servlet 写前台验证码

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servlet中内容

import java.awt.Color;import java.awt.Font;import java.awt.Graphics;import java.awt.Graphics2D;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;public class ResponseDemo4 extends HttpServlet {private static final long serialVersionUID = 1L;public static final int WIDTH = 120;public static final int HEIGHT = 35;public ResponseDemo4() {super();}protected void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {// 指定图片的宽和高和其类型BufferedImage image = new BufferedImage(WIDTH, HEIGHT,BufferedImage.TYPE_INT_RGB);Graphics g = image.getGraphics(); // 得到一张图片// 1、设置背景色setBackGround(g);// 2、设置边框setBorder(g);// 3、画干扰线drawRandomLine(g);// 4、写随机数drawRandomNum((Graphics2D)g);// 5、图形写给浏览器response.setContentType("image/jpeg");//发头控制浏览器不要缓存response.setDateHeader("expries", -1);response.setHeader("Catch-Control", "no-cache");response.setHeader("Param", "no-cache");ImageIO.write(image, "jpg", response.getOutputStream());}//设置背景颜色private void setBackGround(Graphics g) {g.setColor(Color.WHITE);g.fillRect(0, 0, WIDTH, HEIGHT);}             //设置边框        private void setBorder(Graphics g) {              g.setColor(Color.BLUE);               g.drawRect(1, 1, WIDTH-2, HEIGHT-2);  //前两个是左上角坐标，后两个分别是宽和高}//画干扰线    private void drawRandomLine(Graphics g) {g.setColor(Color.GREEN);for(int i = 0;i<5;i++){int x1 = new Random().nextInt(WIDTH);int y1 = new Random().nextInt(HEIGHT);int x2 = new Random().nextInt(WIDTH);int y2 = new Random().nextInt(WIDTH);g.drawLine(x1, y1, x2, y2); //定位，两点确定一条直线}}    //产生随机数字private void drawRandomNum(Graphics2D g) {        g.setColor(Color.RED);g.setFont(new Font("宋体",Font.BOLD,20));String base = "\u7684\u4e00\u4e86\u662f\u6212\u4e0d\u5728\u4eba\u4eec\u6709\u6765";        int x = 10;for(int i=0;i<=4;i++){int degree = new Random().nextInt()%30; //生成0-30的随机数String ch =base.charAt(new Random().nextInt(base.length()))+"";g.rotate(degree*Math.PI/180, x, 20);//设置旋转角度g.drawString(ch, x, 20);  //字符位于此图形上下文坐标系统的（x,20）位置处g.rotate(-degree*Math.PI/180,x,20);x=x+30;}}protected void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {this.doGet(request, response);}}

前台接收

<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title><script type="text/javascript">  function changeImage(img){

  img.src = img.src+"?" + new Date().getTime();  //相当于在地址栏后面加了一个随机数，解决了缓存的问题  }</script></head><body>  <form>    用户名：<input type="text" name = "username"><br/>    密码：<input type="password" name="password"><br/>    认证码：<input type="text" name="checkcode" >  <img src="/Day06/responseDemo4" onclick="changeImage(this)" alt="换一张" style="cursor:hand"><br/>  <!--路径写的是servlet里面对应的路径  -->  <input type="submit" value="注册">  </form></body></html>