---

前言

想必大家在刚开始使用SpringMVC处理静态资源的时候都遇到过问题，当DispatchServlet找不到静态资源的时候就会报404错误。然后都会被建议使用下面三种方式来处理静态资源。

1.使用Web容器的defaultServlet

<servlet-mapping>     
    <servlet-name>default</servlet-name>    
    <url-pattern>*.jpg</url-pattern>       
</servlet-mapping>      
<servlet-mapping>         
    <servlet-name>default</servlet-name>      
    <url-pattern>*.js</url-pattern>      
</servlet-mapping>      
<servlet-mapping>          
    <servlet-name>default</servlet-name>         
    <url-pattern>*.css</url-pattern>        
</servlet-mapping>      
<!-- 
放在DispatchServlet前面
-->

2.在SpringMVC配置文件中加入如下配置

<mvc:default-servlet-handler/>  

3.在SpringMVC配置文件中加入如下配置

<mvc:resources mapping="/images/**" location="/images/" />    

我们需要做的操作看起来十分简单，只需要加一行配置就行，但是你有好好的思考过为什么加上这一行就可以吗？今天我们就来探究一下其中的原理，并且顺带把SpringMVC配置文件里的要点都讲一下。所以我们就从一个已经写好的SpringMVC配置文件说起。

SpringMVC配置文件的解析

<?xml version="1.0" encoding="UTF-8"?>  
<beans xmlns="http://www.springframework.org/schema/beans"  
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"  
    xmlns:context="http://www.springframework.org/schema/context"  
    xmlns:mvc="http://www.springframework.org/schema/mvc"  
    xsi:schemaLocation="http://www.springframework.org/schema/beans    
                        http://www.springframework.org/schema/beans/spring-beans-3.1.xsd    
                        http://www.springframework.org/schema/context    
                        http://www.springframework.org/schema/context/spring-context-3.1.xsd    
                        http://www.springframework.org/schema/mvc    
                        http://www.springframework.org/schema/mvc/spring-mvc-4.0.xsd">  
    <!-- 自动扫描该包，使SpringMVC认为包下用了@controller注解的类是控制器
           <mvc:default-servlet-handler></mvc:default-servlet-handler>
        http://blog.csdn.net/cq1982/article/details/44101761
     -->  



          <context:component-scan base-package="com.ulic.gpolicyutils.controller,com.ulic.utils.createpdffield" />  



    <mvc:annotation-driven>
        <mvc:message-converters register-defaults="true">
            <!-- @ResponseBody乱码问题，将StringHttpMessageConverter的默认编码设为UTF-8 -->
            <bean class="org.springframework.http.converter.StringHttpMessageConverter">
                <constructor-arg value="UTF-8" />
            </bean>
            <!-- 配置Fastjson支持 -->
            <bean
                class="com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter">
                <property name="charset" value="UTF-8" />
                <property name="supportedMediaTypes">
                    <list>
                        <value>application/json</value>
                        <value>text/html;charset=UTF-8</value>
                    </list>
                </property>
                <property name="features">
                    <list>
                        <value>WriteMapNullValue</value>
                        <value>QuoteFieldNames</value>
                        <value>WriteDateUseDateFormat</value>
                        <value>WriteEnumUsingToString</value>
                    </list>
                </property>
            </bean>
        </mvc:message-converters>
    </mvc:annotation-driven>

<mvc:resources location="classpath:/WEB-INF/style/" mapping="/style/**"/> 
<mvc:resources location="classpath:/WEB-INF/script/" mapping="/script/**"/> 
    <!-- 定义跳转的文件的前后缀 ，视图模式配置-->  

    <!--JSP视图解析器-->
    <bean id="viewResolverJsp" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <property name="suffix" value=".jsp"/>
        <property name="viewClass" value="org.springframework.web.servlet.view.InternalResourceView"/>
        <property name="order" value="1"/>
    </bean>

    <!-- 配置freeMarker视图解析器 -->
    <bean id="viewResolverFtl" class="org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver">
        <property name="viewClass" value="org.springframework.web.servlet.view.freemarker.FreeMarkerView"/>
        <property name="contentType" value="text/html; charset=UTF-8"/>
        <property name="exposeRequestAttributes" value="true" />
        <property name="exposeSessionAttributes" value="true" />
        <property name="exposeSpringMacroHelpers" value="true" />
            <property name="requestContextAttribute" value="request" />

        <property name="cache" value="true" />

        <property name="suffix" value=".ftl" />
        <property name="order" value="0"/>
    </bean>

