个人学习Spring源码系列 默认标签的解析
目录
个人学习Spring源码系列 默认标签的解析
默认标签种类
一、Bean标签的解析和注册
(1)解析BeanDefinition
1.创建用于属性承载的BeanDefinition
2.解析各种属性，硬编码解析默认的bean的各种属性
3.解析元数据meta
4.解析子元素lookup-method
5.解析子元素replaced-method
6.解析子元素constructor-arg
7.解析子元素property
8.解析子元素qualifier
(2) AbstractBeanDefinition属性
(3)解析默认标签中自定义标签元素
(4)注册解析的BeanDefinition
1.通过BeanName注册BeanDefinition
2.通过别名注册BeanDefinition
二、alias标签的解析
三、import标签的解析
默认标签种类
Spring中的标签包括默认标签和自定义标签两种，本文主要记录默认标签的解析过程，分别对4种不同标签import, alias, bean 和beans做了不同的处理
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
//对import标签的处理
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
//对alias标签的处理
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
//对bean标签的处理
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
//对beans标签的处理
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}一、Bean标签的解析和注册
(1)解析BeanDefinition
processBeanDefinition()
/**
* 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));
}
}
Bean标签的解析和注册时序图
解析BeanDefinition
首先从元素解析及信息提取开始,BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele); 对Spring的解析犹如洋葱剥皮，一层一层的进行，主要工作包括如下
/**
* 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}.
*/
@Nullable
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}.
*/
@Nullable
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
//解析id属性
String id = ele.getAttribute(ID_ATTRIBUTE);
//解析name属性
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
//分割name属性
List<String> 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.isTraceEnabled()) {
logger.trace("No XML 'id' specified - using '" + beanName +
"' as bean name and " + aliases + " as aliases");
}
}
if (containingBean == null) {
checkNameUniqueness(beanName, aliases, ele);
}
//步骤2中对标签其他属性的解析过程
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
if (!StringUtils.hasText(beanName)) {
try {
//如果不存在beanName根据Spring中提供的命名规则为当前bean生成对应的beanName
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.isTraceEnabled()) {
logger.trace("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;
}第二步具体解析过程
/**
* 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.
*/
@Nullable
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, @Nullable BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
//解析class属性
String className = null;
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
//解析parent属性
String parent = null;
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
//创建用于承载属性的AbstractBeanDefinition类型的GenericBeanDefinition
try {
//1.创建用于属性承载的BeanDefinition
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
//2.解析各种属性，硬编码解析默认的bean的各种属性
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
//3.解析元数据meta
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;
}1.创建用于属性承载的BeanDefinition
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
BeanDefinition是一个接口，在Spring中存在三种实现：RootBeanDefinition，ChildBeanDefinition和GenericBeanDefinition，均继承了AbstractBeanDefinition。BeanDefinition提供了相应的beanClass, scope, lazyInit属性。
/**
* 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(@Nullable String className, @Nullable 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(
@Nullable String parentName, @Nullable String className, @Nullable ClassLoader classLoader) throws ClassNotFoundException {
GenericBeanDefinition bd = new GenericBeanDefinition();
//parentName可能为空
bd.setParentName(parentName);
if (className != null) {
//如果classLoader不为空，则使用以传入的classLoader同一虚拟机加载类对象，否则只是记录className
if (classLoader != null) {
bd.setBeanClass(ClassUtils.forName(className, classLoader));
}
else {
bd.setBeanClassName(className);
}
}
return bd;
}2.解析各种属性，硬编码解析默认的bean的各种属性
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
/**
* 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,
@Nullable BeanDefinition containingBean, AbstractBeanDefinition bd) {
