通过 Debug 运行 XmlBeanDefinitionReaderTests 类的 withFreshInputStream() 的方法，调试 Spring 解析 XML 配置文件，获得 Bean 的定义。
大体流程可根据序号查看，xml 配置文件随便看一眼，不用过多在意。
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" "https://www.springframework.org/dtd/spring-beans-2.0.dtd">
<beans>
<bean id="validEmptyWithDescription" class="org.springframework.beans.testfixture.beans.TestBean">
<description>
I have no properties and I'm happy without them.
</description>
</bean>
<!--
Check automatic creation of alias, to allow for names that are illegal as XML ids.
-->
<bean id="aliased" class=" org.springframework.beans.testfixture.beans.TestBean " name="myalias">
<property name="name"><value>aliased</value></property>
</bean>
<alias name="aliased" alias="youralias"/>
<alias name="multiAliased" alias="alias3"/>
<bean id="multiAliased" class="org.springframework.beans.testfixture.beans.TestBean" name="alias1,alias2">
<property name="name"><value>aliased</value></property>
</bean>
<alias name="multiAliased" alias="alias4"/>
<bean class="org.springframework.beans.testfixture.beans.TestBean" name="aliasWithoutId1,aliasWithoutId2,aliasWithoutId3">
<property name="name"><value>aliased</value></property>
</bean>
<bean class="org.springframework.beans.testfixture.beans.TestBean">
<property name="name"><null/></property>
</bean>
<bean class="org.springframework.beans.factory.xml.DummyReferencer"/>
<bean class="org.springframework.beans.factory.xml.DummyReferencer"/>
<bean class="org.springframework.beans.factory.xml.DummyReferencer"/>
<bean id="rod" class="org.springframework.beans.testfixture.beans.TestBean">
<property name="name"><value><!-- a comment -->Rod</value></property>
<property name="age"><value>31</value></property>
<property name="spouse"><ref bean="father"/></property>
<property name="touchy"><value/></property>
</bean>
<bean id="roderick" parent="rod">
<property name="name"><value>Roderick<!-- a comment --></value></property>
<!-- Should inherit age -->
</bean>
<bean id="kerry" class="org.springframework.beans.testfixture.beans.TestBean">
<property name="name"><value>Ker<!-- a comment -->ry</value></property>
<property name="age"><value>34</value></property>
<property name="spouse"><ref bean="rod"/></property>
<property name="touchy"><value></value></property>
</bean>
<bean id="kathy" class="org.springframework.beans.testfixture.beans.TestBean" scope="prototype">
<property name="name"><value>Kathy</value></property>
<property name="age"><value>28</value></property>
<property name="spouse"><ref bean="father"/></property>
</bean>
<bean id="typeMismatch" class="org.springframework.beans.testfixture.beans.TestBean" scope="prototype">
<property name="name"><value>typeMismatch</value></property>
<property name="age"><value>34x</value></property>
<property name="spouse"><ref bean="rod"/></property>
</bean>
<!-- Test of lifecycle callbacks -->
<bean id="mustBeInitialized" class="org.springframework.beans.testfixture.beans.MustBeInitialized"/>
<bean id="lifecycle" class="org.springframework.beans.testfixture.beans.LifecycleBean"
init-method="declaredInitMethod">
<property name="initMethodDeclared"><value>true</value></property>
</bean>
<bean id="protectedLifecycle" class="org.springframework.beans.factory.xml.ProtectedLifecycleBean"
init-method="declaredInitMethod">
<property name="initMethodDeclared"><value>true</value></property>
</bean>
<!-- Factory beans are automatically treated differently -->
<bean id="singletonFactory" class="org.springframework.beans.testfixture.beans.factory.DummyFactory">
</bean>
<bean id="prototypeFactory" class="org.springframework.beans.testfixture.beans.factory.DummyFactory">
