重寫URL機制:為了保證一個url的位址唯一,可每次傳遞給伺服器的參數不一樣即可。此處在實作驗證碼的換一張的功能時,就是利用了改變參數清單的值進行刷新。具體詳細程式碼大家參考下本文
重寫URL機制:為了確保一個url的位址唯一,可每次傳遞給伺服器的參數不一樣即可。
由資料請求的抱頭資訊可分析到:抱頭資訊包括http協議,IP位址,連接埠號,工程名,請求參數列表,要想存取的資源不發生變化,只能變化參數連表。
此處在實作驗證碼的換一張的功能時,就是利用了改變參數清單的值來重新整理。
詳細程式碼實作:
<%@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(); %>
新增登入頁面:
<%@ 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>
利用時間的變化,每次產生時間戳,傳參給請求的url,達到重寫url的目的,從而實現了換一張的刷新功能。
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