读取容器配置参数---context-param和init-param

web.xml里面可以定义两种参数：
(1)application范围内的参数，存放在servletcontext中，在web.xml中配置如下：
<context-param>
<param-name>context/param</param-name>
<param-value>avalible during application</param-value>
</context-param>
<context-param>

<param-name>context/param</param-name>

<param-value>avalible during application</param-value>

</context-param>

(2)servlet范围内的参数，只能在servlet的init()方法中取得，在web.xml中配置如下：

<servlet>
<servlet-name>MainServlet</servlet-name>
<servlet-class>com.wes.controller.MainServlet</servlet-class>
<init-param>
<param-name>param1</param-name>
<param-value>avalible in servlet init()</param-value>
</init-param>
<load-on-startup>0</load-on-startup>
</servlet>
<servlet>

<servlet-name>MainServlet</servlet-name>

<servlet-class>com.wes.controller.MainServlet</servlet-class>

<init-param>

<param-name>param1</param-name>

<param-value>avalible in servlet init()</param-value>

</init-param>

<load-on-startup>0</load-on-startup>

</servlet>

在servlet中可以通过代码分别取用：

package com.wes.controller;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;

public class MainServlet extends HttpServlet{

public MainServlet(){
super();
}
public void init() throws ServletException ...{
System.out.println("下面的两个参数param1是在servlet中存放的");
System.out.println(this.getInitParameter("param1"));
System.out.println("下面的参数是存放在servletcontext中的");
System.out.println(getServletContext().getInitParameter("context/param"));
}