这里有新鲜出炉的精品教程,程序狗速度看过来!
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。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。具体详细代码大家参考下本文
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。
总结
来源: http://www.phperz.com/article/17/0905/343904.html