Spring 源码解析之DispatcherServlet源码解析

Posted 2020-07-19 夜宿山寺

Spring 源码解析之DispatcherServlet源码解析(五)

前言

本文需要有前四篇文章的基础，才能够清晰易懂，有兴趣可以先看看详细的流程，这篇文章可以说是第一篇文章，也可以说是前四篇文章的的汇总，Spring的整个请求流程都是围绕着DispatcherServlet进行的

类结构图

根据类的结构来说DispatcherServlet本身也是继承了HttpServlet的，所有的请求都是根据这一个Servlet来进行转发的,同时解释了为什么需要在web.xml进行如下配置，因为Spring是基于一个Servlet来展开的，当然不需要Servlet也能够使用Spring

<servlet>  
    <servlet-name>appServlet</servlet-name>  
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>  
    <init-param>  
        <param-name>contextConfigLocation</param-name>  
        <param-value>classpath:spring/spring-servlet.xml</param-value>  
    </init-param>  
    <load-on-startup>1</load-on-startup>  
</servlet>  
<servlet-mapping>  
    <servlet-name>appServlet</servlet-name>  
    <url-pattern>/</url-pattern>  
</servlet-mapping>  

1 DispatcherServlet初始化

1.1 DispatcherServlet初始化加载的几个bean

protected void initStrategies(ApplicationContext context) {
    //初始化文件上传处理类
        initMultipartResolver(context);
    //初始化本地化Resolver
        initLocaleResolver(context);
    //初始化主题Resolver
        initThemeResolver(context);
    //初始化一些个与处理的HandlerMappings
        initHandlerMappings(context);
    //
        initHandlerAdapters(context);
    //初始化异常处理的handler
        initHandlerExceptionResolvers(context);
    //初始化请求路径转换为ViewName 的Translator
        initRequestToViewNameTranslator(context);
  //初始化ViewResolvers 这个就是针对视图处理的Resolvers 比如jsp处理Resolvers 或者freemarker处理Resolvers
        initViewResolvers(context);
    //初始化 主要管理flashmap，比如RedirectAttributes 的属性会放到这个里面，默认使用的是SessionFlashMapManager
        initFlashMapManager(context);
    }

1.2 初始化流程图

1.2.1 HttpServletBean源码解析

HttpServletBean本身来说是一个普通的servlet而已,主要做一些资源的初始化

public abstract class HttpServletBean extends HttpServlet
        implements EnvironmentCapable, EnvironmentAware {

    protected final Log logger = LogFactory.getLog(getClass());

    /**
     * Set of required properties (Strings) that must be supplied as
     * config parameters to this servlet.
     */
    private final Set<String> requiredProperties = new HashSet<String>();

    private ConfigurableEnvironment environment;


    /**
     * Subclasses can invoke this method to specify that this property
     * (which must match a JavaBean property they expose) is mandatory,
     * and must be supplied as a config parameter. This should be called
     * from the constructor of a subclass.
     * <p>This method is only relevant in case of traditional initialization
     * driven by a ServletConfig instance.
     * @param property name of the required property
     */
    protected final void addRequiredProperty(String property) {
        this.requiredProperties.add(property);
    }

    /**
     * Map config parameters onto bean properties of this servlet, and
     * invoke subclass initialization.
     * @throws ServletException if bean properties are invalid (or required
     * properties are missing), or if subclass initialization fails.
     */
    @Override
    public final void init() throws ServletException {
        if (logger.isDebugEnabled()) {
            logger.debug("Initializing servlet ‘" + getServletName() + "‘");
        }

        // Set bean properties from init parameters.
        try {
      //使用Servlet配置的初始化参数创建一个PropertyValues对象,PropertyValues对象是名值对的集合, 子类也可以指定哪些属性是必须的  
            PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
      //把当前的Servlet当作一个Bean, 把Bean的属性以及属性的存取方法信息放入BeanWrapper对象  
            BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
      //注册一个可以在资源和路径之间进行转化的客户化编辑器，这些资源是这个Web应用的内部资源，例如，一个文件，一个图片等等  
            ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
            bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
       //提供给子类机会增加更多的客户化的编辑器，或者对BeanWrapper进行更多的初始化  
            initBeanWrapper(bw);
      //把初始化制定的参数值赋值到Servlet的属性中，第二个参数true表明忽略位置属性  
            bw.setPropertyValues(pvs, true);
        }
        catch (BeansException ex) {
            logger.error("Failed to set bean properties on servlet ‘" + getServletName() + "‘", ex);
            throw ex;
        }

