java实现验证码

java验证码的实现(一)
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1.ImageServlet类的实现：
package com.mobile.control;
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 ImageServlet extends HttpServlet {
       public void doGet(HttpServletRequest request,
HttpServletResponse response)
                     throws ServletException, IOException {
              this.doPost(request, response);
       }
       // 生成数字和字母的验证码
       public void doPost(HttpServletRequest request,
HttpServletResponse response)
                     throws ServletException, IOException {
              BufferedImage img = new BufferedImage(68, 22,
                            BufferedImage.TYPE_INT_RGB);
              // 得到该图片的绘图对象
              Graphics g = img.getGraphics();
              Random r = new Random();
&