JSP彩色验证码
生成有4个随机数字和杂乱背景的图片，数字和背景颜色会改变，服务器端刷新（用history.go(-1)也会变）
原型参考alibaba http://china.alibaba.com/member/showimage
产生验证码图片的文件-----image.jsp
<%@ page contenttype="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %>
<%!
color getrandcolor(int fc,int bc){//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);
// 在内存中创建图象
int width=60, height=20;
bufferedimage image = new bufferedimage(width, height, bufferedimage.type_int_rgb);
// 获取图形上下文
graphics g = image.getgraphics();
//生成随机类
random random = new random();
// 设定背景色
g.setcolor(getrandcolor(200,250));
g.fillrect(0, 0, width, height);
//设定字体
g.setfont(new font("times new roman",font.plain,18));
//画边框
//g.setcolor(new color());
//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<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);
}
// 取随机产生的认证码(4位数字)
string srand="";
for (int i=0;i<4;i++){
string rand=string.valueof(random.nextint(10));
srand+=rand;
// 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);
}
// 将认证码存入session
session.setattribute("rand",srand);
// 图象生效
g.dispose();
// 输出图象到页面
imageio.write(image, "jpeg", response.getoutputstream());
%>
---------------使用验证码图片的文件---------a.jsp------------------------------------
<%@ page contenttype="text/html;charset=gb2312" %>
<!doctype html public "-//w3c//dtd html 4.01 transitional//en">
<html>
<head>
<title>认证码输入页面</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>系统产生的认证码：</td>
<td><img border=0 src="image.jsp"></td>
</tr>
<tr>
<td align=left>输入上面的认证码：</td>
<td><input type=text name=rand maxlength=4 value=""></td>
</tr>
<tr>
<td colspan=2 align=center><input type=submit value="提交检测"></td>
</tr>
</form>
</body>
</html>
-----------------验证的页面----------check.jsp
<%@ page contenttype="text/html; charset=gb2312" language="java" import="java.sql.*" errorpage="" %>
<html>
<head>
<title>认证码验证页面</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");
%>
系统产生的认证码为： <%= rand %><br>
您输入的认证码为： <%= input %><br>
<br>
<%
if (rand.equals(input)) {
%>
<font color=green>输入相同，认证成功！</font>
<%
} else {
%>
<font color=red>输入不同，认证失败！</font>
<%
}
%>
</body>
</html>