JSP 中实现验证码

提供一个比较好用的验证码，是纯数字型的！在webRoot下面创建一个image.jsp.代码为：

<%@ page language="java" pageEncoding="UTF-8"%>
<%@ page contentType="image/jpeg"
import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"%>
<%!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);
}%>
<%
out.clear();//这句针对resin服务器，如果是tomacat可以不要这句
out=pageContext.pushBody();
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);
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);
}
// 将认证码存入SESSION
session.setAttribute("code", sRand);
g.dispose();
ImageIO.write(image, "JPEG", response.getOutputStream());
%>

它把生成的验证码用保持到session中，命名为code,所有在servlet中把你输入的验证码和系统生产验证码对比！

在页面中引用的话需要

<!-- 验证码 -->

<tr>

<td width="13%" height="35" class="top_hui_text"><span class="login_txt"> 验证码:    </span></td>

<td ><input class=wenbenkuang name="txtCode" id="txtCode" type="text" maxLength=4 size=10></td>

<td><img src="image.jsp" onclick="this.src='image.jsp?id='+Math.random();" alt="点击刷新验证码！"/> </td>这句话是关键字，连接到创建的image.jsp的路径上

</tr>