Java 随机验证码

step 1 : 生成随机验证码的页面 /common/randomNumber.jsp

<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,com.sun.image.codec.jpeg.*,java.util.*" %>
<%!
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);
}
%>
<%
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","no-cache");
response.setDateHeader("Expires", 0);

out.clear();
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);
}
session.setAttribute("rand",sRand);
g.dispose();
ServletOutputStream outStream = response.getOutputStream();
JPEGImageEncoder encoder =JPEGCodec.createJPEGEncoder(outStream);
encoder.encode(image);
outStream.close();
out.clear();
out = pageContext.pushBody();
%>

step 2 :  使用验证码的页面

<input type="text" name="ckcode" size="4" /> 
 <img name="CheckNumber" border=0 src="/common/randomNumber.jsp" 
  onclick="this.src='/common/randomNumber.jsp?'+Math.random()" width="60" height="20" alt=""　／>

 

 

step 3 : servlet 验证

String ccode=(String)request.getSession().getAttribute("rand");
String code=request.getParameter("ckcode");
if(!code.equals(ccode)){
     //验证码不正确
}