        // Let subclasses do whatever initialization they like.
    //提供给子类的的初始化方法 目前是FrameworkServlet 进行了实现
        initServletBean();

        if (logger.isDebugEnabled()) {
            logger.debug("Servlet ‘" + getServletName() + "‘ configured successfully");
        }
    }

    /**
     * Initialize the BeanWrapper for this HttpServletBean,
     * possibly with custom editors.
     * <p>This default implementation is empty.
     * @param bw the BeanWrapper to initialize
     * @throws BeansException if thrown by BeanWrapper methods
     * @see org.springframework.beans.BeanWrapper#registerCustomEditor
     */
    protected void initBeanWrapper(BeanWrapper bw) throws BeansException {
    }


    /**
     * Overridden method that simply returns {@code null} when no
     * ServletConfig set yet.
     * @see #getServletConfig()
     */
    @Override
    public final String getServletName() {
        return (getServletConfig() != null ? getServletConfig().getServletName() : null);
    }

    /**
     * Overridden method that simply returns {@code null} when no
     * ServletConfig set yet.
     * @see #getServletConfig()
     */
    @Override
    public final ServletContext getServletContext() {
        return (getServletConfig() != null ? getServletConfig().getServletContext() : null);
    }


    /**
     * Subclasses may override this to perform custom initialization.
     * All bean properties of this servlet will have been set before this
     * method is invoked.
     * <p>This default implementation is empty.
     * @throws ServletException if subclass initialization fails
     */
    protected void initServletBean() throws ServletException {
    }

    /**
     * {@inheritDoc}
     * @throws IllegalArgumentException if environment is not assignable to
     * {@code ConfigurableEnvironment}.
     */
    @Override
    public void setEnvironment(Environment environment) {
        Assert.isInstanceOf(ConfigurableEnvironment.class, environment);
        this.environment = (ConfigurableEnvironment) environment;
    }

    /**
     * {@inheritDoc}
     * <p>If {@code null}, a new environment will be initialized via
     * {@link #createEnvironment()}.
     */
    @Override
    public ConfigurableEnvironment getEnvironment() {
        if (this.environment == null) {
            this.environment = this.createEnvironment();
        }
        return this.environment;
    }

    /**
     * Create and return a new {@link StandardServletEnvironment}. Subclasses may override
     * in order to configure the environment or specialize the environment type returned.
     */
    protected ConfigurableEnvironment createEnvironment() {
        return new StandardServletEnvironment();
    }


    /**
     * PropertyValues implementation created from ServletConfig init parameters.
     */
   //主要是用来添加初始化参数的
    private static class ServletConfigPropertyValues extends MutablePropertyValues {

        /**
         * Create new ServletConfigPropertyValues.
         * @param config ServletConfig we‘ll use to take PropertyValues from
         * @param requiredProperties set of property names we need, where
         * we can‘t accept default values requiredProperties 这个参数主要是指定初始化时必须添加的参数
         * @throws ServletException if any required properties are missing
         */
        public ServletConfigPropertyValues(ServletConfig config, Set<String> requiredProperties)
            throws ServletException {

            Set<String> missingProps = (requiredProperties != null && !requiredProperties.isEmpty()) ?
                    new HashSet<String>(requiredProperties) : null;

            Enumeration<String> en = config.getInitParameterNames();
            while (en.hasMoreElements()) {
                String property = en.nextElement();
                Object value = config.getInitParameter(property);
                addPropertyValue(new PropertyValue(property, value));
                if (missingProps != null) {
                    missingProps.remove(property);
                }
            }

            // Fail if we are still missing properties.
            if (missingProps != null && missingProps.size() > 0) {
                throw new ServletException(
                    "Initialization from ServletConfig for servlet ‘" + config.getServletName() +
                    "‘ failed; the following required properties were missing: " +
                    StringUtils.collectionToDelimitedString(missingProps, ", "));
            }
        }
    }

