web.xml的初始化参数:context-param,init-param

1、初始化参数

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>

(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>

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("下面的参数是存放在servletcontext中的");
         System.out.println(getServletContext().getInitParameter("context/param"));

            System.out.println("下面的两个参数param1是在servlet中存放的");

         System.out.println(this.getInitParameter("param1"));
       }
}

第一种参数在servlet里面可以通过getServletContext().getInitParameter("context/param")得到
第二种参数只能在servlet的init()方法中通过this.getInitParameter("param1")取

2、初始化参数获取

 

<context-param>
  <param-name>count</param-name>
  <param-value>1200</param-value>
  </context-param>

 

 

<servlet>
    <description>loginServlet</description>
    <display-name>loginServlet</display-name>
    <servlet-name>loginServlet</servlet-name>
    <servlet-class>loginServlet</servlet-class>
    <init-param>
      <description>系统初始化数</description>
      <param-name>num</param-name>
      <param-value>100</param-value>
    </init-param>
  </servlet>
  <servlet-mapping>
    <servlet-name>loginServlet</servlet-name>
    <url-pattern>/loginServlet</url-pattern>
  </servlet-mapping>

 

 

获取参数的方法以及异同

 

String username=request.getParameter("username");
  response.setCharacterEncoding("gb2312");
  System.out.println("getServletContext()："+getServletContext());
  ServletContext context=getServletConfig().getServletContext();
  String num=context.getInitParameter("num");// <init-param> 获取不到值
  String count=context.getInitParameter("count");//<context-param> 获取到值
  System.out.println("num："+num);//null
  System.out.println("count："+count);//1200
  System.out.println("num："+getServletConfig().getInitParameter("num"));//100获取到值
  System.out.println("count："+getServletConfig().getInitParameter("count"));//null获取不到值

  
  System.out.println("request.getSession().getServletContext()："+request.getSession().getServletContext());
  request.setAttribute("username", username);
  PrintWriter out=response.getWriter();
  out.println("获取的用户名是："+username);

 

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1、URL中含有两个问号'?? '的处理

http://a.tbcdn.cn/??s/kissy/1.2.0/kissy-min.js,p/global/1.0/global-min.js,p/fp/2012/core.js,p/fp/2012/fp/module.js,p/fp/2012/fp/util.js,p/fp/2012/fp/directpromo.js?t=2012080620120925.js

解决：先以/*做全匹配，再分配给其余servlet进行处理， url的匹配顺序，参考：http://tianya23.blog.51cto.com/1081650/1001568

@Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
          throws IOException, ServletException {
      HttpServletRequest httpRequest = null;
      if (request instanceof HttpServletRequest) {
          httpRequest = (HttpServletRequest) request;
      } else {
          throw new RuntimeException("not http request");
      }
      String queryString = httpRequest.getQueryString();
      if (queryString != null && queryString.startsWith("?")) {
          request.getRequestDispatcher("/taobao").forward(httpRequest, response);
      } else {
          chain.doFilter(httpRequest, response);
      }
  }