SpringMVC處理流程

在詳解SpringMVC處理流程之前渣淤，首先我們要做好準備工作，比如初始化SpringMVC容器吉嫩，如果SpringMVC和SpringMVC集成話价认，同樣也需要初始化Spring容器。

容器初始化

web.xml

<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath*:applicationContext-*.xml</param-value>
</context-param>

<servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath*:dispatcher-servlet.xml</param-value>
    </init-param>
    <load-on-startup>0</load-on-startup>
</servlet>

<servlet-mapping>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>/</url-pattern>
</servlet-mapping>

從web.xml中可以看出通過ContextLoaderListener初始化Spring容器自娩，通過DispatcherServlet初始化SpringMVC容器用踩，SpringMVC容器作為Spring容器的子容器設(shè)置在Spring容器。

ContextLoaderListener的作用

初始ApplicationContext（默認的是XmlWebApplicationContext）然后將其放在ServletContext中。

    this.context = createWebApplicationContext(servletContext, parent);
    servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
    currentContextPerThread.put(Thread.currentThread().getContextClassLoader(), this.context);

ServletContext作用

每一個web應(yīng)用都有一個 ServletContext與之相關(guān)聯(lián)捶箱。
ServletContext對象在應(yīng)用啟動的被創(chuàng)建智什，在應(yīng)用關(guān)閉的時候被銷毀。
ServletContext在全局范圍內(nèi)有效丁屎，類似于應(yīng)用中的一個全局變量荠锭。

DispatcherServlet作用

DispatcherServlet類圖

通過類圖可以看出，DispatcherServlet繼承了FrameworkServlet和HttpServletBean晨川。

HttpServletBean作用

HttpServletBean的作用主要是做一些初始化证九，將web.xml中配置的參數(shù)設(shè)置到Servlet中

//比如初始化init-param中的參數(shù)
<init-param> <param-name>contextConfigLocation</param-name> <param-value>classpath*:dispatcher-servlet.xml</param-value> </init-param>

//源碼片段
HttpServletBean.ServletConfigPropertyValues ex = new HttpServletBean.ServletConfigPropertyValues(this.getServletConfig(), this.requiredProperties);
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ServletContextResourceLoader resourceLoader = new ServletContextResourceLoader(this.getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, this.getEnvironment()));
this.initBeanWrapper(bw);
bw.setPropertyValues(ex, true);

FrameworkServlet作用

FrameworkServlet的作用講Servlet和Spring容器關(guān)聯(lián)。其實也就是初始化FrameworkServlet的屬性webApplicationContext共虑，這個屬性代表SpringMVC上下文愧怜，它有個父類上下文，既web.xml中配置的ContextLoaderListener監(jiān)聽器初始化的容器上下文妈拌。

//源碼片段
protected WebApplicationContext initWebApplicationContext() {
 //這個設(shè)置springMVC的父類上下文為ContextLoaderListener初始化的容器上下文
        WebApplicationContext rootContext = WebApplicationContextUtils.getWebApplicationContext(this.getServletContext());
        WebApplicationContext wac = null;
        if(this.webApplicationContext != null) {
            wac = this.webApplicationContext;
            if(wac instanceof ConfigurableWebApplicationContext) {
                ConfigurableWebApplicationContext attrName = (ConfigurableWebApplicationContext)wac;
                if(!attrName.isActive()) {
                    if(attrName.getParent() == null) {
                        attrName.setParent(rootContext);
                    }
                    this.configureAndRefreshWebApplicationContext(attrName);
                }
            }
        }
        if(wac == null) {
            wac = this.findWebApplicationContext();//一般返回的都是null
            //具體實現(xiàn)拥坛，獲取DispatcherServlet的applicationContext
            //WebApplicationContext wac = WebApplicationContextUtils.getWebApplicationContext(this.getServletContext(), attrName);
        }
        if(wac == null) {
            wac = this.createWebApplicationContext(rootContext);
        }
        if(!this.refreshEventReceived) {
            this.onRefresh(wac);
        }
        if(this.publishContext) {
            //attrName1=org.springframework.web.servlet.FrameworkServlet.CONTEXT.dispatcher
            String attrName1 = this.getServletContextAttributeName();
            //新創(chuàng)建的容器上下文設(shè)置到ServletContext中
            this.getServletContext().setAttribute(attrName1, wac);
            if(this.logger.isDebugEnabled()) {
                this.logger.debug("Published WebApplicationContext of servlet \'" + this.getServletName() + "\' as ServletContext attribute with name [" + attrName1 + "]");
            }
        }
        return wac;
    }

DispatcherServlet主要組建

DispatcherServlet覆寫了FrameworkServlet中的onRefresh()方法，onRefresh()方法是鉤子方法尘分，子類可以重寫自己特有的方法猜惋。

//初始化DispatcherServlet使用的策略
protected void initStrategies(ApplicationContext context) {
    this.initMultipartResolver(context);
    this.initLocaleResolver(context);
    this.initThemeResolver(context);
    this.initHandlerMappings(context);
    this.initHandlerAdapters(context);
    this.initHandlerExceptionResolvers(context);
    this.initRequestToViewNameTranslator(context);
    this.initViewResolvers(context);
    this.initFlashMapManager(context);
}