web应用启动的时候SpringMVC容器加载过程

2019-05-22 06:31:20来源：博客园阅读 ()

<!-- 配置DispatcherServlet -->
    <servlet>
        <servlet-name>springmvc</servlet-name>
        <!-- DispatcherServlet类的全限定类名 -->
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <!-- DispatcherServlet类的初始化参数 -->
            <param-name>contextConfigLocation</param-name>
            <!-- 初始化参数的值，即springmvc配置文件的路径 -->
            <param-value>classpath:springmvc-config.xml</param-value>
        </init-param>
        <!-- 表示web应用启动即加载该servlet -->
        <load-on-startup>1</load-on-startup>
    </servlet>
    <!-- servlet-mapping，用于拦截所有请求。即所有请求都拦截到该sevlet -->
    <servlet-mapping>
        <servlet-name>springmvc</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

上面是在web.xml配置文件中加载springmvc配置文件生成webapplicationcontext容器的经典配置。

我们可以看到，在web应用一启动，该DispatcherServlet就被加载了，加载的时候提供了contextConfigLoacation的初始值，然后通过类的全限定类名使用反射加载该类。

/**
     * Set the context config location explicitly, instead of relying on the default
     * location built from the namespace. This location string can consist of
     * multiple locations separated by any number of commas and spaces.
     */
    public void setContextConfigLocation(String contextConfigLocation) {
        this.contextConfigLocation = contextConfigLocation;
    }

以上代码是在DispatcherSevlet父类FrameworkServlet中，可以看到提供contextConfigloaction后该类就有了srpingmvc配置文件路径。

protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
        Class<?> contextClass = getContextClass();
        if (this.logger.isDebugEnabled()) {
            this.logger.debug("Servlet with name '" + getServletName() +
                    "' will try to create custom WebApplicationContext context of class '" +
                    contextClass.getName() + "'" + ", using parent context [" + parent + "]");
        }
        if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
            throw new ApplicationContextException(
                    "Fatal initialization error in servlet with name '" + getServletName() +
                    "': custom WebApplicationContext class [" + contextClass.getName() +
                    "] is not of type ConfigurableWebApplicationContext");
        }
        ConfigurableWebApplicationContext wac =
                (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);

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

        configureAndRefreshWebApplicationContext(wac);

        return wac;
    }