java Web圖片驗證碼

1.在body中加入如下代碼：
<script language="javascript">
    function changeCode() {
        document.getElementById('checkImg').src = 'GetCaptcha?temp='+ (new Date().getTime().toString(36));
        return false;
    }
</script>

<center>
        <form>
            驗證碼: <input type="text" maxlength="113" οnmοuseοver="this.style.background='pink'" οnmοuseοut="this.style.background='white'">
             <img src="GetCaptcha" alt="驗證碼" name="checkImg" id="checkImg" onClick="changeCode()" />
        </form>
    </center>

2.在web.xml中配置如下代碼：
    <servlet>
        <servlet-name>GetCaptcha</servlet-name>
        <servlet-class>com.eims.util.GetCaptcha</servlet-class>
    </servlet>


    <servlet-mapping>
        <servlet-name>GetCaptcha</servlet-name>
        <url-pattern>/GetCaptcha</url-pattern>
    </servlet-mapping>

3.在com.eims.util.GetCaptcha包中加入如下工具類
    package com.eims.util;


import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.util.*;
import java.awt.*;
import java.awt.image.*;

import javax.imageio.*;
/**
 *
 * @author mzba
 *
 */
public class GetCaptcha extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public GetCaptcha() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("image/jpeg");
        response.setHeader("Pragma", "No-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setDateHeader("Expires", 0);
        HttpSession session = request.getSession();
        int width = 75, height = 25;
        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, 24));
        g.setColor(getRandColor(160, 200));
        g.drawRect(0, 0, width - 1, height - 1);
        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 + 14, 20);
        }

        session.setAttribute("vcode", sRand);

        g.dispose();
        ImageIO.write(image, "JPEG", response.getOutputStream());
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

    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);
    }

}

4.在servlet中使用如下代碼進行驗證：
        /**
     * 驗證用戶輸入的驗證碼輸入的是否正確
     * @param request
     * @param response
     * @throws ServletException
     * @throws IOException
     */
    public boolean checkValidationCode(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        boolean flag=true;
        HttpSession session=request.getSession();
        String validationRightCode=(String)session.getAttribute("vcode");
        String validationUserCode=request.getParameter("validationCode");
        if(!validationRightCode.equals(validationUserCode)){
            request.setAttribute("information","驗證碼輸入不正確！");
            flag=false;
            RequestDispatcher rd=request.getRequestDispatcher("login/dealwith.jsp");
            rd.forward(request, response);
        }
        return flag;
    }