xml解析之默认标签解析
接上篇通过xml文件加载BeanDefinition (opens new window)
默认标签解析方法封装在DefaultBeanDefinitionDocumentReader#parseDefaultElement
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
//解析import标签
importBeanDefinitionResource(ele);
}
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
//解析alias标签
processAliasRegistration(ele);
}
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
//解析bean标签
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// 嵌套 递归调用 DefaultBeanDefinitionDocumentReader.doRegisterBeanDefinitions
doRegisterBeanDefinitions(ele);
}
}
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# 解析import
<import resource="classpath:applicationContext-dao-config.xml" />
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protected void importBeanDefinitionResource(Element ele) {
//获取配置文件地址
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}"
//占位符替换
location = getReaderContext().getEnvironment().resolveRequiredPlaceholders(location);
Set<Resource> actualResources = new LinkedHashSet<>(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 {
//解析导入的资源文件 还是使用XmlBeanDefinitionReader.loadBeanDefinitions来完成
int importCount = getReaderContext().getReader().loadBeanDefinitions(location, actualResources);
}
//...
}
else {
// No URL -> considering resource location as relative to the current file.
//相对地址
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);
}
}
//..
}
Resource[] actResArray = actualResources.toArray(new Resource[0]);
getReaderContext().fireImportProcessed(location, actResArray, extractSource(ele));
}
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总结下来就是获取到资源文件的地址，然后调用XmlBeanDefinitionReader.loadBeanDefinitions对导入的资源文件进行解析
解析完导入文件后，spring还会发布一个消息，监听器是XmlBeanDefinitionReader.eventListener
private ReaderEventListener eventListener = new EmptyReaderEventListener();
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默认是一个空实现，会丢弃消息不处理，也可以自定义实现ReaderEventListener，如CollectingReaderEventListener
从上文可知XmlBeanDefinitionReader的创建是在AbstractXmlApplicationContext#loadBeanDefinitions(DefaultListableBeanFactory)中完成，
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
initBeanDefinitionReader(beanDefinitionReader);
loadBeanDefinitions(beanDefinitionReader);
}
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如果使用自定义的监听器，则需手动设置,并主动刷新容器。
//使用GenericApplicationContext是因为它在刷新容器时不会再解析配置文件，
GenericApplicationContext context = new GenericApplicationContext();
XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(context);
//CollectingReaderEventListener位于testfixture包中，此处只是举例
reader.setEventListener(new CollectingReaderEventListener());
reader.loadBeanDefinitions("services.xml", "daos.xml");
context.refresh();
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# 解析alias
<alias name="myApp-dataSource" alias="subsystemA-dataSource"/>
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protected void processAliasRegistration(Element ele) {
String name = ele.getAttribute(NAME_ATTRIBUTE);
String alias = ele.getAttribute(ALIAS_ATTRIBUTE);
boolean valid = true;
//...
if (valid) {
try {
//获取BeanDefinitionRegistry，记录别名
getReaderContext().getRegistry().registerAlias(name, alias);
}
//...
//发布解析别名消息
getReaderContext().fireAliasRegistered(name, alias, extractSource(ele));
}
}
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# 解析bean
xml格式，具体可查看Spring官方文档 (opens new window)
<bean id="clientService" class="examples.ClientService" factory-method="createInstance"/>
<bean id="beanOne" class="x.y.ThingOne">
<constructor-arg ref="beanTwo"/>
<constructor-arg ref="beanThree"/>
<constructor-arg index="0" value="7500000"/>
<constructor-arg index="1" value="42"/>
<constructor-arg name="years" value="7500000"/>
<constructor-arg name="ultimateAnswer" value="42"/>
</bean>
<bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
<!-- results in a setDriverClassName(String) call -->
<property name="driverClassName" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mydb"/>
<property name="username" value="root"/>
<property name="password" value="misterkaoli"/>
</bean>
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protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
//解析Bean并包装到BeanDefinitionHolder中
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
//解析bean标签中的自定义标签
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// 注册到bean定义中心
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// 发布事件消息
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
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public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
//id
String id = ele.getAttribute(ID_ATTRIBUTE);
//name 别名
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
List<String> aliases = new ArrayList<>();
if (StringUtils.hasLength(nameAttr)) {
//别名可以多个，以,或;分隔
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) {
//检查不能重复
checkNameUniqueness(beanName, aliases, ele);
}
//生成BeanDefinition
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
if (!StringUtils.hasText(beanName)) {
//没有指定beanName也没有指定别名，生成一个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);
}
}
}
catch (Exception ex) {
error(ex.getMessage(), ele);
return null;
}
}
String[] aliasesArray = StringUtils.toStringArray(aliases);
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
return null;
}
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public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, @Nullable BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
String className = null;
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();//解析class属性
}
String parent = null;
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);//解析parent属性
}
try {
AbstractBeanDefinition bd = createBeanDefinition(className, parent);//创建BeanDefinition
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);//解析bean属性
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
parseMetaElements(ele, bd);//解析元数据
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());//解析lookup-method
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());//解析replaced-method
parseConstructorArgElements(ele, bd);//解析构造方法
parsePropertyElements(ele, bd);//解析property子元素
parseQualifierElements(ele, bd);//解析qualifier子元素
bd.setResource(this.readerContext.getResource());//
bd.setSource(extractSource(ele));
return bd;
}
//...
return null;
}
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lookup methodj介绍 (opens new window)
replace method介绍 (opens new window)
回到processBeanDefinition方法，初步创建BeanDefinition，之后还会处理bean标签中的自定义标签，这部分的内容放在xml解析之自定义标签解析 (opens new window)
编辑 (opens new window)
上次更新: 2023/04/09, 16:34:32