<property name="singleton"><value>false</value></property>
</bean>
<!-- Check that the circular reference resolution mechanism doesn't break
repeated references to the same FactoryBean -->
<bean id="factoryReferencer" class="org.springframework.beans.factory.xml.DummyReferencer">
<property name="testBean1"><ref bean="singletonFactory"/></property>
<property name="testBean2"><ref bean="singletonFactory"/></property>
<property name="dummyFactory"><ref bean="&singletonFactory"/></property>
</bean>
<bean id="factoryReferencerWithConstructor" class="org.springframework.beans.factory.xml.DummyReferencer">
<constructor-arg><ref bean="&singletonFactory"/></constructor-arg>
<property name="testBean1"><ref bean="singletonFactory"/></property>
<property name="testBean2"><ref bean="singletonFactory"/></property>
</bean>
<!-- Check that the circular reference resolution mechanism doesn't break
prototype instantiation -->
<bean id="prototypeReferencer" class="org.springframework.beans.factory.xml.DummyReferencer" scope="prototype">
<property name="testBean1"><ref bean="kathy"/></property>
<property name="testBean2"><ref bean="kathy"/></property>
</bean>
<bean id="listenerVeto" class="org.springframework.beans.testfixture.beans.TestBean">
<property name="name"><value>listenerVeto</value></property>
<property name="age"><value>66</value></property>
</bean>
<bean id="validEmpty" class="org.springframework.beans.testfixture.beans.TestBean"/>
<bean id="commentsInValue" class="org.springframework.beans.testfixture.beans.TestBean">
<property name="name"><value>this is<!-- don't mind me --> a <![CDATA[<!--comment-->]]></value></property>
</bean>
</beans>
@Test
public void withFreshInputStream() {
// TODO 1.创建 SimpleBeanDefinitionRegistry 对象，提供注册BeanDefinition功能
SimpleBeanDefinitionRegistry registry = new SimpleBeanDefinitionRegistry();
// TODO 2.获取配置文件
Resource resource = new ClassPathResource("test.xml", getClass());
// TODO 3.创建 XmlBeanDefinitionReader 对象，提供读取 XMl 文件中的 Bean 的定义信息；
new XmlBeanDefinitionReader(registry).loadBeanDefinitions(resource);
// TODO 30.验证 BeanDefinitions 信息；
testBeanDefinitions(registry);
System.out.println("success");
}
private void testBeanDefinitions(BeanDefinitionRegistry registry) {
assertThat(registry.getBeanDefinitionCount()).isEqualTo(24);
assertThat(registry.getBeanDefinitionNames().length).isEqualTo(24);
assertThat(Arrays.asList(registry.getBeanDefinitionNames()).contains("rod")).isTrue();
assertThat(Arrays.asList(registry.getBeanDefinitionNames()).contains("aliased")).isTrue();
assertThat(registry.containsBeanDefinition("rod")).isTrue();
assertThat(registry.containsBeanDefinition("aliased")).isTrue();
assertThat(registry.getBeanDefinition("rod").getBeanClassName()).isEqualTo(TestBean.class.getName());
assertThat(registry.getBeanDefinition("aliased").getBeanClassName()).isEqualTo(TestBean.class.getName());
assertThat(registry.isAlias("youralias")).isTrue();
String[] aliases = registry.getAliases("aliased");
assertThat(aliases.length).isEqualTo(2);
assertThat(ObjectUtils.containsElement(aliases, "myalias")).isTrue();
assertThat(ObjectUtils.containsElement(aliases, "youralias")).isTrue();
}
/**
* Load bean definitions from the specified XML file.
* @param resource the resource descriptor for the XML file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
*
* TODO XmlBeanDefinitionReader加载资源的入口方法
*/
@Override
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
// TODO 4.将读取的XML资源进行特殊的编码处理
return loadBeanDefinitions(new EncodedResource(resource));
}
/**
* Load bean definitions from the specified XML file.