    <!-- 配置freeMarker的模板路径 -->
    <bean id="freemarkerConfig" class="org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer">
        <property name="templateLoaderPath" value="/WEB-INF/freemarker/"/>
        <property name="freemarkerVariables">
            <map>
                <entry key="xml_escape" value-ref="fmXmlEscape" />
            </map>
        </property>
        <property name="defaultEncoding" value="UTF-8"/>
        <property name="freemarkerSettings">
            <props>
                <prop key="template_update_delay">3600</prop>
                <prop key="locale">zh_CN</prop>
                <prop key="datetime_format">yyyy-MM-dd HH:mm:ss</prop>
                <prop key="date_format">yyyy-MM-dd</prop>
                <prop key="number_format">#.##</prop>
            </props>
        </property>
    </bean>

    <bean id="fmXmlEscape" class="freemarker.template.utility.XmlEscape"/>  
    <!-- 配置文件上传，如果没有使用文件上传可以不用配置，当然如果不配，那么配置文件中也不必引入上传组件包 -->  
    <bean id="multipartResolver"    
        class="org.springframework.web.multipart.commons.CommonsMultipartResolver">    
        <!-- 默认编码 -->  
        <property name="defaultEncoding" value="utf-8" />    
        <!-- 文件大小最大值 -->  
        <property name="maxUploadSize" value="10485760000" />    
        <!-- 内存中的最大值 -->  
        <property name="maxInMemorySize" value="40960" />    
    </bean>   

</beans>  

今天我们就要围绕着这个配置文件的解析来好好说道说道。

对于DispatchServlet的初始化，我们在之前已经讲过了，不过还有一些遗留的细节没有讲清楚。

我们今天就要接着DispatchServlet的初始化讲。

我们从他的父类FrameWorkServlet的initServletBean()说起。

@Override
    protected final void initServletBean() throws ServletException {
        getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
        if (this.logger.isInfoEnabled()) {
            this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
        }
        long startTime = System.currentTimeMillis();

        try {
            this.webApplicationContext = initWebApplicationContext();
            initFrameworkServlet();
        }
        catch (ServletException ex) {
            this.logger.error("Context initialization failed", ex);
            throw ex;
        }
        catch (RuntimeException ex) {
            this.logger.error("Context initialization failed", ex);
            throw ex;
        }

        if (this.logger.isInfoEnabled()) {
            long elapsedTime = System.currentTimeMillis() - startTime;
            this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
                    elapsedTime + " ms");
        }
    }

initServletBean里主要就是调用了initWebApplicationContext()方法，而initFrameworkServlet();在SpringMVC中并没有具体的实现，我想应该是留给我们用户自己拓展把。

initWebApplicationContext()

protected WebApplicationContext initWebApplicationContext() {
        WebApplicationContext rootContext =
                WebApplicationContextUtils.getWebApplicationContext(getServletContext());
        WebApplicationContext wac = null;

        if (this.webApplicationContext != null) {
            // A context instance was injected at construction time -> use it
            wac = this.webApplicationContext;
            if (wac instanceof ConfigurableWebApplicationContext) {
                ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
                if (!cwac.isActive()) {
                    // The context has not yet been refreshed -> provide services such as
                    // setting the parent context, setting the application context id, etc
                    if (cwac.getParent() == null) {
                        // The context instance was injected without an explicit parent -> set
                        // the root application context (if any; may be null) as the parent
                        cwac.setParent(rootContext);
                    }
                    configureAndRefreshWebApplicationContext(cwac);
                }
            }
        }
        if (wac == null) {
            // No context instance was injected at construction time -> see if one
            // has been registered in the servlet context. If one exists, it is assumed
            // that the parent context (if any) has already been set and that the
            // user has performed any initialization such as setting the context id
            wac = findWebApplicationContext();
        }
        if (wac == null) {
            // No context instance is defined for this servlet -> create a local one
            wac = createWebApplicationContext(rootContext);
        }

        if (!this.refreshEventReceived) {
            // Either the context is not a ConfigurableApplicationContext with refresh
            // support or the context injected at construction time had already been
            // refreshed -> trigger initial onRefresh manually here.
            onRefresh(wac);
        }

        if (this.publishContext) {
            // Publish the context as a servlet context attribute.
            String attrName = getServletContextAttributeName();
            getServletContext().setAttribute(attrName, wac);
            if (this.logger.isDebugEnabled()) {
                this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
                        "' as ServletContext attribute with name [" + attrName + "]");
            }
        }

