validateCode.jsp：
<%@ page 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%>">
<title>兩組驗證碼</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">
</head>
<body>
Two Validate Code: <br>
<img src="vc_1.jsp" />
<img src="vc_2.jsp" />
</body>
</html>
vc_1.jsp：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ page import="com.ysx.system.actions.*"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>驗證碼測試</title>
</head>
<body>
<form name="f1" method="post" action="login.jsp">
<div>
<%
Yzm a = new Yzm();
a.service(request, response);
out.clear();
out = pageContext.pushBody();
%>
</div>
</form>
</body>
</html>
vc_2.jsp：
<%@ page
import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"%>
<%@ page import="java.io.OutputStream"%>
<%!Color getRandColor(int fc, int bc) {
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);
}%>
<%
try {
response.setHeader("Pragma", "No-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0);
int width = 60, height = 20;
BufferedImage image = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
OutputStream os = response.getOutputStream();
Graphics g = image.getGraphics();
Random random = new Random();
g.setColor(getRandColor(200, 250));
g.fillRect(0, 0, width, height);
g.setFont(new Font("Times New Roman", Font.PLAIN, 18));
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);
}
String sRand = "";
for (int i = 0; i < 4; i++) {
String rand = String.valueOf(random.nextInt(10));
sRand += rand;
g.setColor(new Color(20 + random.nextInt(110), 20 + random
.nextInt(110), 20 + random.nextInt(110)));
g.drawString(rand, 13 * i + 6, 16);
}
session.setAttribute("rand", sRand);
g.dispose();
ImageIO.write(image, "JPEG", os);
os.flush();
os.close();
os = null;
response.flushBuffer();
out.clear();
out = pageContext.pushBody();
} catch (IllegalStateException e) {
System.out.println(e.getMessage());
e.printStackTrace();
}
%>
Yzm.java：
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.*;
import javax.servlet.http.*;
public class Yzm extends HttpServlet 
{
public static final long serialVersionUID = 1L;
// 驗證碼圖片的寬度。
private int width = 60;
// 驗證碼圖片的高度。
private int height = 20;
protected void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, java.io.IOException {
BufferedImage buffImg = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
Graphics2D g = buffImg.createGraphics();
// 創建一個隨機數生成器類。
Random random = new Random();
g.setColor(Color.WHITE);
g.fillRect(0, 0, width, height);
// 創建字體，字體的大小應該根據圖片的高度來定。
Font font = new Font("Times New Roman", Font.PLAIN, 18);
// 設置字體。
g.setFont(font);
// 畫邊框。
g.setColor(Color.BLACK);
g.drawRect(0, 0, width - 1, height - 1);
// 隨機產生160條干擾線，使圖象中的認證碼不易被其它程序探測到。
g.setColor(Color.GRAY);
for (int i = 0; i < 10; 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);
}
// randomCode用于保存隨機產生的驗證碼，以便用戶登錄后進行驗證。
StringBuffer randomCode = new StringBuffer();
int red = 0, green = 0, blue = 0;
// 隨機產生4位數字的驗證碼。
for (int i = 0; i < 4; i++) {
// 得到隨機產生的驗證碼數字。
String strRand = String.valueOf(random.nextInt(10));
// 產生隨機的顏色分量來構造顏色值，這樣輸出的每位數字的顏色值都將不同。
red = random.nextInt(200);
green = random.nextInt(200);
blue = random.nextInt(200);
// 產生隨機高度 13至height之間
float imght = 0;
while (imght <= 12) {
imght = Float
.parseFloat(String.valueOf(random.nextInt(height)));
}
// 用隨機產生的顏色將驗證碼繪制到圖像中。
g.setColor(new Color(red, green, blue));
g.drawString(strRand, 13 * i + 6, imght);
// 將產生的四個隨機數組合在一起。
randomCode.append(strRand);
}
// 將四位數字的驗證碼保存到Session中。
HttpSession session = req.getSession();
session.setAttribute("randomCode", randomCode.toString());
// 禁止圖像緩存。
resp.setHeader("Pragma", "no-cache");
resp.setHeader("Cache-Control", "no-cache");
resp.setDateHeader("Expires", 0);
resp.setContentType("image/jpeg");
// 將圖像輸出到Servlet輸出流中。
ServletOutputStream sos = resp.getOutputStream();
ImageIO.write(buffImg, "jpeg", sos);
sos.close();
}
}