jsp 生成网页验证码的Servlet

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;

/**
 * 生成图形验证码的Servlet
 */
public class ImageCodeMakerServlet extends HttpServlet {

	public void doGet(HttpServletRequest req,HttpServletResponse resp)
			throws ServletException,IOException {
		doPost(req,resp);
	}

	/**
	 * @see javax.servlet.http.HttpServlet#void
	 *      (javax.servlet.http.HttpServletRequest,*      javax.servlet.http.HttpServletResponse)
	 */
	public void doPost(HttpServletRequest req,IOException {

		// 首先设置页面不缓存
		resp.setHeader("Pragma","No-cache");
		resp.setHeader("Cache-Control","no-cache");
		resp.setDateHeader("Expires",0);

		// 定义图片的宽度和高度
		int width = 90,height = 40;
		// 创建一个图像对象
		BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
		// 得到图像的环境对象
		Graphics g = image.createGraphics();

		Random random = new Random();
		// 用随机颜色填充图像背景
		g.setColor(getRandColor(180,250));
		g.fillRect(0,width,height);
		for (int i = 0; i < 5; i++) {
			g.setColor(getRandColor(50,100));
			int x = random.nextInt(width);
			int y = random.nextInt(height);
			g.drawOval(x,y,4,4);
		}
		// 设置字体，下面准备画随机数
		g.setFont(new Font("",Font.PLAIN,40));
		// 随机数字符串
		String sRand = "";
		for (int i = 0; i < 4; i++) {
			// 生成四个数字字符
			String rand = String.valueOf(random.nextInt(10));
			sRand += rand;
			// 生成随机颜色
			g.setColor(new Color(20 + random.nextInt(80),20 + random
					.nextInt(100),20 + random.nextInt(90)));
			// 将随机数字画在图像上
			g.drawString(rand,(17 + random.nextInt(3)) * i + 8,34);

			// 生成干扰线
			for (int k = 0; k < 12; k++) {
				int x = random.nextInt(width);
				int y = random.nextInt(height);
				int xl = random.nextInt(9);
				int yl = random.nextInt(9);
				g.drawLine(x,x + xl,y + yl);
			}
		}

		// 将生成的随机数字字符串写入Session
		req.getSession().setAttribute("randcode",sRand);
		// 使图像生效
		g.dispose();
		// 输出图像到页面
		ImageIO.write(image,"JPEG",resp.getOutputStream());
	}

	/**
	 * 产生一个随机的颜色
	 * 
	 * @param fc
	 *            颜色分量最小值
	 * @param bc
	 *            颜色分量最大值
	 * @return
	 */
	public 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);
	}
}