Jsp生成页面验证码的方法

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image.jsp 

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<%@ page contentType="image/JPEG"
import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*,java.awt.Color"
pageEncoding="GBK"%>
<%!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
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("rand", sRand);
g.dispose();
ImageIO.write(image, "JPEG", response.getOutputStream());
%>
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引用验证码:

<script language="javascript"> 
function loadimage(){
  document.getElementById("randImage").src = "image.jsp?"+Math.random();
}
</script>

 

<img name="randImage" id="randImage" src="image.jsp" width="60" height="20" border="1" align="absmiddle" onclick="javascript:loadimage()" style= "cursor:hand" >

判断验证码是否正确:

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<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %> 
<%
String rand = (String)session.getAttribute("rand");
String input = request.getParameter("rand");
if(rand.equals(input)){
out.print("<script>alert('验证通过!');</script>");
} else{
out.print("<script>alert('请输入正确的验证码!');location.href='login.jsp';</script>");
}
%>
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