        return wac;
    }

1. 获取由ContextLoaderListener初始化并注册在ServletContext中的根上下文，记为rootContext
2. 如果webApplicationContext已经不为空，表示这个Servlet类是通过编程式注册到容器中的（Servlet 3.0+中的ServletContext.addServlet() ），上下文也由编程式传入。若这个传入的上下文还没被初始化，将rootContext上下文设置为它的父上下文，然后将其初始化，否则直接使用。
3. 通过wac变量的引用是否为null，判断第2步中是否已经完成上下文的设置（即上下文是否已经用编程式方式传入），如果wac==null成立，说明该Servlet不是由编程式注册到容器中的。此时以contextAttribute属性的值为键，在ServletContext中查找上下文，查找得到，说明上下文已经以别的方式初始化并注册在contextAttribute下，直接使用。
4. 检查wac变量的引用是否为null，如果wac==null成立，说明2、3两步中的上下文初始化策略都没成功，此时调用createWebApplicationContext(rootContext)，建立一个全新的以rootContext为父上下文的上下文，作为SpringMVC配置元素的容器上下文。大多数情况下我们所使用的上下文，就是这个新建的上下文。
5. 以上三种初始化上下文的策略，都会回调onRefresh(ApplicationContext context)方法（回调的方式根据不同策略有不同），onRefresh方法在DispatcherServlet类中被覆写，以上面得到的上下文为依托，完成SpringMVC中默认实现类的初始化。
6. 最后，将这个上下文发布到ServletContext中，也就是将上下文以一个和Servlet类在web.xml中注册名字有关的值为键，设置为ServletContext的一个属性。你可以通过改变publishContext的值来决定是否发布到ServletContext中，默认为true。

FrameworkServlet类的设计目的，它是用来建立一个和Servlet关联的Spring容器上下文，并将其注册到ServletContext中的。跳脱开SpringMVC体系，我们也能通过继承FrameworkServlet类，得到与Spring容器整合的好处，FrameworkServlet和HttpServletBean一样，是一个可以独立使用的类。整个SpringMVC设计中，处处体现开闭原则，这里显然也是其中一点。

上面已经说了，在大多数情况下，我们是通过调用createWebApplicationContext(rootContext)，建立一个全新的以rootContext为父上下文的上下文。

我们就来看看createWebApplicationContext

    protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
    //XmlWebApplicationContext.class;
        Class<?> contextClass = getContextClass();

        ConfigurableWebApplicationContext wac =
                (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);

        wac.setEnvironment(getEnvironment());
        wac.setParent(parent);
        wac.setConfigLocation(getContextConfigLocation());

        configureAndRefreshWebApplicationContext(wac);

        return wac;
    }

这里面创建的子上下文是一个XmlWebApplicationContext类

    protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
    ....
        wac.refresh();
    }

注意这里调用了ApplicationContext的refresh方法，在这个方法里面就实现了Spring的IOC，也是我们这篇文章的重点。

解析和注入Bean

@Override
    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // Prepare this context for refreshing.
          //准备对上下文进行刷新，
            prepareRefresh();
            //初始化beanFactory
            // Tell the subclass to refresh the internal bean factory.
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
            // 为BeanFactory配置容器特性，例如类加载器、事件处理器等  

          //比如实现了Aware接口的Bean就会被指定执行某些方法，这个后面会讲到
            // Prepare the bean factory for use in this context.
            prepareBeanFactory(beanFactory);

            try {
                              // 为容器的某些子类指定特殊的BeanPost事件处理器  

                // Allows post-processing of the bean factory in context subclasses.
                postProcessBeanFactory(beanFactory);
                // 调用beanFactory处理器  

                // Invoke factory processors registered as beans in the context.
                invokeBeanFactoryPostProcessors(beanFactory);
                // 注册beanFactory处理器  

                // Register bean processors that intercept bean creation.
                registerBeanPostProcessors(beanFactory);
                // 初始化消息源  

                // Initialize message source for this context.
                initMessageSource();
                // 初始化上下文事件广播.  

                // Initialize event multicaster for this context.
                initApplicationEventMulticaster();
                // 初始化其它特殊bean，由子类来实现  

                // Initialize other special beans in specific context subclasses.
                onRefresh();
                // 注册事件监听器.  

                // Check for listener beans and register them.
                registerListeners();
                // 初始化所有单实例的bean，使用懒加载除外  

                // Instantiate all remaining (non-lazy-init) singletons.
                finishBeanFactoryInitialization(beanFactory);
                // 完成刷新并发布容器刷新事件  

                // Last step: publish corresponding event.
                finishRefresh();
            }

            catch (BeansException ex) {
                logger.warn("Exception encountered during context initialization - cancelling refresh attempt", ex);

                // Destroy already created singletons to avoid dangling resources.
                destroyBeans();

                // Reset 'active' flag.
                cancelRefresh(ex);

                // Propagate exception to caller.
                throw ex;
            }
        }
    }

 这个方法做了很多事情，主要有初始化beanFactory 、注册BeanFactory处理器等工作。我们接下来对里面重要的功能进行解析，它怎么读取我们配置文件并解析文件和注册配置文件里的bean。初始化beanFactory工厂时，就会读取我们配置文件并解析文件和注册配置文件里的Bean，是由AbstractApplicationContext.obtainFreshBeanFactory方法实现的

