Filter对Request的改变：HttpServletRequestWrapper的工作原理

Filter对Request的改变：HttpServletRequestWrapper的工作原理
马克- to-win：马克 java社区：防盗版实名手机尾号： 73203。
马克-to-win：有了HttpServletResponseWrapper的基础，就好理解HttpServletRequestWrapper了。无疑它就是想在Request到达服务器之前，先把它处理一下。比如过滤掉一些政治敏感字。意义嘛，也好理解。比如n个html页面都需要过滤，如果都在 n个servlet当中过滤的话，会造成未来代码维护困难。马克-to-win：HttpServletRequestWrapper的使用方法就是靠着：1）MarkToWinRequestWrapper  hsr =new MarkToWinRequestWrapper((HttpServletRequest)request); 和 2）chain.doFilter(hsr, response);
这两句话以后MarkToWinRequestWrapper的实例hsr取代了request，之后在servlet调用的request.getParameter(String name)方法当然就是MarkToWinRequestWrapper类的getParameter方法。如果servlet想调用request的其他方法，MarkToWinRequestWrapper这个类也可以覆盖掉它。

例 1.2.8

package com;
import javax.servlet.http.*;
public class MarkToWinRequestWrapper extends HttpServletRequestWrapper {
    public MarkToWinRequestWrapper(HttpServletRequest request) {
        super(request);
    }
    public String getParameter(String param) {
        System.out.println("参数是 is" + param);
        String paramValue = super.getParameter(param);
        System.out.println("修改前 in wrapper" + paramValue);
        if (param.equals("name")) {
            paramValue = paramValue.replaceAll("mark-to-win", "马克-to-win");
            System.out.println("修改后  in wrapper" + paramValue);
        } else if (param.equals("age")) {
            paramValue = paramValue.replaceAll("30", "40");
            System.out.println("修改后  in wrapper" + paramValue);
        }
        return paramValue;
    }
}





package com;
import java.io.IOException;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.PrintWriter;
public class MarkToWinFilter implements Filter {
    public void destroy() {
    }
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        MarkToWinRequestWrapper  hsr =new MarkToWinRequestWrapper((HttpServletRequest)request);
/*下句话以后hsr取代了request，之后在servlet调用的request.getParameter(String name)方法当然就是MarkToWinRequestWrapper类的getParameter方法*/
        chain.doFilter(hsr, response);
    }
    public void init(FilterConfig fConfig) throws ServletException {
    }
}


package com;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.*;
public class ServletHello1 extends HttpServlet {
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        request.setCharacterEncoding("GBK");
        String name = request.getParameter("name");
        System.out.println("name in Servlet 修改后 is "+ name);
        String age = request.getParameter("age");
        System.out.println("age in Servlet 修改后 is "+ age);
    }
}


add.jsp:

<%@ page contentType="text/html; charset=GBK" %>
<html>
<body>
<center><h3>书籍描述 mark-to-win</h3></center>
<form action="MarkToWinServlet" method="post">
作者名称<INPUT TYPE="TEXT" NAME="name">
年龄<INPUT TYPE="TEXT" NAME="age">
<input type="submit" name="Submit" value="提交">
</form>
</body>
</html>










Console里面的书出如下：

参数是 isname
修改前 in wrappermark-to-win
修改后  in wrapper马克-to-win
name in Servlet 修改后 is 马克-to-win
参数是 isage
修改前 in wrapper30
修改后  in wrapper40
age in Servlet 修改后 is 40