//解析Singleton属性
if (ele.hasAttribute(SINGLETON_ATTRIBUTE)) {
error("Old 1.x 'singleton' attribute in use - upgrade to 'scope' declaration", ele);
}
//解析Scope属性
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());
}
//解析abstract属性
if (ele.hasAttribute(ABSTRACT_ATTRIBUTE)) {
bd.setAbstract(TRUE_VALUE.equals(ele.getAttribute(ABSTRACT_ATTRIBUTE)));
}
//解析lazy-init属性
String lazyInit = ele.getAttribute(LAZY_INIT_ATTRIBUTE);
if (isDefaultValue(lazyInit)) {
lazyInit = this.defaults.getLazyInit();
}
bd.setLazyInit(TRUE_VALUE.equals(lazyInit));
//解析autowire属性
String autowire = ele.getAttribute(AUTOWIRE_ATTRIBUTE);
bd.setAutowireMode(getAutowireMode(autowire));
//解析depends-on属性
if (ele.hasAttribute(DEPENDS_ON_ATTRIBUTE)) {
String dependsOn = ele.getAttribute(DEPENDS_ON_ATTRIBUTE);
bd.setDependsOn(StringUtils.tokenizeToStringArray(dependsOn, MULTI_VALUE_ATTRIBUTE_DELIMITERS));
}
//解析autowire-candidate属性
String autowireCandidate = ele.getAttribute(AUTOWIRE_CANDIDATE_ATTRIBUTE);
if (isDefaultValue(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));
}
//解析primary属性
if (ele.hasAttribute(PRIMARY_ATTRIBUTE)) {
bd.setPrimary(TRUE_VALUE.equals(ele.getAttribute(PRIMARY_ATTRIBUTE)));
}
//解析init-method属性
if (ele.hasAttribute(INIT_METHOD_ATTRIBUTE)) {
String initMethodName = ele.getAttribute(INIT_METHOD_ATTRIBUTE);
bd.setInitMethodName(initMethodName);
}
else if (this.defaults.getInitMethod() != null) {
bd.setInitMethodName(this.defaults.getInitMethod());
bd.setEnforceInitMethod(false);
}
//解析destroy-method属性
if (ele.hasAttribute(DESTROY_METHOD_ATTRIBUTE)) {
String destroyMethodName = ele.getAttribute(DESTROY_METHOD_ATTRIBUTE);
bd.setDestroyMethodName(destroyMethodName);
}
else if (this.defaults.getDestroyMethod() != null) {
bd.setDestroyMethodName(this.defaults.getDestroyMethod());
bd.setEnforceDestroyMethod(false);
}
//解析factory-method属性
if (ele.hasAttribute(FACTORY_METHOD_ATTRIBUTE)) {
bd.setFactoryMethodName(ele.getAttribute(FACTORY_METHOD_ATTRIBUTE));
}
//解析factory-bean属性
if (ele.hasAttribute(FACTORY_BEAN_ATTRIBUTE)) {
bd.setFactoryBeanName(ele.getAttribute(FACTORY_BEAN_ATTRIBUTE));
}
return bd;
}3.解析元数据meta
parseMetaElements(ele, bd);
/**
* Parse the meta elements underneath the given element, if any.
*/
public void parseMetaElements(Element ele, BeanMetadataAttributeAccessor attributeAccessor) {
//获取当前节点的所有子元素
NodeList nl = ele.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
//提取Meta
if (isCandidateElement(node) && nodeNameEquals(node, META_ELEMENT)) {
Element metaElement = (Element) node;
String key = metaElement.getAttribute(KEY_ATTRIBUTE);
String value = metaElement.getAttribute(VALUE_ATTRIBUTE);
//使用Key、Value构造BeanMetadataAttribute
BeanMetadataAttribute attribute = new BeanMetadataAttribute(key, value);
attribute.setSource(extractSource(metaElement));
//记录信息
attributeAccessor.addMetadataAttribute(attribute);
}
}
}4.解析子元素lookup-method
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
配置文件中使用了lookup-method子元素，动态的将teacher所代表的bean作为getBean的返回值，当teacher的业务逻辑已经不再符合我们的业务要求可以进行替换
/**
* 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);
//仅在Spring Bean的子元素下且为lookup-method是有效
if (isCandidateElement(node) && nodeNameEquals(node, LOOKUP_METHOD_ELEMENT)) {
Element ele = (Element) node;
//获取要修饰的方法
String methodName = ele.getAttribute(NAME_ATTRIBUTE);
//获取配置返回的bean
String beanRef = ele.getAttribute(BEAN_ELEMENT);
LookupOverride override = new LookupOverride(methodName, beanRef);
override.setSource(extractSource(ele));
overrides.addOverride(override);
}
}
}5.解析子元素replaced-method
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
方法替换，可以在运行时用新的方法替换现有的方法，replaced-method不仅可以动态的替换返回的实体bean,还能动态的更改原有方法的逻辑
/**
* 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);
//仅在Spring bean子元素写下为replaced-method时有效