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        refreshBeanFactory();
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        if (logger.isDebugEnabled()) {
            logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
        }
        return beanFactory;
    }
    protected final void refreshBeanFactory() throws BeansException {
        if (hasBeanFactory()) {
            destroyBeans();
            closeBeanFactory();
        }
        try {
            DefaultListableBeanFactory beanFactory = createBeanFactory();
            beanFactory.setSerializationId(getId());
            customizeBeanFactory(beanFactory);
            loadBeanDefinitions(beanFactory);
            synchronized (this.beanFactoryMonitor) {
                this.beanFactory = beanFactory;
            }
        }
        catch (IOException ex) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
        }
    }

第一步：

     refreshBeanFactory 先销毁所有Bean，关闭BeanFactory，然后重新创建一个BeanFactory，并将其赋给BeanFactory实例变量。我们先看一下它怎么创建BeanFactory?     createBeanFactory这个方法是创建新的BeanBeanFactory ,而BeanFactory 的原始对象是 DefaultListableBeanFactory，这个非常关键，因为他设计到后面对这个对象的多种操作，DefaultListableBeanFactory是整个Bean加载的核心部分，是SpringMVC注册及加载Bean的默认实现。    

 第二步：先转码在读取配置文件

     loadBeanDefinitions(beanFactory) 将找到答案，这个方法将开始加载、解析 Bean 的定义，也就是把用户定义的数据结构转化为 Ioc 容器中的特定数据结构。

    @Override
    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);
    }

1.创建一个XmlBeanDefinitionReader来读取并解析XML文件，

XmlBeanDefinitionReader 是 BeanDefinitionReader 接口的实现。

 BeanDefinitionReader 读取Resource所指向的配置文件资源，然后解析配置文件，配置文件中每一个Bean解析成一个BeanDefinition对象，并保存到BeanDefinitionRegistry中。

2.为XmlBeanDefinitionReader 配置ResourceLoader等

3.

loadBeanDefinitions

    protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
        Resource[] configResources = getConfigResources();
        if (configResources != null) {
            reader.loadBeanDefinitions(configResources);
        }
      //得到configLocation，即在web.xml配置的initParam,不难理解吧，就是web.xml中配置DispatchSerlvet时指定的configLocation属性，如果没有这个属性，则默认加载classpath下*-servlet.xml
        String[] configLocations = getConfigLocations();
        if (configLocations != null) {
            reader.loadBeanDefinitions(configLocations);
        }
    }

这个方法不难理解，就是得到相关的XML配置文件，然后执行loadBeanDefinitions

//AbstractBeanDefinitionReader
@Override
    public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
        Assert.notNull(locations, "Location array must not be null");
        int counter = 0;
        for (String location : locations) {
            counter += loadBeanDefinitions(location);
        }
        return counter;
    }
@Override
    public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {
        return loadBeanDefinitions(location, null);
    }
//中间有很多跳转，能给人整懵逼，我就把每一个中间过程都放上来了
//经过一定得跳转会来到XmlBeanDefinitionReader的loadBeanDefinitions方法
@Override
    public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
        return loadBeanDefinitions(new EncodedResource(resource));
    }
    public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
        Assert.notNull(encodedResource, "EncodedResource must not be null");
        if (logger.isInfoEnabled()) {
            logger.info("Loading XML bean definitions from " + encodedResource.getResource());
        }

        Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
        if (currentResources == null) {
            currentResources = new HashSet<EncodedResource>(4);
            this.resourcesCurrentlyBeingLoaded.set(currentResources);
        }
        if (!currentResources.add(encodedResource)) {
            throw new BeanDefinitionStoreException(
                    "Detected cyclic loading of " + encodedResource + " - check your import definitions!");
        }
        try {
            InputStream inputStream = encodedResource.getResource().getInputStream();
            try {
                InputSource inputSource = new InputSource(inputStream);
                if (encodedResource.getEncoding() != null) {
                    inputSource.setEncoding(encodedResource.getEncoding());
                }
                return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
            }
            finally {
                inputStream.close();
            }
        }
        catch (IOException ex) {
            throw new BeanDefinitionStoreException(
                    "IOException parsing XML document from " + encodedResource.getResource(), ex);
        }
        finally {
            currentResources.remove(encodedResource);
            if (currentResources.isEmpty()) {
                this.resourcesCurrentlyBeingLoaded.remove();
            }
        }
    }

    /**

我们可以看到在XmlBeanDefinitionReader的 loadBeanDefinitions(Resource resource) 方法中完成了转码工作。然后调用loadBeanDefinitions(EncodedResource encodedResource)，将资源文件以流的方式读进来。

doLoadBeanDefinitions

    protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
            throws BeanDefinitionStoreException {
        try {
          //加载XML文件，并获取对应的Document。把配置文件读进来，以Document形式存储。
            Document doc = doLoadDocument(inputSource, resource);
          //解析并注册bean。
            return registerBeanDefinitions(doc, resource);
        }
    ...//省略了一堆try catch
    }
    @SuppressWarnings("deprecation")
    public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
        documentReader.setEnvironment(getEnvironment());
        int countBefore = getRegistry().getBeanDefinitionCount();
        documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
        return getRegistry().getBeanDefinitionCount() - countBefore;
    }

