使用重写url机制实现验证码换一张功能

2019-11-19 15:56:09

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来源：转载

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重写URL机制：为了保证一个url的地址唯一，可每次向服务器传递的参数不一样即可。

由数据请求的抱头信息可分析到：抱头信息包括http协议，IP地址，端口号，工程名，请求参数列表，要想访问的资源不发生变化，只能变化参数连表。

此处在实现验证码的换一张的功能时，就是利用了改变参数列表的值进行刷新。

详细代码实现：

<%@page import="javax.imageio.ImageIO"%> <%@page import="java.awt.Font"%> <%@page import="java.awt.Color"%> <%@page import="java.awt.Graphics"%> <%@page import="java.awt.image.BufferedImage"%> <%@ page contentType="image/jpeg" language="java" import="java.util.*" pageEncoding="UTF-8"%> <% int w=100; int h=30; BufferedImage bi=new BufferedImage(w,h,BufferedImage.TYPE_INT_RGB); Graphics g=bi.getGraphics(); Color c=g.getColor(); Font f=g.getFont();  Random r=new Random(); Color bg=new Color(150+r.nextInt(100),150+r.nextInt(100),150+r.nextInt(100)); g.setColor(bg); g.fillRect(0, 0, w, h); String code=""; for(int i=1;i<=4;i++){ int num=r.nextInt(10); code=code+num; Color num_c=new Color(r.nextInt(150),r.nextInt(150),r.nextInt(150)); g.setColor(num_c); g.drawString(String.valueOf(num), 20*i, h/2); } request.getSession().setAttribute("code", code); //清空缓存 response.setHeader("pragma", "bo-cache"); response.setHeader("cache-control", "bo-cache"); response.addDateHeader("expires", 0); ImageIO.write(bi, "jpeg", response.getOutputStream()); out.close();  %>

添加登录页面：

<%@ page contentType="text/html; charset=utf-8" language="java" import="java.util.*" pageEncoding="UTF-8"%> <%String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html>  <head>   <base href="<%=basePath%>" rel="external nofollow" >   <title>My JSP 'login.jsp' starting page</title>   <meta http-equiv="pragma" content="no-cache">   <meta http-equiv="cache-control" content="no-cache">   <meta http-equiv="expires" content="0">     <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">   <meta http-equiv="description" content="This is my page">   <!--   <link rel="stylesheet" type="text/css" href="styles.css" rel="external nofollow" >   -->   <script type="text/javascript"> function changeimage(){ var d=new Date();//生成时间戳， document.getElementById("img").src="image.jsp?t="+d;//由变化的时间使参数连表发生变化，url重写 } </script>  </head>  <body>  <font color="red">${requestScope.msg }</font>   <form action="loginServlet" method="post">   name:<input type="text" name="uname"><br>   pwd:<input type="pwd" name="upwd"><br>   code:<input type="text" name="code" size="5"><img id="img" alt="" src="image.jsp "><a onclick="changeimage()">换一张</a><br>   <input type="submit" >   </form>  </body> </html>

利用时间的变化，每次生成时间戳，传参给请求的url，达到重写url的目的，从而实现了换一张的刷新功能。