產生驗證碼圖片的文件image.jsp
<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %>
<%!Color getRandColor(int fc,int bc){//給定範圍獲得隨機顏色 
Random random = new Random(); if(fc>255) fc=255; if(bc>255) bc=255; int r=fc+random.nextInt(bc-fc); int g=fc+random.nextInt(bc-fc); int b=fc+random.nextInt(bc-fc); 
return new Color(r,g,b); }%><%//設置頁面不緩存response.setHeader("Pragma","No-cache");response.setHeader("Cache-Control","no-cache");response.setDateHeader("Expires", 0);// 在內存中創建圖象int width=60, height=20;BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);// 獲取圖形上下文Graphics g = image.getGraphics();//生成隨機類Random random = new Random();// 設定背景色g.setColor(getRandColor(200,250));g.fillRect(0, 0, width, height);//設定字體g.setFont(new Font("Times New Roman",Font.PLAIN,18));//畫邊框//g.setColor(new Color());//g.drawRect(0,0,width-1,height-1);// 隨機產生155條幹擾線，使圖象中的認證碼不易被其它程序探測到g.setColor(getRandColor(160,200));for (int i=0;i<155;i++){ int x = random.nextInt(width); int y = random.nextInt(height); int xl = random.nextInt(12); int yl = random.nextInt(12); g.drawLine(x,y,x+xl,y+yl);}// 取隨機產生的認證碼(4位數字)String sRand="";for (int i=0;i<4;i++){ String rand=String.valueOf(random.nextInt(10)); sRand+=rand; // 將認證碼顯示到圖象中 g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));//調用函數出來的顏色相同，可能是因爲種子太接近，所以只能直接生成 g.drawString(rand,13*i+6,16);}// 將認證碼存入SESSIONsession.setAttribute("rand",sRand);// 圖象生效g.dispose();// 輸出圖象到頁面ImageIO.write(image, "JPEG", response.getOutputStream());%>
使用驗證碼圖片的文件a.jsp
<%@ page contentType="text/html;charset=gb2312" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><title>認證碼輸入頁面</title><meta http-equiv="Content-Type" content="text/html; charset=gb2312"><META HTTP-EQUIV="Pragma" CONTENT="no-cache"> <META HTTP-EQUIV="Cache-Control" CONTENT="no-cache"> <META HTTP-EQUIV="Expires" CONTENT="0"> </head><body><form method=post action="check.jsp"><table> <tr> <td align=left>系統產生的認證碼：</td> <td> <img border=0 p"></td></tr> <tr> <td align=left>輸入上面的認證碼：</td> <td> <input type=text maxlength=4 value=""></td></tr> <tr> <td colspan=2 align=center> <input type=submit value="提交檢測"></td></tr></form></body></html>
驗證的頁面check.jsp
<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %><html><head><title>認證碼驗證頁面</title><meta http-equiv="Content-Type" content="text/html; charset=gb2312"><META HTTP-EQUIV="Pragma" CONTENT="no-cache"> <META HTTP-EQUIV="Cache-Control" CONTENT="no-cache"> <META HTTP-EQUIV="Expires" CONTENT="0"> </head><body><% String rand = (String)session.getAttribute("rand"); String input = request.getParameter("rand");%> 系統產生的認證碼爲： <%= rand %<br> 您輸入的認證碼爲： <%= input %><br><br><% if (rand.equals(input)) {%><font color=green>輸入相同，認證成功！</font><% } else {%><font color=red>輸入不同，認證失敗！</font><% }%></body></html>
