关于ssm项目整合中web.xml配置的问题

最近在回顾ssm项目整合的过程中，遇到了浏览器访问出现404的问题，仔细检查了所有配置，没有问题，于是检查web.xml发现问题，为什么配置spring mvc的前端控制器要有引用applicationContext.xml，而不是springmvc-config.xml。于是百度了一下，说web.xml需要配置spring监听器，跟spring mvc的前端控制器是分开配置的，按照百度的改过来之后可以正常访问。
我的web.xml配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">

    <!--配置DispatcherServlet-->
    <servlet>
        <servlet-name>spring-dispatcher</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:applicationContext.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>spring-dispatcher</servlet-name>
        <!--默认匹配所有请求-->
        <url-pattern>/</url-pattern>
    </servlet-mapping>

    <!--乱码过滤-->
    <filter>
        <filter-name>characterEncoding</filter-name>
        <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
        <init-param>
            <param-name>encoding</param-name>
            <param-value>utf-8</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>characterEncoding</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

    <!--session过期时间-->
    <session-config>
        <session-timeout>15</session-timeout>
    </session-config>

</web-app>

配置DispatcherServlet处引用的是applicationContext.xml，这样是会报404。改了之后的web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">

    <!--配置监听器-->
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:applicationContext.xml</param-value>
    </context-param>
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

    <!--配置DispatcherServlet-->
    <servlet>
        <servlet-name>spring-dispatcher</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc-config.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>spring-dispatcher</servlet-name>
        <!--默认匹配所有请求-->
        <url-pattern>/</url-pattern>
    </servlet-mapping>

    <!--乱码过滤-->
    <filter>
        <filter-name>characterEncoding</filter-name>
        <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
        <init-param>
            <param-name>encoding</param-name>
            <param-value>utf-8</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>characterEncoding</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

    <!--session过期时间-->
    <session-config>
        <session-timeout>15</session-timeout>
    </session-config>

</web-app>

配置了监听器，引用的是applicationContext.xml，而配置DispatcherServlet处引用改成了springmvc-config.xml,这样就能正常访问。
经过一番摸索后，我发现了不用配置监听器的方法，
在applicationContext.xml文件中引入springmvc-config.xml文件

<import resource="classpath:springmvc-config.xml"/>

这种方法也能正常使用，具体原理还不清楚。