web.xml里面定义在servletcontex、Servlet和Filter的参数：

web.xml里面可以参数：

(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>

(2)servlet范围内的参数，只能在相应的servlet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>

在servlet中可以通过代码分别取用：

 publicclassMainServlet extendsHttpServlet {

     

      public MainServlet() {

        super();

        }

      publicvoid 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"));

     }

}

(3)filter过滤器范围内的参数，只能在相应的过滤器中取得，在web.xml中配置如下：

  <filter>

      <filter-name>ecoding</filter-name>

      <filter-class>cn.com.filtes.EcodingFilter</filter-class>

      <init-param>

         <param-name>req</param-name>

         <param-value>UTF-8</param-value>

      </init-param>

      <init-param>

         <param-name>res</param-name>

         <param-value>text/html;charset=UTF-8</param-value>

      </init-param>

   </filter>

在自定义的过滤器中

publicvoid doFilter(ServletRequest request, ServletResponseresponse,

          FilterChain chain) throws IOException,ServletException {

       request.setCharacterEncoding(filterConfig.getInitParameter("req"));

       response.setContentType(filterConfig.getInitParameter("res"));

       chain.doFilter(request, response);

    }

第一种参数在servlet里面可以通过getServletContext().getInitParameter("context/param")得到
第二种参数中通过this.getInitParameter("param1")取得

这里的this是指的是：getServletConfig()获取的ServletConfig对象