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曹工说Spring Boot源码（6）-- Spring怎么从xml文件里解析bean的

写在前面的话#

相关背景及资源：

曹工说 Spring Boot 源码（1）-- Bean Definition 到底是什么，附 spring 思维导图分享

曹工说 Spring Boot 源码（2）-- Bean Definition 到底是什么，咱们对着接口，逐个方法讲解

曹工说 Spring Boot 源码（3）-- 手动注册 Bean Definition 不比游戏好玩吗，我们来试一下

曹工说 Spring Boot 源码（4）-- 我是怎么自定义 ApplicationContext，从 json 文件读取 bean definition 的？

曹工说 Spring Boot 源码（5）-- 怎么从 properties 文件读取 bean

工程代码地址 思维导图地址

工程结构图：

整体流程#

这次，我们打算讲一下，spring 启动时，是怎么去读取 xml 文件的，bean 的解析部分可能暂时涉及不到，因为放到一起，内容就太多了，具体再看吧。

  1. 给ClassPathXmlApplicationContext设置 xml 文件的路径

  2. refresh内部的beanFactory，其实这时候BeanFactory都还没创建，会先创DefaultListableBeanFactory

  3. ClassPathXmlApplicationContext调用其loadBeanDefinitions，将新建DefaultListableBeanFactory作为参数传入

  4. ClassPathXmlApplicationContext内部会持有一个XmlBeanDefinitionReader，且XmlBeanDefinitionReader内部是持有之前创建的DefaultListableBeanFactory的，这时候就简单了，XmlBeanDefinitionReader负责读取 xml，将bean definition 解析出来，丢给DefaultListableBeanFactory，此时，XmlBeanDefinitionReader就算完成了，退出历史舞台

  5. 上面第四步完成后，DefaultListableBeanFactory里面其实一个业务 bean 都没有，只有一堆的 bean definition，后面ClassPathXmlApplicationContext直接去实例化那些需要在启动过程中实例化的 bean。

    当前，这中间还涉及到使用beanDefinitionPostProcessor和beanPostProcessor对 beanFactory 进行处理，这都是后话了。

这次，我们主要讲的部分是，第 4 步。

入口代码#

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位置：org.springframework.context.support.AbstractRefreshableApplicationContext

<span class="token annotation punctuation">@Override</span>
<span class="token keyword">protected</span> <span class="token keyword">final</span> <span class="token keyword">void</span> <span class="token function">refreshBeanFactory</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">BeansException</span> <span class="token punctuation">{</span>
	<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">hasBeanFactory</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
		<span class="token function">destroyBeans</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token function">closeBeanFactory</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>
	<span class="token keyword">try</span> <span class="token punctuation">{</span>
		<span class="token comment">//创建一个DefaultListableBeanFactory</span>
		<span class="token class-name">DefaultListableBeanFactory</span> beanFactory <span class="token operator">=</span> <span class="token function">createBeanFactory</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		beanFactory<span class="token punctuation">.</span><span class="token function">setSerializationId</span><span class="token punctuation">(</span><span class="token function">getId</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token function">customizeBeanFactory</span><span class="token punctuation">(</span>beanFactory<span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token comment">// 加载</span>
		<span class="token function">loadBeanDefinitions</span><span class="token punctuation">(</span>beanFactory<span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token keyword">synchronized</span> <span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span>beanFactoryMonitor<span class="token punctuation">)</span> <span class="token punctuation">{</span>
			<span class="token keyword">this</span><span class="token punctuation">.</span>beanFactory <span class="token operator">=</span> beanFactory<span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
	<span class="token punctuation">}</span>
	<span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">IOException</span> ex<span class="token punctuation">)</span> <span class="token punctuation">{</span>
		<span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">ApplicationContextException</span><span class="token punctuation">(</span><span class="token string">"I/O error parsing bean definition source for "</span> <span class="token operator">+</span> <span class="token function">getDisplayName</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> ex<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>
<span class="token punctuation">}</span>

上面调用了

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AbstractXmlApplicationContext#loadBeanDefinitions(org.springframework.beans.factory.support.DefaultListableBeanFactory)

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protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) {
		// 创建一个从 xml 读取 beanDefinition 的读取器
		XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