我们重点关注中国解析注册bean的方法

先是创建了一个DefaultBeanDefinitionDocumentReader实例

然后调用他的registerBeanDefinitions方法。

DefaultBeanDefinitionDocumentReader.registerBeanDefinitions

    @Override
    public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
        this.readerContext = readerContext;
        logger.debug("Loading bean definitions");
        Element root = doc.getDocumentElement();
        doRegisterBeanDefinitions(root);
    }
    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.
        BeanDefinitionParserDelegate parent = this.delegate;
        this.delegate = createDelegate(getReaderContext(), root, parent);

        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);
                if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
                    return;
                }
            }
        }
//空方法
        preProcessXml(root);
        parseBeanDefinitions(root, this.delegate);
        postProcessXml(root);

        this.delegate = parent;
    }

终于快到重点了。

1.创建一个BeanDefinitionParserDelegate，这是是对BeanDefinition的解析的

2.parseBeanDefinitions(root, this.delegate);把bean注册到BeanDefinition对象中

    protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
        if (delegate.isDefaultNamespace(root)) {
            NodeList nl = root.getChildNodes();
            for (int i = 0; i < nl.getLength(); i++) {
                Node node = nl.item(i);
                if (node instanceof Element) {
                    Element ele = (Element) node;
                    if (delegate.isDefaultNamespace(ele)) {
                        parseDefaultElement(ele, delegate);
                    }
                    else {
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        }
        else {
            delegate.parseCustomElement(root);
        }
    }

parseDefaultElement

    private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {   //对IMPORT标签进行处理的  
        if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
            importBeanDefinitionResource(ele);
        }
              //对ALIAS标签进行处理的  

        else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
            processAliasRegistration(ele);
        }
              //对BEAN标签进行处理的  

        else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
            processBeanDefinition(ele, delegate);
        }
        else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
            // recurse
            doRegisterBeanDefinitions(ele);
        }
    }

我们重点看一下对Bean标签的处理

processBeanDefinition

    protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
      /*
       对bean的id、name、class等属性的解析并设置到BeanDefinition然后放到放到BeanDefinitionHolder中,具体的实现可以看源码，这里不多说
      */
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if (bdHolder != null) {
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
            try {
                // Register the final decorated instance.
              //上面完成了bean的解析，这里完成注册
                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));
        }
    }
public static void registerBeanDefinition(
            BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
            throws BeanDefinitionStoreException {

        // Register bean definition under primary name.
        String beanName = definitionHolder.getBeanName();
        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

        // Register aliases for bean name, if any.
        String[] aliases = definitionHolder.getAliases();
        if (aliases != null) {
            for (String alias : aliases) {
                registry.registerAlias(beanName, alias);
            }
        }
    }

DefaultListableBeanFactory的registerBeanDefinition

//ApplicationContext也是继承BeanFactory，ApplicationContext 也继承了 ResourceLoader 接口，使得 ApplicationContext 可以访问到任何外部资源，提供了更多面向实际应用的功能

@Override
    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

        Assert.hasText(beanName, "Bean name must not be empty");
        Assert.notNull(beanDefinition, "BeanDefinition must not be null");

        if (beanDefinition instanceof AbstractBeanDefinition) {
            try {
                ((AbstractBeanDefinition) beanDefinition).validate();
            }
            catch (BeanDefinitionValidationException ex) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Validation of bean definition failed", ex);
            }
        }

        BeanDefinition oldBeanDefinition;

        oldBeanDefinition = this.beanDefinitionMap.get(beanName);
        if (oldBeanDefinition != null) {
            if (!isAllowBeanDefinitionOverriding()) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
                        "': There is already [" + oldBeanDefinition + "] bound.");
            }
            else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
                // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
                if (this.logger.isWarnEnabled()) {
                    this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
                            "' with a framework-generated bean definition: replacing [" +
                            oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            }
            else {
                if (this.logger.isInfoEnabled()) {
                    this.logger.info("Overriding bean definition for bean '" + beanName +
                            "': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            }
        }
        else {
        //*********************重点
            this.beanDefinitionNames.add(beanName);
            this.manualSingletonNames.remove(beanName);
            this.frozenBeanDefinitionNames = null;
        }
        this.beanDefinitionMap.put(beanName, beanDefinition);

        if (oldBeanDefinition != null || containsSingleton(beanName)) {
            resetBeanDefinition(beanName);
        }
    }

