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();%>