web.xml配备学习

web.xml配置学习

          <!--
		- Configures Log4J for this web app.
		- As this context specifies a context-param "log4jConfigLocation", its file path
		- is used to load the Log4J configuration, including periodic refresh checks.
		-
		- Would fall back to default Log4J initialization (non-refreshing) if no special
		- context-params are given.
		-
		- Exports a "web app root key", i.e. a system property that specifies the root
		- directory of this web app, for usage in log file paths.
		- This web app specifies "petclinic.root" (see log4j.properties file).
	-->
	<!-- Leave the listener commented-out if using JBoss -->
	<!--
	<listener>
		<listener-class>org.springframework.web.util.Log4jConfigListener</listener-class>
	</listener>
	-->

	<!--
		- Loads the root application context of this web app at startup,
		- by default from "/WEB-INF/applicationContext.xml".
		- Note that you need to fall back to Spring's ContextLoaderServlet for
		- J2EE servers that do not follow the Servlet 2.4 initialization order.
		-
		- Use WebApplicationContextUtils.getWebApplicationContext(servletContext)
		- to access it anywhere in the web application, outside of the framework.
		-
		- The root context is the parent of all servlet-specific contexts.
		- This means that its beans are automatically available in these child contexts,
		- both for getBean(name) calls and (external) bean references.
	-->
	<listener>
		<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
	</listener>

首先需要配置ContextLoaderListener，如果要配置Log4jConfigListener，那么一定要配置在ContextLoaderListener的前面。
ContextLoaderListener是加载应用的上下方环境（context），如果把这个context记为A，那么A下面还可以有子Context，这些Context配置在以*-servlet.xml的文件中。可以配置多个*-servlet.xml，它们共享context A。
Log4j的配置文件可以定制：

        <context-param>
		<param-name>log4jConfigLocation</param-name>
		<param-value>/WEB-INF/classes/log4j.properties</param-value>
	</context-param>