 先检查是不是有相同名字的BeanDefinition已经在IoC容器中注册了，如果有相同名字的BeanDefinition，但又不允许覆盖，那么会抛出异常，如果可以可以覆盖，或者IOC容器中没注册，然后把Bean的名字存入到beanDefinitionNames的同时，把beanName作为Map的key,把beanDefinition作为value存入到IoC容器持有的BeanDefinitionMap中去。直到这里就完成了Bean的注册了，但是Bean的实例化还没有进行，下面就来看一下类的实例化。

Bean的实例化

finishBeanFactoryInitialization

 首先我们先回到refresh这个方法，里面有postProcessBeanFactory这个方法，就是实例化bean的，我们带着好奇心来分析了解。当Bean定义资源被载入IoC容器之后，容器将Bean定义资源解析为容器内部的数据结构，然后BeanDefinition注册到容器中，AbstractApplicationContext类中的finishBeanFactoryInitialization方法对配置了属性的Bean进行初始化过程

然后在该方法中找到最重要的方法

preInstantiateSingletons

preInstantiateSingletons对bean进行实例化由子类DefaultListableBeanFactory来实现的

@Override
    public void preInstantiateSingletons() throws BeansException {
        if (this.logger.isDebugEnabled()) {
            this.logger.debug("Pre-instantiating singletons in " + this);
        }

        // Iterate over a copy to allow for init methods which in turn register new bean definitions.
        // While this may not be part of the regular factory bootstrap, it does otherwise work fine.
        /* （1）先List<String> beanDefinitionNames获取BeanName，然后通过BeanName 获取Map<String, RootBeanDefinition> RootBeanDefinition，然后判断是否为单例、不是抽象、是为Lazy-init=false 然后调用getBean方法。*/
        List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);

        // Trigger initialization of all non-lazy singleton beans...
        for (String beanName : beanNames) {
            RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
            if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
                if (isFactoryBean(beanName)) {
                    final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
                    boolean isEagerInit;
                    if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                        isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
                            @Override
                            public Boolean run() {
                                return ((SmartFactoryBean<?>) factory).isEagerInit();
                            }
                        }, getAccessControlContext());
                    }
                    else {
                        isEagerInit = (factory instanceof SmartFactoryBean &&
                                ((SmartFactoryBean<?>) factory).isEagerInit());
                    }
                    if (isEagerInit) {
                        getBean(beanName);
                    }
                }
                else {
                    getBean(beanName);
                }
            }
        }

        // Trigger post-initialization callback for all applicable beans...
        for (String beanName : beanNames) {
            Object singletonInstance = getSingleton(beanName);
            if (singletonInstance instanceof SmartInitializingSingleton) {
                final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
                if (System.getSecurityManager() != null) {
                    AccessController.doPrivileged(new PrivilegedAction<Object>() {
                        @Override
                        public Object run() {
                            smartSingleton.afterSingletonsInstantiated();
                            return null;
                        }
                    }, getAccessControlContext());
                }
                else {
                    smartSingleton.afterSingletonsInstantiated();
                }
            }
        }
    }

（1）先List\ beanDefinitionNames获取BeanName，然后通过BeanName 获取Map\

@Override
    public Object getBean(String name) throws BeansException {
        return doGetBean(name, null, null, false);
    }

具体的实现是由doGetBean中实现的，getBean这个方法你是不是很熟悉呢，当我们刚开始学习使用Spring的时候，我们使用了下面的方法来得到bean

ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
RegisterDAO registerDAO = (RegisterDAO)ac.getBean("RegisterDAO");

我们通过ClassPathXmlApplicationContext得到Spring上下文,然后通过getBean来得到注册到Spring容器中的Bean。那么这里的getBean其实就是我们现在看的getBean()方法。我们获取Bean都是通过这个方法来实现的。现在我们就来好好看看这个方法的具体实现。

@SuppressWarnings("unchecked")
    protected <T> T doGetBean(
            final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
            throws BeansException {
    //如果指定的是别名，将别名转换为规范的Bean名称   

        final String beanName = transformedBeanName(name);
        Object bean;
        // 如果缓存中有单例Bean时，就从缓存获取  

        // Eagerly check singleton cache for manually registered singletons.
        Object sharedInstance = getSingleton(beanName);
        if (sharedInstance != null && args == null) {
            if (logger.isDebugEnabled()) {
                if (isSingletonCurrentlyInCreation(beanName)) {
                    logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
                            "' that is not fully initialized yet - a consequence of a circular reference");
                }
                else {
                    logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
                }
            }
            bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
        }

        else {
            // Fail if we're already creating this bean instance:
            // We're assumably within a circular reference.
            if (isPrototypeCurrentlyInCreation(beanName)) {
                throw new BeanCurrentlyInCreationException(beanName);
            }