	<span class="token comment">// 配置环境</span>
	beanDefinitionReader<span class="token punctuation">.</span><span class="token function">setEnvironment</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">getEnvironment</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token comment">// 配置资源loader，一般就是classpathx下去获取xml</span>
	beanDefinitionReader<span class="token punctuation">.</span><span class="token function">setResourceLoader</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token comment">// xml解析的解析器</span>
	beanDefinitionReader<span class="token punctuation">.</span><span class="token function">setEntityResolver</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">ResourceEntityResolver</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

	<span class="token comment">// Allow a subclass to provide custom initialization of the reader,</span>
	<span class="token comment">// then proceed with actually loading the bean definitions.</span>
	<span class="token function">initBeanDefinitionReader</span><span class="token punctuation">(</span>beanDefinitionReader<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token comment">// 核心方法，使用beanDefinitionReader去解析xml，并将解析后的bean definition放到beanFactory</span>
	<span class="token function">loadBeanDefinitions</span><span class="token punctuation">(</span>beanDefinitionReader<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

xml 中 xsd、dtd 解析器#

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// xml 解析的解析器
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

这个类实现的接口就是 jdk 里面的org.xml.sax.EntityResolver，这个接口，只有一个方法，主要负责 xml 里，外部实体的解析：

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public interface EntityResolver {

<span class="token keyword">public</span> <span class="token keyword">abstract</span> <span class="token class-name">InputSource</span> resolveEntity <span class="token punctuation">(</span><span class="token class-name">String</span> publicId<span class="token punctuation">,</span>
                                           <span class="token class-name">String</span> systemId<span class="token punctuation">)</span>
    <span class="token keyword">throws</span> <span class="token class-name">SAXException</span><span class="token punctuation">,</span> <span class="token class-name">IOException</span><span class="token punctuation">;</span>



}

大家可能不太明白，我们看看怎么实现的吧：

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public class DelegatingEntityResolver implements EntityResolver {

<span class="token comment">/** Suffix for DTD files */</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">DTD_SUFFIX</span> <span class="token operator">=</span> <span class="token string">".dtd"</span><span class="token punctuation">;</span>

<span class="token comment">/** Suffix for schema definition files */</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">XSD_SUFFIX</span> <span class="token operator">=</span> <span class="token string">".xsd"</span><span class="token punctuation">;</span>


<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">EntityResolver</span> dtdResolver<span class="token punctuation">;</span>

<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">EntityResolver</span> schemaResolver<span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token class-name">DelegatingEntityResolver</span><span class="token punctuation">(</span><span class="token class-name">ClassLoader</span> classLoader<span class="token punctuation">)</span> <span class="token punctuation">{</span>
	<span class="token keyword">this</span><span class="token punctuation">.</span>dtdResolver <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BeansDtdResolver</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">this</span><span class="token punctuation">.</span>schemaResolver <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">PluggableSchemaResolver</span><span class="token punctuation">(</span>classLoader<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token comment">// 主要看这里，感觉就是对我们xml里面的那堆xsd进行解析</span>
<span class="token annotation punctuation">@override</span>  
<span class="token keyword">public</span> <span class="token class-name">InputSource</span> <span class="token function">resolveEntity</span><span class="token punctuation">(</span><span class="token class-name">String</span> publicId<span class="token punctuation">,</span> <span class="token class-name">String</span> systemId<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">SAXException</span><span class="token punctuation">,</span> <span class="token class-name">IOException</span> <span class="token punctuation">{</span>
	<span class="token keyword">if</span> <span class="token punctuation">(</span>systemId <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
		<span class="token keyword">if</span> <span class="token punctuation">(</span>systemId<span class="token punctuation">.</span><span class="token function">endsWith</span><span class="token punctuation">(</span><span class="token constant">DTD_SUFFIX</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
			<span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>dtdResolver<span class="token punctuation">.</span><span class="token function">resolveEntity</span><span class="token punctuation">(</span>publicId<span class="token punctuation">,</span> systemId<span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
		<span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>systemId<span class="token punctuation">.</span><span class="token function">endsWith</span><span class="token punctuation">(</span><span class="token constant">XSD_SUFFIX</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
			<span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>schemaResolver<span class="token punctuation">.</span><span class="token function">resolveEntity</span><span class="token punctuation">(</span>publicId<span class="token punctuation">,</span> systemId<span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
	<span class="token punctuation">}</span>
	<span class="token keyword">return</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

举个例子，我们 xml 里一般不是有如下代码吗：

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<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
				http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">

