You can use the url rewriting mechanism to change the verification code.

You can use the url rewriting mechanism to change the verification code.

URL rewriting mechanism: to ensure that the address of a url is unique, you can transmit different parameters to the server each time.

The header information of a data request can be analyzed as follows: the header information includes the http protocol, IP address, port number, project name, and request parameter list. The resources to be accessed do not change, you can only change the parameter connection table.

Here, the verification code is refreshed by changing the value of the parameter list.

Detailed code implementation:

<% @ 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 (1, 150), r. nextInt (1, 150), r. nextInt (150); g. setColor (num_c); g. drawString (String. valueOf (num), 20 * I, h/2);} request. getSession (). setAttribute ("code", code); // clear the cache response. setHeader ("pragma", "bo-cache"); response. setHeader ("cache-control", "bo-cache"); response. addDateHeader ("expires", 0); ImageIO. write (bi, "jpeg", response. getOutputStream (); out. close (); %>

Add logon page:

<% @ 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"> 
Using Time changes, a timestamp is generated each time, and parameters are passed to the requested url to rewrite the url, thus implementing the refresh function of another one.


Summary
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