            // Check if bean definition exists in this factory.
            BeanFactory parentBeanFactory = getParentBeanFactory();
            if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
                // Not found -> check parent.
                String nameToLookup = originalBeanName(name);
                if (args != null) {
                    // Delegation to parent with explicit args.
                    return (T) parentBeanFactory.getBean(nameToLookup, args);
                }
                else {
                    // No args -> delegate to standard getBean method.
                    return parentBeanFactory.getBean(nameToLookup, requiredType);
                }
            }

            if (!typeCheckOnly) {
                markBeanAsCreated(beanName);
            }

            try {
                final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
                checkMergedBeanDefinition(mbd, beanName, args);
                // 获取当前Bean所有依赖Bean的名称  

                // Guarantee initialization of beans that the current bean depends on.
                String[] dependsOn = mbd.getDependsOn();
                if (dependsOn != null) {
                    for (String dependsOnBean : dependsOn) {
                        if (isDependent(beanName, dependsOnBean)) {
                            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                                    "Circular depends-on relationship between '" + beanName + "' and '" + dependsOnBean + "'");
                        }
                        registerDependentBean(dependsOnBean, beanName);
                                              //递归调用getBean方法  

                        getBean(dependsOnBean);
                    }
                }
                // 创建单例bean实例  

                // Create bean instance.
                if (mbd.isSingleton()) {
                                    //内部类，实现创建bean  

                    sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
                        @Override
                        public Object getObject() throws BeansException {
                            try {
                                                             //创建bean  

                                return createBean(beanName, mbd, args);
                            }
                            catch (BeansException ex) {
                                // Explicitly remove instance from singleton cache: It might have been put there
                                // eagerly by the creation process, to allow for circular reference resolution.
                                // Also remove any beans that received a temporary reference to the bean.
                                destroySingleton(beanName);
                                throw ex;
                            }
                        }
                    });
                    bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
                }
    //是否为原型bean  每次我们从容器中调用bean时，都返回一个新的实例 
                else if (mbd.isPrototype()) {
                    // It's a prototype -> create a new instance.
                    Object prototypeInstance = null;
                    try {
                        beforePrototypeCreation(beanName);
                        prototypeInstance = createBean(beanName, mbd, args);
                    }
                    finally {
                        afterPrototypeCreation(beanName);
                    }
                    bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
                }

                else {
                  //                    //创建Bean作用域类型 request、session、globalSession,通过Scope接口定义新的作用域  
//https://www.cnblogs.com/badoumi/p/5294764.html 默认的scope是singleton单例
                  /*
                  scope到底是原型还是单例，对应着有状态和无状态，而到底什么是有状态的类我们后面会专门介绍
                  */
                    String scopeName = mbd.getScope();
                    final Scope scope = this.scopes.get(scopeName);
                    if (scope == null) {
                        throw new IllegalStateException("No Scope registered for scope '" + scopeName + "'");
                    }
                    try {
                        Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
                            @Override
                            public Object getObject() throws BeansException {
                                beforePrototypeCreation(beanName);
                                try {
                                    return createBean(beanName, mbd, args);
                                }
                                finally {
                                    afterPrototypeCreation(beanName);
                                }
                            }
                        });
                        bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
                    }
                    catch (IllegalStateException ex) {
                        throw new BeanCreationException(beanName,
                                "Scope '" + scopeName + "' is not active for the current thread; " +
                                "consider defining a scoped proxy for this bean if you intend to refer to it from a singleton",
                                ex);
                    }
                }
            }
            catch (BeansException ex) {
                cleanupAfterBeanCreationFailure(beanName);
                throw ex;
            }
        }

        // Check if required type matches the type of the actual bean instance.
        if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
            try {
                return getTypeConverter().convertIfNecessary(bean, requiredType);
            }
            catch (TypeMismatchException ex) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Failed to convert bean '" + name + "' to required type [" +
                            ClassUtils.getQualifiedName(requiredType) + "]", ex);
                }
                throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
            }
        }
        return (T) bean;
    }

（2）如果BeanName是别名，先转换为原来的BeanName不是别名，然后如果缓存中有单例Bean时，就从缓存获取，如果没有的话，就创建一个

​ （3）先检查是否父工厂存在，如果有的话，获取父工厂

​ （4）判断Bean依赖对象所有的名称，如果有的话，获取依赖对象的名称，然后循环getBean（）；

​ （5）检查Bean的作用域，Scope 作用域、原型作用域、Request等，来实例化Bean ,是由FactoryBean是创建创建对象的工厂Bean，通过调用这个对象的 getObject 方法就能获取用户自定义产生的对象，从而为 Spring 提供了很好的扩展性。Spring 获取 FactoryBean 本身的对象是在前面加上 & 来完成 的。

从上述代码中，我们可以看到，真正创建Bean的方法是createBean()。

createBean()

    /**
     * Central method of this class: creates a bean instance,
     * populates the bean instance, applies post-processors, etc.
     * @see #doCreateBean
     */
    @Override
    protected Object createBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
            throws BeanCreationException {

        if (logger.isDebugEnabled()) {
            logger.debug("Creating instance of bean '" + beanName + "'");
        }
        // Make sure bean class is actually resolved at this point.
        resolveBeanClass(mbd, beanName);