}

1.2.1 FrameworkServlet源码解析

这里只贴初始化的需要的部分代码，根据上面的逻辑，子类实现了initServletBean()这个方法进行初始化

public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {

    protected void initFrameworkServlet() throws ServletException {
    }
    //实现HttpServletBean 的初始化接口
    @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 {
        //初始化webApplicationContext
            this.webApplicationContext = initWebApplicationContext();
        //这个是留给子类去实现的方法，暂时来说没有具体的实现，主要是留给开发人员自定义一些特性的时候
        //这个时候WebApplicationContext已经被初始化了，也就是一些个spring的配置文件已经被初始化了
            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");
        }
    }

    protected WebApplicationContext initWebApplicationContext() {
    //获取根的Context对象，比如说我用了Spring boot或者注解的方式进行初始化，那么这里的Context就是Spring boot或者其他的context对象
        WebApplicationContext rootContext =
                WebApplicationContextUtils.getWebApplicationContext(getServletContext());
        WebApplicationContext wac = null;
    //如果当前的webApplicationContext 不等于null
        if (this.webApplicationContext != null) {
            // A context instance was injected at construction time -> use it
            wac = this.webApplicationContext;
      //如果context对象是ConfigurableWebApplicationContext
            if (wac instanceof ConfigurableWebApplicationContext) {
                ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
        //如果ConfigurableWebApplicationContext 不是存活状态
                if (!cwac.isActive()) {
                    // The context has not yet been refreshed -> provide services such as
                    // setting the parent context, setting the application context id, etc
          //如果没有设置过parent
                    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
      //查询当前的Context，下述有详细讲解
            wac = findWebApplicationContext();
        }
    //如果没有找到那么就通过rootContext 去创建一个Context对象
        if (wac == null) {
            // No context instance is defined for this servlet -> create a local one
            wac = createWebApplicationContext(rootContext);
        }
    //如果允许通过事件通知，那么就直接初始化。通过事件的通知可以反向的说明onRefresh()这个方法是可以被重复调用的，具体分析看下面
        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);
        }
    // Publish the context as a servlet context attribute.
  //如果允许publish Context的话那么就把spring context放入到spring的ServletContext中
        if (this.publishContext) {
            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;
    }
  //创建and refresh WebApplicationContext
  protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
    //判断id
        if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
            // The application context id is still set to its original default value
            // -> assign a more useful id based on available information
            if (this.contextId != null) {
                wac.setId(this.contextId);
            }
            else {
                // Generate default id...
                wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
                        ObjectUtils.getDisplayString(getServletContext().getContextPath()) + "/" + getServletName());
            }
        }

        wac.setServletContext(getServletContext());
        wac.setServletConfig(getServletConfig());
        wac.setNamespace(getNamespace());
    //添加针对ContextRefreshListener事件的监听
    //ApplicationListener decorator that filters events from a specified event source, invoking its delegate listener for matching ApplicationEvent objects only.
    //看了一下英文，大概是用了decorator（装饰）模式，具体源码里面，也只是做了一个简单的装饰模式，这个类接受所有的ApplicationEvent事件
        wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));

        // The wac environment‘s #initPropertySources will be called in any case when the context
        // is refreshed; do it eagerly here to ensure servlet property sources are in place for
        // use in any post-processing or initialization that occurs below prior to #refresh
        ConfigurableEnvironment env = wac.getEnvironment();
        if (env instanceof ConfigurableWebEnvironment) {
            ((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());
        }
    //Post-process the given WebApplicationContext before it is refreshed
    //大概就是说，在初始化handlermapping和一些本地化等调用refresh方法之前处理WebApplicationContext，这个类没有具体实现，开发者可以自己去处理
        postProcessWebApplicationContext(wac);
    //spring dispatcherServlet初始化的时候可以指定初始化一些类
        applyInitializers(wac);
    //这个是重点方法，这里采用了事件的模式进行通知，去调用refresh方法初始化配置
        wac.refresh();
    }
  //初始化spring context的时候 初始化一些指定需要初始化的类 这些类需要实现ApplicationContextInitializer 这个接口才能进行调用
  protected void applyInitializers(ConfigurableApplicationContext wac) {
    //获取到ServletContext中初始化的类数组参数
    //
        String globalClassNames = getServletContext().getInitParameter(ContextLoader.GLOBAL_INITIALIZER_CLASSES_PARAM);
        if (globalClassNames != null) {
      //不断的去初始化这个类数组 以,;\t\n等作为分隔符
            for (String className : StringUtils.tokenizeToStringArray(globalClassNames, INIT_PARAM_DELIMITERS)) {
                this.contextInitializers.add(loadInitializer(className, wac));
            }
        }

