含字母、数字的Servlet图形验证码

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class AuthImg extends HttpServlet {

// 设置图形验证码中字符串的字体和大小
private Font font = new Font("Arial Black", Font.PLAIN, 16);

public void init() throws ServletException {
   super.init();
}

// 生成随机颜色
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);
}

@Override
protected void service(HttpServletRequest request,
    HttpServletResponse response) throws ServletException, IOException {
   //
   response.setHeader("Pragma", "No-cache");
   response.setHeader("Cache-Control", "No-cache");
   response.setDateHeader("Expires", 0);
   response.setContentType("image/jpeg");

   // 指定图形验证码图片的大小
   int width = 100, height = 18;
   // 生成一张新图片
   BufferedImage image = new BufferedImage(width, height,
     BufferedImage.TYPE_INT_RGB);
   // 在图片中绘制内容
   Graphics g = image.getGraphics();
   Random random = new Random();
   g.setColor(getRandColor(200, 250));
   g.fillRect(1, 1, width - 1, height - 1);
   g.setColor(new Color(102, 102, 102));
   g.drawRect(0, 0, width - 1, height - 1);

   g.setFont(font);

   // 随机生成线条
   g.setColor(getRandColor(160, 200));
   for (int i = 0; i < 155; i++) {
    int x1 = random.nextInt(6) + 1;
    int y1 = random.nextInt(12) + 1;
    int x2 = random.nextInt(width - 1);
    int y2 = random.nextInt(width - 1);
    g.drawLine(x1, y1, x1 + x2, y1 + y2);
   }
   // 随机生成线条
   for (int i = 0; i < 70; i++) {
    int x1 = random.nextInt(6) + 1;
    int y1 = random.nextInt(12) + 1;
    int x2 = random.nextInt(width - 1);
    int y2 = random.nextInt(width - 1);
    g.drawLine(x1, y1, x1 - x2, y1 - y2);
   }
   // 该变量用于保存系统生成的随机字符串
   String randStr = "";
   for (int i = 0; i < 6; i++) {
    // 获得一个随机字符
    String tmp = getRandChar();
    randStr += tmp;
    // 将系统生成的随机字符添加到图形验证码上
    g.setColor(new Color(20 + random.nextInt(110), 20 + random
      .nextInt(110), 20 + random.nextInt(110)));
    g.drawString(tmp, 15 * i + 10, 15);
   }
   HttpSession session = request.getSession(true);
   // 将系统生成的图形验证码放到Session中
   session.setAttribute("rand", randStr);
   g.dispose();
   // 输出图形验证码
   ImageIO.write(image, "JPEG", response.getOutputStream());

}

// 生成随机字符
private String getRandChar() {
   int rand = (int) Math.round(Math.random() * 2);
   long itmp = 0;
   char ctmp = '\u0000';
   // 根据rand的值来决定来生成一个大写字母、小写字母和数字
   switch (rand) {
   // 生成大写字母
   case 1:
    itmp = Math.round(Math.random() * 25 + 65);
    ctmp = (char) itmp;
    return String.valueOf(ctmp);
    // 生成小写字母
   case 2:
    itmp = Math.round(Math.random() * 25 + 90);
    ctmp = (char) itmp;
    return String.valueOf(ctmp);
    // 生成数字
   default:
    itmp = Math.round(Math.random() * 9);
    return String.valueOf(itmp);
   }
}
}

页面上调用：

请输入验证码：
   <input type="text">
   <img src="AuthImg" id="authImg" onclick="this.src='AuthImg?now='+new Date()" alt="点击刷新" >