DispatcherServlet和ContextLoaderListener是什么？

20180509 check

接收到HTTP请求后，DispatcherServlet 询问HandlerMapping (configuration files) 去请求合适的Controller。Controller接受请求后，调用合适的service方法，然后set model data，接下来返回视图（view）给DispatcherServlet。DispatcherServlet从ViewResolver 选择定义好的视图给request请求。一旦视图确定下来，DispatcherServlet 传递model data给最终渲染到浏览器上的视图。

<web-app>
  <display-name>Archetype Created Web Application</display-name>
   
  <servlet>
        <servlet-name>spring</servlet-name>
            <servlet-class>
                org.springframework.web.servlet.DispatcherServlet
            </servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
 
    <servlet-mapping>
        <servlet-name>spring</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
     
</web-app>

ContextLoaderListener 读取spring配置文件（“contextConfigLocation” in web.xml），解析它、加载定义在配置文件中的beans。

<servlet>
        <servlet-name>spring</servlet-name>
        <servlet-class>
            org.springframework.web.servlet.DispatcherServlet
        </servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>
                WEB-INF/spring-dao-hibernate.xml,
                WEB-INF/spring-services.xml,
                WEB-INF/spring-security.xml
            </param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
 
    <servlet-mapping>
        <servlet-name>spring</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

 注：也可以将多个context files放到一个已经存在的配置文件中

<beans>
    <import resource="spring-dao-hibernate.xml"/>
    <import resource="spring-services.xml"/>
    <import resource="spring-security.xml"/>
     
    ... //Other configuration stuff
 
</beans>

<context:annotation-config> = Scanning and activating annotations in “already registered beans”.

<context:component-scan> = Bean Registration + Scanning and activating annotations