* @param encodedResource the resource descriptor for the XML file,
* allowing to specify an encoding to use for parsing the file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
*
* TODO 这里载入XML形式Bean配置信息方法
*/
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isTraceEnabled()) {
logger.trace("Loading XML bean definitions from " + encodedResource);
}
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
}
// TODO 5. 将资源文件转为InputStream的I/O流
try (InputStream inputStream = encodedResource.getResource().getInputStream()) { // TODO 只有是Closeable的子类才能这样书写，有点是系统会自动帮助我们关闭
// TODO 从InputStream中得到XML的解析源
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
// TODO 6.具体读取过程
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"IOException parsing XML document from " + encodedResource.getResource(), ex);
}
finally {
// TODO 29.
currentResources.remove(encodedResource);
if (currentResources.isEmpty()) {
this.resourcesCurrentlyBeingLoaded.remove();
}
}
}
/**
* Actually load bean definitions from the specified XML file.
* @param inputSource the SAX InputSource to read from
* @param resource the resource descriptor for the XML file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
* @see #doLoadDocument
* @see #registerBeanDefinitions
*
*
*/
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
// TODO 7. 加载Bean配置信息，并转换为文档对象
Document doc = doLoadDocument(inputSource, resource);
// TODO 8. 对Bean定义进行解析
int count = registerBeanDefinitions(doc, resource);
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + count + " bean definitions from " + resource);
}
return count;
}
catch (BeanDefinitionStoreException ex) {
throw ex;
}
catch (SAXParseException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
}
catch (SAXException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"XML document from " + resource + " is invalid", ex);
}
catch (ParserConfigurationException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Parser configuration exception parsing XML from " + resource, ex);
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"IOException parsing XML document from " + resource, ex);
}
catch (Throwable ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Unexpected exception parsing XML document from " + resource, ex);
}
}
/**
* Register the bean definitions contained in the given DOM document.
* Called by {@code loadBeanDefinitions}.
* <p>Creates a new instance of the parser class and invokes
* {@code registerBeanDefinitions} on it.
* @param doc the DOM document
* @param resource the resource descriptor (for context information)
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of parsing errors
* @see #loadBeanDefinitions
* @see #setDocumentReaderClass
* @see BeanDefinitionDocumentReader#registerBeanDefinitions
*
* TODO 按照Spring的Bean语义要求将Bean配置信息解析并转换为内部数据结构
*
*/
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
// TODO 9.得到BeanDefinitionDoucumentReader来对XML格式的BeanDefinition进行解析
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
// TODO 10.获得容器中注册的Bean数量
int countBefore = getRegistry().getBeanDefinitionCount();
// TODO 11. 解析过程的入口，这里使用了委派模式，BeanDefinitionDocumentReader只是一个接口
// TODO 具体的解析过程由实现类DefaultBeanDefinitionDocumentReader完成
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
// TODO 28. 统计解析的Bean数量
return getRegistry().getBeanDefinitionCount() - countBefore;
}
/**
* This implementation parses bean definitions according to the "spring-beans" XSD
* (or DTD, historically).
* <p>Opens a DOM Document; then initializes the default settings
* specified at the {@code <beans/>} level; then parses the contained bean definitions.
*
* TODO 根据Spring DTD对Bean的定义规则解析Bean定义的文档对象
*/
@Override
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
// TODO 获得XML描述符
this.readerContext = readerContext;
// TODO 12. doc.getDocumentElement() 获的Document根元素
doRegisterBeanDefinitions(doc.getDocumentElement());
}
/**
* Register each bean definition within the given root {@code <beans/>} element.
*/
@SuppressWarnings("deprecation") // for Environment.acceptsProfiles(String...)
protected void doRegisterBeanDefinitions(Element root) {
// Any nested <beans> elements will cause recursion in this method. In
// order to propagate and preserve <beans> default-* attributes correctly,
// keep track of the current (parent) delegate, which may be null. Create
// the new (child) delegate with a reference to the parent for fallback purposes,
// then ultimately reset this.delegate back to its original (parent) reference.
// this behavior emulates a stack of delegates without actually necessitating one.