上面的代码，应该就是去获取和解析上面这里的xsd，方便进行语法校验的。毕竟，这个 xml 我们也不能随便乱写吧，比如，根元素就是，有且 只能有一个，下面才能有 0 到多个之类的元素。你要是写了多个根元素，肯定不合规范啊。

接下来，我们还是赶紧切入正题吧，看看XmlBeanDefinitionReader是怎么解析 xml 的。

XmlBeanDefinitionReader 解析 xml#

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protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
		Resource[] configResources = getConfigResources();
		if (configResources != null) {
			reader.loadBeanDefinitions(configResources);
		}
		String[] configLocations = getConfigLocations();
    	// 这个方法还在：AbstractXmlApplicationContext，获取资源位置，传给 XmlBeanDefinitionReader
		if (configLocations != null) {
			reader.loadBeanDefinitions(configLocations);
		}
	}

经过几个简单跳转，进入下面的方法：

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org.springframework.beans.factory.support.AbstractBeanDefinitionReader#loadBeanDefinitions(java.lang.String, java.util.Set<org.springframework.core.io.Resource>)

public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
ResourceLoader resourceLoader = getResourceLoader();


	<span class="token keyword">if</span> <span class="token punctuation">(</span>resourceLoader <span class="token keyword">instanceof</span> <span class="token class-name">ResourcePatternResolver</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
		<span class="token keyword">try</span> <span class="token punctuation">{</span>
			<span class="token class-name">Resource</span><span class="token punctuation">[</span><span class="token punctuation">]</span> resources <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token class-name">ResourcePatternResolver</span><span class="token punctuation">)</span> resourceLoader<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getResources</span><span class="token punctuation">(</span>location<span class="token punctuation">)</span><span class="token punctuation">;</span>
              <span class="token comment">// 从资源数组里load bean definition</span>
			<span class="token keyword">int</span> loadCount <span class="token operator">=</span> <span class="token function">loadBeanDefinitions</span><span class="token punctuation">(</span>resources<span class="token punctuation">)</span><span class="token punctuation">;</span>
			<span class="token keyword">return</span> loadCount<span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
	<span class="token punctuation">}</span>
	
<span class="token punctuation">}</span>

XmlBeanDefinitionReader 类图#

这里插一句，看看其类图：

总的来说，类似于模板设计模式，一些通用的逻辑和流程，放在AbstractBeanDefinitionReader, 具体的解析啊，都是放在子类实现。

我们这里也可以看到，其实现了一个接口，BeanDefinitionReader：

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package org.springframework.beans.factory.support;

public interface BeanDefinitionReader {
// 为什么需要这个，因为读取到 bean definition 后，需要存到这个里面去；如果不提供这个，我读了往哪放
BeanDefinitionRegistry getRegistry();
// 资源加载器，加载 xml 之类，当然，作为一个接口，资源是可以来自于任何地方
ResourceLoader getResourceLoader();
// 获取 classloader
ClassLoader getBeanClassLoader();
// beanName 生成器
BeanNameGenerator getBeanNameGenerator();
// 从资源 load bean definition
int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException;


<span class="token keyword">int</span> <span class="token function">loadBeanDefinitions</span><span class="token punctuation">(</span><span class="token class-name">Resource</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> resources<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">BeanDefinitionStoreException</span><span class="token punctuation">;</span>

<span class="token keyword">int</span> <span class="token function">loadBeanDefinitions</span><span class="token punctuation">(</span><span class="token class-name">String</span> location<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">BeanDefinitionStoreException</span><span class="token punctuation">;</span>

<span class="token keyword">int</span> <span class="token function">loadBeanDefinitions</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> locations<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">BeanDefinitionStoreException</span><span class="token punctuation">;</span>



}

我们切回前面，AbstractBeanDefinitionReader实现了大部分方法，除了下面这个：

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	int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException;

因为，它毕竟只是个抽象类，不负责干活啊；而且，为了能够从不同的 resource 读取，这个也理应交给子类。

比如，我们这里的XmlBeanDefinitionReader就是负责从 xml 文件读取；我之前的文章里，也演示了如何从 json 读取，也是自定义了一个AbstractBeanDefinitionReader的子类。

