web.xml配置，请高人分析

1、
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/applicationContext*.xml</param-value>
</context-param>
    2、
<context-param>
<description>
Key of the system property that should specify the root
directory of this web app. Applied by WebAppRootListener or
Log4jConfigListener.
</description>
<param-name>webAppRootKey</param-name>
<param-value>webapp.root</param-value>
</context-param>
    3、
<context-param>
<description>
Location of the Log4J config file, for initialization and
refresh checks. Applied by Log4jConfigListener.
</description>
<param-name>log4jConfigLocation</param-name>
<param-value>/WEB-INF/classes/log4j.xml</param-value>
</context-param>
    4、
<listener>
<listener-class>
org.springframework.web.context.ContextLoaderListener
</listener-class>
</listener>
    5、
<listener>
<description>
Leave the listener commented-out if using JBoss
</description>
<listener-class>
org.springframework.web.util.Log4jConfigListener
</listener-class>
</listener>
谁能帮我分析一下4、5这两个监听有什么用处，什么时间被触发。