if (isCandidateElement(node) && nodeNameEquals(node, REPLACED_METHOD_ELEMENT)) {
Element replacedMethodEle = (Element) node;
//提取要替换的旧的方法
String name = replacedMethodEle.getAttribute(NAME_ATTRIBUTE);
//提取对应新的替换方法
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) {
//记录参数
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);
}
}
}6.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) {
//提取index属性
String indexAttr = ele.getAttribute(INDEX_ATTRIBUTE);
//提取type属性
String typeAttr = ele.getAttribute(TYPE_ATTRIBUTE);
//提取name属性
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));
//解析ele对应的属性
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));
//不允许重复指定相同参数
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 {
//没有index属性则忽略去属性,自动寻找
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();
}
}
}如果配置中指定了index属性
1.解析constructor-arg的子元素
2.使用ConstructorArgumentValues.ValueHolder类型封装解析出来的元素
3.使用type,name和index属性一并封装在ConstructorArgumentValues.ValueHolder并添加至BeanDefinition的addIndexedArgumentValue属性中
如果配置中没有指定index属性
1.解析constructor-arg的子元素
2.使用ConstructorArgumentValues.ValueHolder类型封装解析出来的元素
3.使用type,name和index属性一并封装在ConstructorArgumentValues.ValueHolder并添加至BeanDefinition的addGenericArgumentValue属性中
进一步解析构造函数配置中子元素的过程，进入parsePropertyValue()
/**
* Get the value of a property element. May be a list etc.
* Also used for constructor arguments, "propertyName" being null in this case.
*/
@Nullable
public Object parsePropertyValue(Element ele, BeanDefinition bd, @Nullable String propertyName) {
String elementName = (propertyName != null ?
"<property> element for property '" + propertyName + "'" :
"<constructor-arg> element");
// 一个属性只能对应一种类型：ref、value、list. 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;
}
}
}
//解析ref属性
boolean hasRefAttribute = ele.hasAttribute(REF_ATTRIBUTE);
//解析value属性
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) {
//解析子元素
return parsePropertySubElement(subElement, bd);
}
else {
//既没有ref 也没有value也没有子元素,Neither child element nor "ref" or "value" attribute found.
error(elementName + " must specify a ref or value", ele);
return null;
}
}解析子元素parsePropertySubElement(subElement, bd)
/**
* 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 bd the current bean definition (if any)
*/
@Nullable
public Object parsePropertySubElement(Element ele, @Nullable 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 bd the current bean definition (if any)
* @param defaultValueType the default type (class name) for any
* {@code <value>} tag that might be created
*/
@Nullable
public Object parsePropertySubElement(Element ele, @Nullable BeanDefinition bd, @Nullable 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)) {
//解析local A generic reference to any name of any bean.
String refName = ele.getAttribute(BEAN_REF_ATTRIBUTE);
boolean toParent = false;
if (!StringUtils.hasLength(refName)) {
//解析parent 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' 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);
}
//对value子元素的解析
else if (nodeNameEquals(ele, VALUE_ELEMENT)) {
return parseValueElement(ele, defaultValueType);
}
//对null子元素的解析
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)) {
//解析array子元素
return parseArrayElement(ele, bd);
}
else if (nodeNameEquals(ele, LIST_ELEMENT)) {
//解析list子元素
return parseListElement(ele, bd);
}
else if (nodeNameEquals(ele, SET_ELEMENT)) {
//解析set子元素
return parseSetElement(ele, bd);
}
else if (nodeNameEquals(ele, MAP_ELEMENT)) {
//解析map子元素
return parseMapElement(ele, bd);
}
else if (nodeNameEquals(ele, PROPS_ELEMENT)) {
//解析props子元素
return parsePropsElement(ele);
}
else {
error("Unknown property sub-element: [" + ele.getNodeName() + "]", ele);
return null;
}
}7.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);
}
}
}
/**
* Parse a property element.