读取 xml 文件为 InputSource#

接着上面的方法往下走，马上就进入到了：

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位置：org.springframework.beans.factory.xml.XmlBeanDefinitionReader，插入的参数，就是我们的xml
public int loadBeanDefinitions(EncodedResource encodedResource)  {
		...
		try {
			// 读取 xml 文件为文件流
			InputStream inputStream = encodedResource.getResource().getInputStream();
			try {
				// 读取为 xml 资源
				InputSource inputSource = new InputSource(inputStream);
				if (encodedResource.getEncoding() != null) {
					inputSource.setEncoding(encodedResource.getEncoding());
				}
				// 解析 bean definition 去
				return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
			}
		}
	}

这里，提一句InputSource，这个类的全路径为：org.xml.sax.InputSource，是 jdk 里的类。

包名里包括了 xml，知道大概是 xml 相关的类了，包名也包含了 sax，大概知道是基于 sax 事件解析模型。

这方面我懂得也不多，回头可以单独讲解。我们继续正文：

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protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) {
		try {
			int validationMode = getValidationModeForResource(resource);
             // 反正 org.w3c.dom.Document 也是 jdk 的类，具体不管
			Document doc = this.documentLoader.loadDocument(
					inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());
             // 下边就开始正题了 
			return registerBeanDefinitions(doc, resource);
		}
	}

关于documentLoader.loadDocument，大家只要简单知道，是进行初步的解析就行了，主要是基于 xsd、dtd 等，进行语法检查等。

我这里的堆栈，大家看下：

这里，先不深究 xml 解析的东西（主要是我也不怎么会啊，哈哈哈）

接着走：

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	public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		documentReader.setEnvironment(this.getEnvironment());
		int countBefore = getRegistry().getBeanDefinitionCount();
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		return getRegistry().getBeanDefinitionCount() - countBefore;
	}

BeanDefinitionDocumentReader#

看得出来，XmlBeanDefinitionReader可能觉得工作繁重，于是将具体的工作，交给了BeanDefinitionDocumentReader。

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public interface BeanDefinitionDocumentReader {

<span class="token keyword">void</span> <span class="token function">setEnvironment</span><span class="token punctuation">(</span><span class="token class-name">Environment</span> environment<span class="token punctuation">)</span><span class="token punctuation">;</span>


<span class="token keyword">void</span> <span class="token function">registerBeanDefinitions</span><span class="token punctuation">(</span><span class="token class-name">Document</span> doc<span class="token punctuation">,</span> <span class="token class-name">XmlReaderContext</span> readerContext<span class="token punctuation">)</span>
		<span class="token keyword">throws</span> <span class="token class-name">BeanDefinitionStoreException</span><span class="token punctuation">;</span>



}

核心方法肯定是

void registerBeanDefinitions(Document doc, XmlReaderContext readerContext)

两个参数，Document我们理解，就是代表 xml 文件；

XmlReaderContext#

XmlReaderContext是啥，看样子是个上下文，上下文，一般来说，就是个大杂烩，把需要用到的都会放在里面。

我们看看放了些啥：

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public class XmlReaderContext extends ReaderContext {
	// 之前的核心类，把自己传进来了
	private final XmlBeanDefinitionReader reader;
	// org.springframework.beans.factory.xml.NamespaceHandlerResolver，这个也是核心类！
	private final NamespaceHandlerResolver namespaceHandlerResolver;
}

public class ReaderContext {
//xml 资源本身
private final Resource resource;
// 盲猜是中间处理报错后，报告问题
private final ProblemReporter problemReporter;
// event/listener 机制吧，方便扩展
private final ReaderEventListener eventListener;`
// 跳过
private final SourceExtractor sourceExtractor;
}

看完了这个上下文的定义，要知道，它是作为一个参数，传给：

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org.springframework.beans.factory.xml.BeanDefinitionDocumentReader
void registerBeanDefinitions(Document doc, XmlReaderContext readerContext)
			throws BeanDefinitionStoreException;

那，这个参数怎么构造的呢？

那，我们还得切回前面的代码：

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public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		documentReader.setEnvironment(this.getEnvironment());
		int countBefore = getRegistry().getBeanDefinitionCount();
    	// 这里，调用 createReaderContext(resource) 创建上下文
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		return getRegistry().getBeanDefinitionCount() - countBefore;
	}