        // Prepare method overrides.
        try {
            mbd.prepareMethodOverrides();
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanDefinitionStoreException(mbd.getResourceDescription(),
                    beanName, "Validation of method overrides failed", ex);
        }

        try {
            // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
            Object bean = resolveBeforeInstantiation(beanName, mbd);
            if (bean != null) {
                return bean;
            }
        }
        catch (Throwable ex) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                    "BeanPostProcessor before instantiation of bean failed", ex);
        }

        Object beanInstance = doCreateBean(beanName, mbd, args);
        if (logger.isDebugEnabled()) {
            logger.debug("Finished creating instance of bean '" + beanName + "'");
        }
        return beanInstance;
    }

doCreateBean

    /*
     * Actually create the specified bean. Pre-creation processing has already happened
     * at this point, e.g. checking {@code postProcessBeforeInstantiation} callbacks.
     * <p>Differentiates between default bean instantiation, use of a
     * factory method, and autowiring a constructor.
    */

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
        // Instantiate the bean.
      // 封装bean对象  

        BeanWrapper instanceWrapper = null;
                 //是否为单实例  

        if (mbd.isSingleton()) {
                          //根据beanName从容器中获取  

            instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
        }
        if (instanceWrapper == null) {
                           //创建  

            instanceWrapper = createBeanInstance(beanName, mbd, args);
        }
                  //获取bean的实例化  

        final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
                 //bean的类型  

        Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);

        // Allow post-processors to modify the merged bean definition.
        synchronized (mbd.postProcessingLock) {
            if (!mbd.postProcessed) {
                applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
                mbd.postProcessed = true;
            }
        }

        // Eagerly cache singletons to be able to resolve circular references
        // even when triggered by lifecycle interfaces like BeanFactoryAware.
        boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
                isSingletonCurrentlyInCreation(beanName));
        if (earlySingletonExposure) {
            if (logger.isDebugEnabled()) {
                logger.debug("Eagerly caching bean '" + beanName +
                        "' to allow for resolving potential circular references");
            }
                            //向容器中缓存单态实例的Bean对象，以防循环实例化   

            addSingletonFactory(beanName, new ObjectFactory<Object>() {
                @Override
                public Object getObject() throws BeansException {
                    return getEarlyBeanReference(beanName, mbd, bean);
                }
            });
        }

        // Initialize the bean instance.
        Object exposedObject = bean;
        try {
           //设置bean实例的属性,如果属性需要注入的bean实例，则把bean实例对象封装好依赖注入  
            populateBean(beanName, mbd, instanceWrapper);
            if (exposedObject != null) {
                                  //初始化bean  

                exposedObject = initializeBean(beanName, exposedObject, mbd);
            }
        }
        catch (Throwable ex) {
            if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
                throw (BeanCreationException) ex;
            }
            else {
                throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
            }
        }

        if (earlySingletonExposure) {
                              //获取实例化好的单态实例的bean  

            Object earlySingletonReference = getSingleton(beanName, false);
            if (earlySingletonReference != null) {
                if (exposedObject == bean) {
                    exposedObject = earlySingletonReference;
                }
                else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
                    String[] dependentBeans = getDependentBeans(beanName);
                    Set<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length);
                    for (String dependentBean : dependentBeans) {
                        if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
                            actualDependentBeans.add(dependentBean);
                        }
                    }
                    if (!actualDependentBeans.isEmpty()) {
                        throw new BeanCurrentlyInCreationException(beanName,
                                "Bean with name '" + beanName + "' has been injected into other beans [" +
                                StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
                                "] in its raw version as part of a circular reference, but has eventually been " +
                                "wrapped. This means that said other beans do not use the final version of the " +
                                "bean. This is often the result of over-eager type matching - consider using " +
                                "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
                    }
                }
            }
        }

        // Register bean as disposable.
        try {
            registerDisposableBeanIfNecessary(beanName, bean, mbd);
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
        }

        return exposedObject;
    }

这个方法并不难理解：

1.查看缓存工厂中是否已经实例化了这个Bean，如果没有找到，则创建一个新的Bean，注意，返回的是一个BeanWarpper对象,将实例对象包装起来了。

2从BeanWarpper中得到Bean

3将实例化后的Bean存入到缓存工厂中

4.实例化属性

5.返回实例Bean

注意这里有吧Bean缓存到工厂中，所以，当我们在Spring初始化之后可以通过getBean直接拿到Bean实例，而懒加载的，则会将getBean流程完整的走一遍然后获得Bean。

到这里就把注册Bean，实例化Bean讲解完了，还有许多的细节没有讲，这些留到以后再补充吧。