*/
public void parsePropertyElement(Element ele, BeanDefinition bd) {
//获取配置元素中name的值
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 {
//不允许多次对同一属性配置
if (bd.getPropertyValues().contains(propertyName)) {
error("Multiple 'property' definitions for property '" + propertyName + "'", ele);
return;
}
Object val = parsePropertyValue(ele, bd, propertyName);
PropertyValue pv = new PropertyValue(propertyName, val);
parseMetaElements(ele, pv);
pv.setSource(extractSource(ele));
bd.getPropertyValues().addPropertyValue(pv);
}
finally {
this.parseState.pop();
}
}8.解析子元素qualifier
/**
* 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);
}
}
}
/**
* Parse a qualifier element.
*/
public void parseQualifierElement(Element ele, AbstractBeanDefinition bd) {
String typeName = ele.getAttribute(TYPE_ATTRIBUTE);
if (!StringUtils.hasLength(typeName)) {
error("Tag 'qualifier' must have a 'type' attribute", ele);
return;
}
this.parseState.push(new QualifierEntry(typeName));
try {
AutowireCandidateQualifier qualifier = new AutowireCandidateQualifier(typeName);
qualifier.setSource(extractSource(ele));
String value = ele.getAttribute(VALUE_ATTRIBUTE);
if (StringUtils.hasLength(value)) {
qualifier.setAttribute(AutowireCandidateQualifier.VALUE_KEY, value);
}
NodeList nl = ele.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (isCandidateElement(node) && nodeNameEquals(node, QUALIFIER_ATTRIBUTE_ELEMENT)) {
Element attributeEle = (Element) node;
String attributeName = attributeEle.getAttribute(KEY_ATTRIBUTE);
String attributeValue = attributeEle.getAttribute(VALUE_ATTRIBUTE);
if (StringUtils.hasLength(attributeName) && StringUtils.hasLength(attributeValue)) {
BeanMetadataAttribute attribute = new BeanMetadataAttribute(attributeName, attributeValue);
attribute.setSource(extractSource(attributeEle));
qualifier.addMetadataAttribute(attribute);
}
else {
error("Qualifier 'attribute' tag must have a 'name' and 'value'", attributeEle);
return;
}
}
}
bd.addQualifier(qualifier);
}
finally {
this.parseState.pop();
}
}(2) AbstractBeanDefinition属性
上一节中完成了对XML文档到GenericBeanDefinition的转换，GenericBeanDefinition只是AbstractBeanDefinition的子类
public abstract class AbstractBeanDefinition extends BeanMetadataAttributeAccessor
implements BeanDefinition, Cloneable {
//Bean的作用范围，对应的bean属性的scope
private String scope = SCOPE_DEFAULT;
//Bean是否是抽象的
private boolean abstractFlag = false;
//Bean是否延迟加载
private Boolean lazyInit;
//Bean是否自动注入
private int autowireMode = AUTOWIRE_NO;
//Bean是否依赖检查
private int dependencyCheck = DEPENDENCY_CHECK_NONE;
//一个Bean的实例化是否依赖另外一个bean先实例化
private String[] dependsOn;
//容器在查找自动装配对象时，是否考虑该bean
private boolean autowireCandidate = true;
//自动装配出现多个bean候选者时，将作为首选
private boolean primary = false;
//记录子元素的Qualifier
private final Map<String, AutowireCandidateQualifier> qualifiers = new LinkedHashMap<>();
private Supplier<?> instanceSupplier;
//允许访问非公开的构造器和方法
private boolean nonPublicAccessAllowed = true;
//是否以宽松模式解析构造函数
private boolean lenientConstructorResolution = true;
//对应bean属性factory-bean
private String factoryBeanName;
//对应bean属性factory-method
private String factoryMethodName;
//记录构造函数注入属性
private ConstructorArgumentValues constructorArgumentValues;
//普通属性集合
private MutablePropertyValues propertyValues;
//方法重写持有者
private MethodOverrides methodOverrides = new MethodOverrides();
//初始化方法
private String initMethodName;
//销毁方法
private String destroyMethodName;
//是否执行init-method
private boolean enforceInitMethod = true;
//是否执行destory-method
private boolean enforceDestroyMethod = true;
//是否是用户定义
private boolean synthetic = false;
//定义这个bean的应用
private int role = BeanDefinition.ROLE_APPLICATION;
//bean的描述
private String description;
//bean定义的资源
private Resource resource;
}(3)解析默认标签中自定义标签元素
我们用大量的篇幅分析了BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele) 这句代码，接下来要分析 bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
自定义类型的解析
/**
* Decorate the given bean definition through a namespace handler, if applicable.
