JavaEE中，实现登录时进行校验验证码的功能

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;



public class RandomServlet extends HttpServlet {

	
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		// 在内存中创建图象,width,height：控制图片的宽和高
		int width = 111, height = 45;
		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, 20));
		// 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 < 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);
		}
		// 取随机产生的认证码(6位数字)
		String sRand = "";
		for (int i = 0; i < 6; i++) {
			String rand = String.valueOf(random.nextInt(10));
			sRand += rand;
			// 将认证码显示到图象中
			g.setColor(new Color(20 + random.nextInt(110), 20 + random
					.nextInt(110), 20 + 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, 30);//控制六个验证码数字在图中的位置
		}
		// 图象生效
		g.dispose();
		
		try {
			ImageIO.write(image, "JPEG", response.getOutputStream());
		} catch (Exception e) {
			System.out.println("验证码图片产生出现错误：" + e.toString());
		}
		//保存验证码到Session
		request.getSession().setAttribute("randStr", sRand);
		
	}


	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		this.doGet(request, response);
	}
	/*
	 * 给定范围获得随机颜色
	 */
	private 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);
	}
}

function changeYZM(){

	//获取图片，修改图片的地址
	$("#YZM").attr("src","random.jpg?time="+new Date().toLocaleString());
	}

 <li class="yzm">
	    <span><input name="YZM" type="text" value="请输入验证码" /></span>
	    <cite><img alt="" id="YZM" onclick="changeYZM()" src="random.jpg"></cite> 
</li>

		//获取输入的验证码
		String YZM=request.getParameter("YZM");//自己输入的验证码
		String randStr=(String) request.getSession().getAttribute("randStr");//随机生成的验证码
		if (YZM==null || !YZM.equals(randStr)) {//进行比对
			request.setAttribute("error", "验证码错误");
			request.getRequestDispatcher("/login.jsp").forward(request, response);
			return;//跳出该程序，不执行下面的代码
		}