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ServletContext is a configuration Object which is created when web application is started. It contains different initialization parameter that can be configured in web.xml.
You are developing a web application where you want to access the email of administrator in whole application. You want to set this email id @ one location and every Servlet and Jsp can access that email. In that case you will take the help of ServletContext. You can add this email in servletcontext via init parameter in web.xml. Now this value (Email id of administrator) will be available to every Jsp and Servlet in the web application.
Step 1: Servlet container reads the DD (Deployment Descriptor – web.xml) and creates the name/value string pair for each <context-param> when web application is getting started.
Step 2: Container creates the new Instance of ServletContext.
Note*: ServletContext is an Interface.
Step 3: Servlet container gives the ServletContext a reference to each name/value pair of the context init parameter.
Step 4: Every servlet and JSP in the same web application will now has access to this ServletContext.
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<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:applicationContext.xml</param-value>
</context-param>
</web-app>
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Now you know that you can set init parameter in ServletContext & this Servletcontext will be initialized when application starts. After initialization this servletcontext will be available to all servlet and jsp. But what if you want to perform some kind of action when context initialization/destruction process happens. This is the situation when you will take the help of servletcontextlistener.
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原文地址：http://www.cnblogs.com/hephec/p/4556594.html