        if (this.contextInitializerClasses != null) {
            for (String className : StringUtils.tokenizeToStringArray(this.contextInitializerClasses, INIT_PARAM_DELIMITERS)) {
                this.contextInitializers.add(loadInitializer(className, wac));
            }
        }
    //排序，可以指定这些类的初始化顺序，通过@Order注解来实现排序
        AnnotationAwareOrderComparator.sort(this.contextInitializers);
    //初始化
        for (ApplicationContextInitializer<ConfigurableApplicationContext> initializer : this.contextInitializers) {
            initializer.initialize(wac);
        }
    }
  //初始化类，
  private ApplicationContextInitializer<ConfigurableApplicationContext> loadInitializer(
            String className, ConfigurableApplicationContext wac) {
        try {
      //加载这个类
            Class<?> initializerClass = ClassUtils.forName(className, wac.getClassLoader());
      //判断是否实现了接口ApplicationContextInitializer
            Class<?> initializerContextClass =
                    GenericTypeResolver.resolveTypeArgument(initializerClass, ApplicationContextInitializer.class);
            if (initializerContextClass != null && !initializerContextClass.isInstance(wac)) {
                throw new ApplicationContextException(String.format(
                        "Could not apply context initializer [%s] since its generic parameter [%s] " +
                        "is not assignable from the type of application context used by this " +
                        "framework servlet: [%s]", initializerClass.getName(), initializerContextClass.getName(),
                        wac.getClass().getName()));
            }
      //初始化对象
            return BeanUtils.instantiateClass(initializerClass, ApplicationContextInitializer.class);
        }
        catch (ClassNotFoundException ex) {
            throw new ApplicationContextException(String.format("Could not load class [%s] specified " +
                    "via ‘contextInitializerClasses‘ init-param", className), ex);
        }
    }
}

上述代码获取root Context的时候可以通过如下代码了解到获取方式，webapp的Context对象的保存，其实无非就是把spring的context放到了ServletContext的一个属性中而已

WebApplicationContext rootContext =
    WebApplicationContextUtils.getWebApplicationContext(getServletContext());

public abstract class WebApplicationContextUtils {
  public static WebApplicationContext getWebApplicationContext(ServletContext sc) {
        return getWebApplicationContext(sc, WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
    }

    /**
     * Find a custom {@code WebApplicationContext} for this web app.
     * @param sc ServletContext to find the web application context for
     * @param attrName the name of the ServletContext attribute to look for
     * @return the desired WebApplicationContext for this web app, or {@code null} if none
     */
    public static WebApplicationContext getWebApplicationContext(ServletContext sc, String attrName) {
        Assert.notNull(sc, "ServletContext must not be null");
    //通过从ServletContext 去获取spring的context对象
        Object attr = sc.getAttribute(attrName);
        if (attr == null) {
            return null;
        }
        if (attr instanceof RuntimeException) {
            throw (RuntimeException) attr;
        }
        if (attr instanceof Error) {
            throw (Error) attr;
        }
        if (attr instanceof Exception) {
            throw new IllegalStateException((Exception) attr);
        }
        if (!(attr instanceof WebApplicationContext)) {
            throw new IllegalStateException("Context attribute is not of type WebApplicationContext: " + attr);
        }
        return (WebApplicationContext) attr;
    }
}

wac = findWebApplicationContext(); 上述这块逻辑主要是通过获取ContextAttribute的属性名去ServletContext中获取Context对象

protected WebApplicationContext findWebApplicationContext() {
    String attrName = getContextAttribute();
    if (attrName == null) {
      return null;
    }
    WebApplicationContext wac =
        WebApplicationContextUtils.getWebApplicationContext(getServletContext(), attrName);
    if (wac == null) {
      throw new IllegalStateException("No WebApplicationContext found: initializer not registered?");
    }
    return wac;
}

1.2.2 FrameworkServlet 中refresh源码解析

这里流程比较繁琐，重点讲述一下 wac.refresh(); 这个方法会调用AbstractApplicationContext这里类面的refresh去实现相应的逻辑，这个类具体的英文解释（implements common context functionality. Uses the Template Method design pattern） 大概意思就是说实现了一些公有的方法，通过Template Method这种设计模式实现功能，其实也就是将逻辑放到了AbstractApplicationContext中，然后子类去实现各种方法。逻辑已经由AbstractApplicationContext定好，子类不关心逻辑

public abstract class AbstractApplicationContext extends DefaultResourceLoader
        implements ConfigurableApplicationContext, DisposableBean {
  //准备刷新之前调用    
  protected void prepareRefresh() {
    //记录开始时间
        this.startupDate = System.currentTimeMillis();
    //改变状态
        this.closed.set(false);
        this.active.set(true);

        if (logger.isInfoEnabled()) {
            logger.info("Refreshing " + this);
        }

