验证码实现详解

实现类：

<%@ page pageEncoding="GBK"%>
<%@ page contentType="image/jpeg"
import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*,java.io.File"%>

<%!
//给定范围获得随机颜色
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);
}%>

<%
//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 = 70, height = 25;
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));

// 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 < 200; 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(5位数字)
//完整的一个验证码(用来存放拼接结果)
String sRand = "";
String letter="abcdefghijklmnopqrstuvwsyzABCDEFGHIJKLNMOPQRSTUVWSYZ";
for (int i = 0; i < 5; i++) {

//随机英文
char randChar=letter.charAt(random.nextInt(letter.length()));
String randLetter=String.valueOf(randChar);
//0到10的随机数字
  String randNum=String.valueOf(random.nextInt(10));

  String rand = (random.nextInt(10)%2==1)?randNum:randLetter;
  sRand += rand;
  // 将认证码显示到图象中
  g.setColor(new Color(20 + random.nextInt(110), 40 + random
  .nextInt(110), 60 + 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());
out.clear();
out = pageContext.pushBody();

ImageIO.write(image,"JPEG",new File("../webapps/myshop/images/out.jpg"));

%>

ServletResponse res

调用：<img border=0 src="verifyCode">

验证输入正确性：

String input = request.getParameter("verify");//输入的验证码
String rand = (String) session.getAttribute("rand");//系统的验证码

if (rand.equals(input)) {

do something....

｝