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	/**
	 * Create the {@link XmlReaderContext} to pass over to the document reader.
	 */
	protected XmlReaderContext createReaderContext(Resource resource) {
		if (this.namespaceHandlerResolver == null) {
             // 创建一个 namespacehandler
			this.namespaceHandlerResolver = createDefaultNamespaceHandlerResolver();
		}
		return new XmlReaderContext(resource, this.problemReporter, this.eventListener,
				this.sourceExtractor, this, this.namespaceHandlerResolver);
	}

namespaceHandlerResolver#

这里太核心了，我们看看namespaceHandlerResolver是干嘛的：

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public interface NamespaceHandlerResolver {

<span class="token comment">/**
 * Resolve the namespace URI and return the located {@link NamespaceHandler}
 * implementation.
 * @param namespaceUri the relevant namespace URI
 * @return the located {@link NamespaceHandler} (may be {@code null})
 */</span>
<span class="token comment">// 比如解析xml时，我们可能有&lt;bean&gt;，这个是默认命名空间，其namespace就是&lt;beans&gt;;如果是&lt;context:component-scan&gt;，这里的namespace，就是context</span>
<span class="token class-name">NamespaceHandler</span> <span class="token function">resolve</span><span class="token punctuation">(</span><span class="token class-name">String</span> namespaceUri<span class="token punctuation">)</span><span class="token punctuation">;</span>



}

这个类的用途，就是根据传入的 namespace，找到对应的 handler。

大家可以去 spring-beans.jar 包里的META-INF/spring.handlers找一找，这个文件打开后，内容如下：

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http\://www.springframework.org/schema/c=org.springframework.beans.factory.xml.SimpleConstructorNamespaceHandler
http\://www.springframework.org/schema/p=org.springframework.beans.factory.xml.SimplePropertyNamespaceHandler
http\://www.springframework.org/schema/util=org.springframework.beans.factory.xml.UtilNamespaceHandler

也可以再去 spring-context.jar 里找找，里面也有这个文件：

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http\://www.springframework.org/schema/context=org.springframework.context.config.ContextNamespaceHandler
http\://www.springframework.org/schema/jee=org.springframework.ejb.config.JeeNamespaceHandler
http\://www.springframework.org/schema/lang=org.springframework.scripting.config.LangNamespaceHandler
http\://www.springframework.org/schema/task=org.springframework.scheduling.config.TaskNamespaceHandler
http\://www.springframework.org/schema/cache=org.springframework.cache.config.CacheNamespaceHandler

我列了个表格：

namespace handler
http://www.springframework.org/schema/c org.springframework.beans.factory.xml.SimpleConstructorNamespaceHandler
http://www.springframework.org/schema/p org.springframework.beans.factory.xml.SimplePropertyNamespaceHandler
http://www.springframework.org/schema/util org.springframework.beans.factory.xml.UtilNamespaceHandler
http://www.springframework.org/schema/context org.springframework.context.config.ContextNamespaceHandler
http://www.springframework.org/schema/task org.springframework.scheduling.config.TaskNamespaceHandler
http://www.springframework.org/schema/cache org.springframework.cache.config.CacheNamespaceHandler

比较重要的，我都列在上面了，剩下的jee/lang，我没用过，不知道大家用过没，先跳过吧。

大家可能也有感到奇怪的地方，怎么没有这个 namespace 的呢，因为它是默认的，所以在程序里是特殊处理的，一会才到它。

接着看核心逻辑：

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DefaultBeanDefinitionDocumentReader#doRegisterBeanDefinitions
protected void doRegisterBeanDefinitions(Element root) {
		BeanDefinitionParserDelegate parent = this.delegate;
		this.delegate = createHelper(this.readerContext, root, parent);

	<span class="token function">preProcessXml</span><span class="token punctuation">(</span>root<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token function">parseBeanDefinitions</span><span class="token punctuation">(</span>root<span class="token punctuation">,</span> <span class="token keyword">this</span><span class="token punctuation">.</span>delegate<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token function">postProcessXml</span><span class="token punctuation">(</span>root<span class="token punctuation">)</span><span class="token punctuation">;</span>

	<span class="token keyword">this</span><span class="token punctuation">.</span>delegate <span class="token operator">=</span> parent<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

BeanDefinitionParserDelegate#

恩。。。我们已经快疯了，怎么又出来一个类，DefaultBeanDefinitionDocumentReader看来也是觉得自己工作压力太大了吧，这里又弄了个BeanDefinitionParserDelegate。