        // Initialize any placeholder property sources in the context environment
    //这个主要留给子类去实现
        initPropertySources();

        // Validate that all properties marked as required are resolvable
        // see ConfigurablePropertyResolver#setRequiredProperties
    //校验必须初始化的参数
        getEnvironment().validateRequiredProperties();

        // Allow for the collection of early ApplicationEvents,
        // to be published once the multicaster is available...
        this.earlyApplicationEvents = new LinkedHashSet<ApplicationEvent>();
    }
  //初始化一些beanFactory参数
  protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        // Tell the internal bean factory to use the context‘s class loader etc.
    //设置classLoader
        beanFactory.setBeanClassLoader(getClassLoader());
    //设置bean表达式解析器 spring 的el 表达式
        beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
    //使用资源编辑器来填充指定的PropertyEditorRegistry。
        beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

        // Configure the bean factory with context callbacks.
    //负责注入ResourceLoaderAware, ApplicationEventPublisherAware, MessageSourceAware, ApplicationContextAware ApplicationContext相关特性的Bean
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
        beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
        beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
        beanFactory.ignoreDependencyInterface(EnvironmentAware.class);

        // BeanFactory interface not registered as resolvable type in a plain factory.
        // MessageSource registered (and found for autowiring) as a bean.
    //This is intended for factory/context references that are supposed to be autowirable but are not defined as beans in the factory: e.g. a dependency of type ApplicationContext resolved to the ApplicationContext instance that the bean is living in.
    //上述英文大概意思就是定义了一个特殊的bean，但是这个bean不通过 beanFactory进行管理生命周期，beanFactory本身就是一个bean，自身管理自身就有点奇怪，所以这个方法是注册一些特殊的bean，并且可以进行注入
        beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
        beanFactory.registerResolvableDependency(ResourceLoader.class, this);
        beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
        beanFactory.registerResolvableDependency(ApplicationContext.class, this);

        // Detect a LoadTimeWeaver and prepare for weaving, if found.
        if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            // Set a temporary ClassLoader for type matching.
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }

        // Register default environment beans.
        if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
        }
        if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
        }
        if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
        }
    }

  @Override
    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // Prepare this context for refreshing.
      //preparecontext之前执行的操作
            prepareRefresh();
      //告诉子类刷新bean工厂，spring boot能够做到改变一个类进行热部署，我猜可能就调用了这个刷新方法去刷新bean工厂，所以改变了一些静态变量spring boot是不会动态刷新的
            // Tell the subclass to refresh the internal bean factory.
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // Prepare the bean factory for use in this context.
      //初始化一些bean工厂的参数
            prepareBeanFactory(beanFactory);

            try {
                // Allows post-processing of the bean factory in context subclasses.
        // 增加处理servletContext的类
                postProcessBeanFactory(beanFactory);

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

                // Register bean processors that intercept bean creation.
                registerBeanPostProcessors(beanFactory);
        //初始化消息源
                // Initialize message source for this context.
                initMessageSource();
        //初始化消息事件
                // Initialize event multicaster for this context.
                initApplicationEventMulticaster();

                // Initialize other special beans in specific context subclasses.
                onRefresh();

                // Check for listener beans and register them.
                registerListeners();

                // Instantiate all remaining (non-lazy-init) singletons.
                finishBeanFactoryInitialization(beanFactory);
        //发送refresh事件
                // Last step: publish corresponding event.
                finishRefresh();
            }

            catch (BeansException ex) {
                if (logger.isWarnEnabled()) {
                    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;
            }

            finally {
                // Reset common introspection caches in Spring‘s core, since we
                // might not ever need metadata for singleton beans anymore...
                resetCommonCaches();
            }
        }
    }
}

AbstractApplicationContext这个类比较繁琐，这里只大概描述了一下大概的功能，后续文章会详细进行讲解，这里主要是讲解初始化流程

Spring 总体流程图

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