登陆验证码的实现

package Serverlet;

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.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

    /**
     * Servlet implementation class LoginServlet
     */
    @WebServlet(name="VerifyCode.do", urlPatterns="/VerifyCode.do") 
    public class VerifyCodeServlet extends HttpServlet {
        private static final long serialVersionUID = 1L;
           
        /**
         * @see HttpServlet#HttpServlet()
         */
        public VerifyCodeServlet() {
            super();
            // TODO Auto-generated constructor stub
        }
        
        /**
         * Initialization of the servlet. <br>
         * @throws ServletException if an error occurs
         */
        public void init() throws ServletException {
            // Put your code here
        }

        /**
         * Destruction of the servlet. <br>
         */
        public void destroy() {
            super.destroy(); // Just puts "destroy" string in log
            // Put your code here
        }

        /**
         * The doGet method of the servlet. <br>
         *
         * This method is called when a form has its tag value method equals to get.
         * 
         * @param request the request send by the client to the server
         * @param response the response send by the server to the client
         * @throws ServletException if an error occurred
         * @throws IOException if an error occurred
         */
        public void doGet(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {

            this.doPost(request, response);
        }

        /**
         * The doPost method of the servlet. <br>
         *
         * This method is called when a form has its tag value method equals to post.
         * 
         * @param request the request send by the client to the server
         * @param response the response send by the server to the client
         * @throws ServletException if an error occurred
         * @throws IOException if an error occurred
         */
        public void doPost(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {

            response.setContentType("image/jpeg");
            request.setCharacterEncoding("utf-8");
            response.setCharacterEncoding("utf-8");
            
            String uuid = request.getParameter("uuid");
            
            System.out.println(uuid);
            
            //声明验证码
            int width = 80;
            int height = 30;
            String data = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789abcdefghijklmnpqrstuvwxyz";    //随机字符字典，其中0，o，1，I 等难辨别的字符最好不要
            Random random = new Random();//随机类
            //1 创建图片数据缓存区域（核心类）
            BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);//创建一个彩色的图片
            //2 获得画板(图片，ps图层)，绘画对象。
            Graphics g = image.getGraphics();
            //3 选择颜色，画矩形3，4步是画一个有内外边框的效果
            g.setColor(Color.BLACK);
            g.fillRect(0, 0, width, height);
            //4白色矩形
            g.setColor(Color.WHITE);
            g.fillRect(1, 1, width-2, height-2);
            
            /**1 提供缓存区域，为了存放4个随机字符，以便存入session */
            StringBuilder builder = new StringBuilder();
            
            //5 随机生成4个字符
            
            //设置字体颜色
            g.setFont(new Font("宋体", Font.BOLD&Font.ITALIC, 25));
            
            for(int i = 0 ; i < 4 ;i ++){
                //随机颜色
                g.setColor(new Color(random.nextInt(255),random.nextInt(255), random.nextInt(255)));
                
                //随机字符
                int index = random.nextInt(data.length());
                String str = data.substring(index, index + 1);
                
                //String str = code.substring(i,i+1);
                
                /**2 缓存*/
                builder.append(str);
                
                //写入
                g.drawString(str, (width / 6) * (i + 1) , 20);                     
            }
            
            //给图中绘制噪音点，让图片不那么好辨别
            for(int j=0,n=random.nextInt(100);j<n;j++){
                g.setColor(Color.RED);
                g.fillRect(random.nextInt(width),random.nextInt(height),1,1);//随机噪音点
            }
            
            /**3 获得随机数据，并保存session*/
            String tempStr = builder.toString();
            request.getSession().setAttribute("sessionCacheData",tempStr);
            
            //.. 生成图片发送到浏览器 --相当于下载
            ImageIO.write(image, "jpg", response.getOutputStream());

        }
    }