这个类，没实现什么接口，就是个大杂烩，方法多的一批，主要是进行具体的解析工作，大家可以看看里面定义的字段：

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	public static final String BEANS_NAMESPACE_URI = "http://www.springframework.org/schema/beans";

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">MULTI_VALUE_ATTRIBUTE_DELIMITERS</span> <span class="token operator">=</span> <span class="token string">",; "</span><span class="token punctuation">;</span>

<span class="token comment">/**
 * Value of a T/F attribute that represents true.
 * Anything else represents false. Case seNsItive.
 */</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">TRUE_VALUE</span> <span class="token operator">=</span> <span class="token string">"true"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">FALSE_VALUE</span> <span class="token operator">=</span> <span class="token string">"false"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">DEFAULT_VALUE</span> <span class="token operator">=</span> <span class="token string">"default"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">DESCRIPTION_ELEMENT</span> <span class="token operator">=</span> <span class="token string">"description"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">AUTOWIRE_NO_VALUE</span> <span class="token operator">=</span> <span class="token string">"no"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">AUTOWIRE_BY_NAME_VALUE</span> <span class="token operator">=</span> <span class="token string">"byName"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">AUTOWIRE_BY_TYPE_VALUE</span> <span class="token operator">=</span> <span class="token string">"byType"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">AUTOWIRE_CONSTRUCTOR_VALUE</span> <span class="token operator">=</span> <span class="token string">"constructor"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">AUTOWIRE_AUTODETECT_VALUE</span> <span class="token operator">=</span> <span class="token string">"autodetect"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">DEPENDENCY_CHECK_ALL_ATTRIBUTE_VALUE</span> <span class="token operator">=</span> <span class="token string">"all"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">DEPENDENCY_CHECK_SIMPLE_ATTRIBUTE_VALUE</span> <span class="token operator">=</span> <span class="token string">"simple"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">DEPENDENCY_CHECK_OBJECTS_ATTRIBUTE_VALUE</span> <span class="token operator">=</span> <span class="token string">"objects"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">NAME_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"name"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">BEAN_ELEMENT</span> <span class="token operator">=</span> <span class="token string">"bean"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">META_ELEMENT</span> <span class="token operator">=</span> <span class="token string">"meta"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">ID_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"id"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">PARENT_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"parent"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">CLASS_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"class"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">ABSTRACT_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"abstract"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">SCOPE_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"scope"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">SINGLETON_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"singleton"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">LAZY_INIT_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"lazy-init"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">AUTOWIRE_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"autowire"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">AUTOWIRE_CANDIDATE_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"autowire-candidate"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">PRIMARY_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"primary"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">DEPENDENCY_CHECK_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"dependency-check"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">DEPENDS_ON_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"depends-on"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">INIT_METHOD_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"init-method"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">DESTROY_METHOD_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"destroy-method"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">FACTORY_METHOD_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"factory-method"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">FACTORY_BEAN_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"factory-bean"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">CONSTRUCTOR_ARG_ELEMENT</span> <span class="token operator">=</span> <span class="token string">"constructor-arg"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">INDEX_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"index"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">TYPE_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"type"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">VALUE_TYPE_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"value-type"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">KEY_TYPE_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"key-type"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">PROPERTY_ELEMENT</span> <span class="token operator">=</span> <span class="token string">"property"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">REF_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"ref"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">VALUE_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"value"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">LOOKUP_METHOD_ELEMENT</span> <span class="token operator">=</span> <span class="token string">"lookup-method"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">REPLACED_METHOD_ELEMENT</span> <span class="token operator">=</span> <span class="token string">"replaced-method"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">REPLACER_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"replacer"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">ARG_TYPE_ELEMENT</span> <span class="token operator">=</span> <span class="token string">"arg-type"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">ARG_TYPE_MATCH_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"match"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">REF_ELEMENT</span> <span class="token operator">=</span> <span class="token string">"ref"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">IDREF_ELEMENT</span> <span class="token operator">=</span> <span class="token string">"idref"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">BEAN_REF_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"bean"</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">String</span> <span class="token constant">LOCAL_REF_ATTRIBUTE</span> <span class="token operator">=</span> <span class="token string">"local"</span><span class="token punctuation">;</span>
    