* @param ele the current element
* @param originalDef the current bean definition
* @return the decorated bean definition
*/
public BeanDefinitionHolder decorateBeanDefinitionIfRequired(Element ele, BeanDefinitionHolder originalDef) {
return decorateBeanDefinitionIfRequired(ele, originalDef, null);
}/**
* Decorate the given bean definition through a namespace handler, if applicable.
* @param ele the current element
* @param originalDef the current bean definition
* @param containingBd the containing bean definition (if any)
* @return the decorated bean definition
*/
public BeanDefinitionHolder decorateBeanDefinitionIfRequired(
Element ele, BeanDefinitionHolder originalDef, @Nullable BeanDefinition containingBd) {
BeanDefinitionHolder finalDefinition = originalDef;
// Decorate based on custom attributes first.
NamedNodeMap attributes = ele.getAttributes();
//遍历所有的属性，看是否有适用于修饰的属性
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();
//遍历所有的子节点，看是否有适用于修饰的子元素
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;
}上面的代码对元素所有的属性和子节点进行了decorateIfRequired()函数的调用，首先获取属性或者元素的命名空间，以此来判断该元素或者属性是否适用于自定义标签的解析条件
/**
* Decorate the given bean definition through a namespace handler,
* if applicable.
* @param node the current child node
* @param originalDef the current bean definition
* @param containingBd the containing bean definition (if any)
* @return the decorated bean definition
*/
public BeanDefinitionHolder decorateIfRequired(
Node node, BeanDefinitionHolder originalDef, @Nullable BeanDefinition containingBd) {
//获取自定义标签的命名空间
String namespaceUri = getNamespaceURI(node);
//对于非默认标签进行修饰
if (namespaceUri != null && !isDefaultNamespace(namespaceUri)) {
//根据命名空间找到对应的处理器
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
if (handler != null) {
//进行修饰
BeanDefinitionHolder decorated =
handler.decorate(node, originalDef, new ParserContext(this.readerContext, this, containingBd));
if (decorated != null) {
return decorated;
}
}
else if (namespaceUri.startsWith("http://www.springframework.org/schema/")) {
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;
}(4)注册解析的BeanDefinition
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry())
完成了配置文件的解析和装饰，需要对Bean进行注册
/**
* 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作为唯一的标识注册
String beanName = definitionHolder.getBeanName();
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// Register aliases for bean name, if any.