// TODO 具体的解析过程由BeanDefinitionParserDelegate实现
// TODO BeanDefinitionParserDelegate中定义了Spring Bean定义XML文件的各元素
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(getReaderContext(), root, parent);
// TODO 校验是否引入 beans schemaLocation
if (this.delegate.isDefaultNamespace(root)) {
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
if (StringUtils.hasText(profileSpec)) {
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
// We cannot use Profiles.of(...) since profile expressions are not supported
// in XML config. See SPR-12458 for details.
if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
if (logger.isDebugEnabled()) {
logger.debug("Skipped XML bean definition file due to specified profiles [" + profileSpec +
"] not matching: " + getReaderContext().getResource());
}
return;
}
}
}
// TODO 在解析Bean定义之前，进行自定义解析，增强解析过程的可扩展性
preProcessXml(root);
// TODO 12.从文档的根元素开始进行Bean定义的文档对象的解析
parseBeanDefinitions(root, this.delegate);
// TODO 27.在解析Bean定义之后，进行自定义解析，增强解析过程的可扩展性
postProcessXml(root);
this.delegate = parent;
}
/**
* Parse the elements at the root level in the document:
* "import", "alias", "bean".
* @param root the DOM root element of the document
*
* TODO 使用Spring的Bean规则从文档的根元素开始Bean定义的文档对象的解析
*/
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
// TODO 13. Bean定义的文档对象使用了Spring默认的XML命名空间
if (delegate.isDefaultNamespace(root)) {
// TODO 14. 获取Bean定义的文档对象根元素的所有子节点
NodeList nl = root.getChildNodes();
// TODO 此处是循环,忽略需要，需要是大体执行流程不是唯一
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
// TODO 15. 获得的文档节点是XML元素节点
if (node instanceof Element ele) {
// TODO 16. Bean定义的文档的元素节点使用的是Spring默认的XML命名空间
if (delegate.isDefaultNamespace(ele)) {
// TODO 17. 使用Spring的Bean规则解析元素节点
parseDefaultElement(ele, delegate);
}
else {
// TODO 如果没有使用Spring默认的XMl命名空间，则使用用户自定义的规则解析元素节点
delegate.parseCustomElement(ele);
}
}
}
}
else {
// TODO 如果没有使用Spring默认的XMl命名空间，则使用用户自定义的规则解析元素节点
delegate.parseCustomElement(root);
}
}
/**
* TODO 使用Spring的Bean规则解析文档元素节点
* @param ele
* @param delegate
*/
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
// TODO 18.如果节点是<import>导入元素，进行导入元素解析
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
// TODO 19.如果节点是<alias>别名元素，进行别名解析
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
// TODO 20.如果节点是<bean>元素，则按照Spring的Bean规则解析元素
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
// TODO 如果节点是<beans>元素，则按照Spring的Bean规则解析元素
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.
* TODO 解析Bean资源文档对象的普通元素
* TODO 示例：<bean id="testBean" class="org.springframework.beans.testfixture.beans.TestBean"/>
*/
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
// TODO 21. BeanDefinitionHolder是对BeanDefinition的封装，即Bean定义的封装类
// TODO 对文档对象中<bean>元素的解析由BeanDefinitionParserDelegate实现
// TODO BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// 22.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.
// TODO 26.在完成向Spring Ioc容器注册解析得到的Bean定义之后，发送注册事件
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
/**
* 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
*
* TODO 将解析的BeanDefinitionHole注册到Spring Ioc容器
*/
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
// Register bean definition under primary name.
// TODO 获取解析的beanDefinition的名称
String beanName = definitionHolder.getBeanName();
// TODO 23.向Spring Ioc容器注册BeanDefinition
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// Register aliases for bean name, if any.
// TODO 25.如果解析的BeanDefinition有别名，向Spring Ioc容器注册别名
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);
}
}
}
/**
* TODO 注册 BeanDefinition 信息
*/
@Override
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException {
Assert.hasText(beanName, "'beanName' must not be empty");
Assert.notNull(beanDefinition, "BeanDefinition must not be null");
// TODO 24.存储 BeanDefinition
this.beanDefinitionMap.put(beanName, beanDefinition);
}
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