    <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>

看出来了么，主要都是 xml 里面的那些元素的名称。

里面的方法，很多，我们用到了再说。

我们继续回到主线任务：

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org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader#parseBeanDefinitions
/**
	 * 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) {
		// 一般来说，我们的根节点都是 <beans>，这个是默认 namespace 的
		if (delegate.isDefaultNamespace(root)) {
			NodeList nl = root.getChildNodes();
			// 遍历 xml <beans> 下的每个元素
			for (int i = 0; i < nl.getLength(); i++) {
				Node node = nl.item(i);
				if (node instanceof Element) {
					Element ele = (Element) node;
					// 判断元素是不是默认命名空间的，比如 <bean> 是，<context:component-scan> 不是
					if (delegate.isDefaultNamespace(ele)) {
						parseDefaultElement(ele, delegate);
					}
					else {
						//<context:component-scan>，<aop:xxxx> 走这边
						delegate.parseCustomElement(ele);
					}
				}
			}
		}
		else {
			delegate.parseCustomElement(root);
		}
	}

这里，判断一个元素是不是默认命名空间，具体怎么做的呢：

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BeanDefinitionParserDelegate#isDefaultNamespace(org.w3c.dom.Node)	
public boolean isDefaultNamespace(Node node) {
    // 调用重载方法
    return isDefaultNamespace(getNamespaceURI(node));
}

public static final String BEANS_NAMESPACE_URI = "http://www.springframework.org/schema/beans";


public boolean isDefaultNamespace(String namespaceUri) {
return (!StringUtils.hasLength(namespaceUri) || BEANS_NAMESPACE_URI.equals(namespaceUri));
}

默认 namespace 时的逻辑#

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DefaultBeanDefinitionDocumentReader#parseDefaultElement
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);
		}
	}

第一次发现，原来默认命名空间下，才这么几个元素：

import、alias、bean、（NESTED_BEANS_ELEMENT）beans

具体的解析放到下讲，这讲内容已经够多了。

非默认 namespace 时的逻辑#

主要是处理：aop、context等非默认namespace。

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BeanDefinitionParserDelegate
public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
		String namespaceUri = getNamespaceURI(ele);
         // 这里，就和前面串起来了，根据 namespace 找 handler 
		NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
		if (handler == null) {
			error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
			return null;
		}
		return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
	}

我们挑一个大家最熟悉的org.springframework.context.config.ContextNamespaceHandler，大家先看看：

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public class ContextNamespaceHandler extends NamespaceHandlerSupport {

<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">init</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token comment">// 这个也熟悉吧</span>
	<span class="token function">registerBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token string">"property-placeholder"</span><span class="token punctuation">,</span> <span class="token keyword">new</span> <span class="token class-name">PropertyPlaceholderBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token function">registerBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token string">"property-override"</span><span class="token punctuation">,</span> <span class="token keyword">new</span> <span class="token class-name">PropertyOverrideBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token function">registerBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token string">"annotation-config"</span><span class="token punctuation">,</span> <span class="token keyword">new</span> <span class="token class-name">AnnotationConfigBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token comment">// 这个熟悉吧</span>
	<span class="token function">registerBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token string">"component-scan"</span><span class="token punctuation">,</span> <span class="token keyword">new</span> <span class="token class-name">ComponentScanBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token function">registerBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token string">"load-time-weaver"</span><span class="token punctuation">,</span> <span class="token keyword">new</span> <span class="token class-name">LoadTimeWeaverBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token function">registerBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token string">"spring-configured"</span><span class="token punctuation">,</span> <span class="token keyword">new</span> <span class="token class-name">SpringConfiguredBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token function">registerBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token string">"mbean-export"</span><span class="token punctuation">,</span> <span class="token keyword">new</span> <span class="token class-name">MBeanExportBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token function">registerBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token string">"mbean-server"</span><span class="token punctuation">,</span> <span class="token keyword">new</span> <span class="token class-name">MBeanServerBeanDefinitionParser</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>



}

总之，到了这里，就是根据具体的元素，找对应的处理器了。这些都后面再说了。内容太多了。

总结#

大家可以回头再去看看第二章的整体流程，会不会清晰一些了呢？

主要是几个核心类：

XmlBeanDefinitionReader

BeanDefinitionDocumentReader

XmlReaderContext

namespaceHandlerResolver

BeanDefinitionParserDelegate

内容有点多，大家不要慌，我们后面还会进一步讲解的。觉得有帮助的话，点个赞哦。


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