// 注册所有的别名
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);
}
}
}1.通过BeanName注册BeanDefinition
（1）对AbstractBeanDefinition的校验
（2）对BeanName已经注册的情况处理
（3）加入Map缓存
（4）清楚解析之前留下的beanName的缓存
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) {
//注册前最后一次校验，对于AbstractBeanDefinition属性中的methodOverride校验
try {
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
//处理已注册的情况
if (existingDefinition != null) {
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
}
else if (existingDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (logger.isInfoEnabled()) {
logger.info("Overriding user-defined bean definition for bean '" + beanName +
"' with a framework-generated bean definition: replacing [" +
existingDefinition + "] with [" + beanDefinition + "]");
}
}
else if (!beanDefinition.equals(existingDefinition)) {
if (logger.isDebugEnabled()) {
logger.debug("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
if (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
//因为beanDefinitionMap是全局变量，这里会存在并发访问情况
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
removeManualSingletonName(beanName);
}
}
else {
// Still in startup registration phase
//注册beanDefinition
this.beanDefinitionMap.put(beanName, beanDefinition);
//记录beanName
this.beanDefinitionNames.add(beanName);
removeManualSingletonName(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (existingDefinition != null || containsSingleton(beanName)) {
//重置所有beanName对应的缓存
resetBeanDefinition(beanName);
}
else if (isConfigurationFrozen()) {
clearByTypeCache();
}
}2.通过别名注册BeanDefinition
（1）对alias与beanName相同时情况处理，不需要处理alias并删除原有alias
（2）alias覆盖处理
（3）alias循环检查
（4）注册alias
public void registerAlias(String name, String alias) {
Assert.hasText(name, "'name' must not be empty");
Assert.hasText(alias, "'alias' must not be empty");
synchronized (this.aliasMap) {
//如果alias与beanName同名，不记录alias
if (alias.equals(name)) {
this.aliasMap.remove(alias);
if (logger.isDebugEnabled()) {
logger.debug("Alias definition '" + alias + "' ignored since it points to same name");
}
}
else {
String registeredName = this.aliasMap.get(alias);
if (registeredName != null) {
if (registeredName.equals(name)) {
// An existing alias - no need to re-register
return;
}
//如果alias不允许覆盖则抛出异常
if (!allowAliasOverriding()) {
throw new IllegalStateException("Cannot define alias '" + alias + "' for name '" +
name + "': It is already registered for name '" + registeredName + "'.");
}
if (logger.isDebugEnabled()) {
logger.debug("Overriding alias '" + alias + "' definition for registered name '" +
registeredName + "' with new target name '" + name + "'");
}
}
//当A->B存在时，若再次出现A->C->B则抛出异常
checkForAliasCircle(name, alias);
this.aliasMap.put(alias, name);
if (logger.isTraceEnabled()) {
logger.trace("Alias definition '" + alias + "' registered for name '" + name + "'");
}
}
}
}二、alias标签的解析
processAliasRegistration()
/**
* Process the given alias element, registering the alias with the registry.
*/
protected void processAliasRegistration(Element ele) {
//获取beanName
String name = ele.getAttribute(NAME_ATTRIBUTE);
//获取alias
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);
}
//别名注册后通知监听器做相应处理
getReaderContext().fireAliasRegistered(name, alias, extractSource(ele));
}
}三、import标签的解析
（1）获取Resource属性所表示的路径
（2）解析路径中的系统属性
（3）判定location是绝对路径还是相对路径
（4）如果是绝对路径递归调用bean的解析过程
（5）如果是相对路径计算出绝对路径进行解析
（6）通知监听器，解析完成
/**
* Parse an "import" element and load the bean definitions
* from the given resource into the bean factory.
*/
protected void importBeanDefinitionResource(Element ele) {
//获取Resource属性
String location = ele.getAttribute(RESOURCE_ATTRIBUTE);
//如果不存在resource属性则不作任何处理
if (!StringUtils.hasText(location)) {
getReaderContext().error("Resource location must not be empty", ele);
return;
}
// Resolve system properties: e.g. "${user.dir}"
// 解析系统属性 "${user.dir}"
location = getReaderContext().getEnvironment().resolveRequiredPlaceholders(location);
Set<Resource> actualResources = new LinkedHashSet<>(4);
// Discover whether the location is an absolute or relative URI
// 判定location是绝对URI还是相对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?
// 绝对URI直接根据地址加载对应的配置文件
if (absoluteLocation) {
try {
int importCount = getReaderContext().getReader().loadBeanDefinitions(location, actualResources);
if (logger.isTraceEnabled()) {
logger.trace("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 {
// 相对URI根据相对地址计算出绝对地市
// 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 {
//如果解析不成功，则使用默认的解析器ResourcePatternResolver进行解析
String baseLocation = getReaderContext().getResource().getURL().toString();
importCount = getReaderContext().getReader().loadBeanDefinitions(
StringUtils.applyRelativePath(baseLocation, location), actualResources);
}
if (logger.isTraceEnabled()) {
logger.trace("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);
}
}
//解析后进行监听器激活处理
Resource[] actResArray = actualResources.toArray(new Resource[0]);
getReaderContext().fireImportProcessed(location, actResArray, extractSource(ele));
}
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