小工具-jsp实现验证码功能

<%@ 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) {//给定范围获得随机颜色
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);
}%>
<%
//设置页面不缓存
response.setHeader("Pragma", "No-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0);

//生成随机验证码
Random random = new Random();
String sRand = "";
for (int i = 0; i < 4; i++) {
String rand = String.valueOf(random.nextInt(10));
sRand += rand;
}
// 将认证码存入SESSION
session.setAttribute("CHECK_NUMBER_KEY", sRand);

// 在内存中创建图象
int width = 55;
int height = 20;
BufferedImage image = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);

// 获取图形上下文
Graphics g = image.getGraphics();

// 设定背景色
g.setColor(getRandColor(200, 250));
g.fillRect(0, 0, width, height);

//设定字体
g.setFont(new Font("serif", Font.CENTER_BASELINE, 16));

//画边框
//g.setColor(new Color(1));
//g.drawRect(0,0,width-1,height-1);

// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
g.setColor(getRandColor(160, 200));
for (int i = 0; i < 100; 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);
}

for (int i = 0; i < 4; i++) {
String rand = sRand.substring(i, i + 1);
// 将认证码显示到图象中
g.setColor(new Color(20 + random.nextInt(110), 20 + random
.nextInt(110), 20 + random.nextInt(110)));
//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
g.drawString(rand, 13 * i + 6, 16);
}

// 图象生效
g.dispose();

// 输出图象到页面
try {
ImageIO.write(image, "JPEG", response.getOutputStream());
} catch (Exception e) {
}
out.clear();
out = pageContext.pushBody();
%>

<!-- 验证码 -->
<tr>
<td width="100"><img border="0" src="${pageContext.request.contextPath}/images/check.jpg" width="84" height="20"></td>
<td>
<input type="text" name="checkNumber" id="checkNumber" style="width: 20 px;" value=""  maxlength="4">
img src="${pageContext.request.contextPath}/image.jsp" id="checkNumberImage" name="checkNumberImage" height="20" style="cursor:hand;" title="点击切换下一张图片" onclick="changeImage();"/>
</td>

</tr>