
//这里判断是否只有一个子元素，并赋值
if (subElement != null) {
error(elementName + " must not contain more than one sub-element", ele);
}
else {
subElement = (Element) node;
}
}
}
//解析获取<property>的属性值,是ref还是value，不允许同时事ref和value
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);
}
//ref属性
if (hasRefAttribute) {
//获取<property>元素中的ref属性值
String refName = ele.getAttribute(REF_ATTRIBUTE);
if (!StringUtils.hasText(refName)) {
error(elementName + " contains empty 'ref' attribute", ele);
}
//RuntimeBeanReference里面封装了beanName
RuntimeBeanReference ref = new RuntimeBeanReference(refName);
ref.setSource(extractSource(ele));
return ref;
}
//value属性
else if (hasValueAttribute) {
//TypedStringValue里面封装了配置文件中value的值
TypedStringValue valueHolder = new TypedStringValue(ele.getAttribute(VALUE_ATTRIBUTE));
valueHolder.setSource(extractSource(ele));
return valueHolder;
}
//解析<property>的子元素
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);
}
/**
* 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) {
//不是默认命名空间，通过自定义的解析规则解析
if (!isDefaultNamespace(ele)) {
return parseNestedCustomElement(ele, bd);
}
//子元素是bean
else if (nodeNameEquals(ele, BEAN_ELEMENT)) {
BeanDefinitionHolder nestedBd = parseBeanDefinitionElement(ele, bd);
if (nestedBd != null) {
nestedBd = decorateBeanDefinitionIfRequired(ele, nestedBd, bd);
}
return nestedBd;
}
//子元素是ref
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;
}
//子元素是idref
else if (nodeNameEquals(ele, IDREF_ELEMENT)) {
return parseIdRefElement(ele);
}
//子元素是value
else if (nodeNameEquals(ele, VALUE_ELEMENT)) {
return parseValueElement(ele, defaultValueType);
}
//子元素是null
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;
}
//子元素是array
else if (nodeNameEquals(ele, ARRAY_ELEMENT)) {
return parseArrayElement(ele, bd);
}
//子元素是list
else if (nodeNameEquals(ele, LIST_ELEMENT)) {
return parseListElement(ele, bd);
}
//子元素是set
else if (nodeNameEquals(ele, SET_ELEMENT)) {
return parseSetElement(ele, bd);
}
//子元素是map
else if (nodeNameEquals(ele, MAP_ELEMENT)) {
return parseMapElement(ele, bd);
}
//子元素是props
else if (nodeNameEquals(ele, PROPS_ELEMENT)) {
return parsePropsElement(ele);
}
else {
error("Unknown property sub-element: [" + ele.getNodeName() + "]", ele);
return null;
}
}
BeanDefinitionParserDelegate如何解析Bean定义资源文件中的<Bean>元素下的<property>属性下的<list>：
public Object parseArrayElement(Element arrayEle, BeanDefinition bd) {
//获取<list>元素中的value-type属性，即获取集合元素的数据类型
String elementType = arrayEle.getAttribute(VALUE_TYPE_ATTRIBUTE);
NodeList nl = arrayEle.getChildNodes();
ManagedArray target = new ManagedArray(elementType, nl.getLength());
target.setSource(extractSource(arrayEle));
target.setElementTypeName(elementType);
target.setMergeEnabled(parseMergeAttribute(arrayEle));
//具体的list元素解析过程
parseCollectionElements(nl, target, bd, elementType);
return target;
}
protected void parseCollectionElements(
NodeList elementNodes, Collection<Object> target, BeanDefinition bd, String defaultElementType) {
for (int i = 0; i < elementNodes.getLength(); i++) {
Node node = elementNodes.item(i);
if (node instanceof Element && !nodeNameEquals(node, DESCRIPTION_ELEMENT)) {
//将解析的元素加入集合中，这是一个递归的调用
target.add(parsePropertySubElement((Element) node, bd, defaultElementType));
}
}
}
我们上面做的所有步骤，其实就是为了获得BeanDefinitionHolder 对象，下面我们来看看关键的注册bean定义的方法
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
// Register bean definition under primary name.
//注册bean定义
String beanName = definitionHolder.getBeanName();
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// Register aliases for bean name, if any.
//注册别名
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);
}
}
}
//我们来看下DefaultListableBeanFactory中的实现
@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");
//校验解析beanDefiniton
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
BeanDefinition oldBeanDefinition;
//beanDefinitionMap就是我们在第4章中说到的很关键的一个成员变量
oldBeanDefinition = this.beanDefinitionMap.get(beanName);
//判断是否已经有同名的beanName注册过
//beanName已经注册过
if (oldBeanDefinition != null) {
//是有允许被覆盖，不允许则抛异常
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
"': There is already [" + oldBeanDefinition + "] bound.");
}
//Bean角色 ROLE_APPLICATION = 0;ROLE_SUPPORT = 1;ROLE_INFRASTRUCTURE = 2;
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 + "]");
}
}
//不是同一个BeanDefinition
else if (!beanDefinition.equals(oldBeanDefinition)) {
if (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
//放入线程安全的map中
this.beanDefinitionMap.put(beanName, beanDefinition);
}
//beanName没有被注册过
else {
//bean Name是否至少被创建过一次
if (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
synchronized (this.beanDefinitionMap) {
//放入beanDefinitionMap中
this.beanDefinitionMap.put(beanName, beanDefinition);
//将beanName放入List中
List<String> updatedDefinitions = new ArrayList<String>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
//判断单例模式的bean中是否有该beanName，有就移除。
if (this.manualSingletonNames.contains(beanName)) {
Set<String> updatedSingletons = new LinkedHashSet<String>(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
// Still in startup registration phase
//放入beanDefinitionMap中
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (oldBeanDefinition != null || containsSingleton(beanName)) {
//重置所有已经注册过的BeanDefinition的缓存
resetBeanDefinition(beanName);
}
}
至此,完成了BeanDefinition的注册，也就完成了IOC容器的整个初始化过程。IOC容器中已经建立了整个Bean的配置信息,而且这些BeanDefinition已经可以被容器所使用了，它们都在beanDefinitionMap中被检索和使用。有了这些基础数据，容器就可以完成依赖注入了。下图是IOC容器初始化的时序图:
spring_ioc.jpg
