jsp实现简单验证码的方法

<%@ 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);
}
%>
<%
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);
}
session.setAttribute("rand",sRand);
g.dispose();
ImageIO.write(image, "JPEG", response.getOutputStream());
response.getOutputStream().flush();
response.getOutputStream().close();
out.clear();
out=pageContext.pushBody();
%>