实现服务器向客户端发送图片（验证码应用）.txt

  服务器端向客户端发送
        String createTypeFlag = request.getParameter("createTypeFlag");//接收客户端传递的createTypeFlag标识
        //1.在内存中创建一张图片
        BufferedImage bi = new BufferedImage(WIDTH, HEIGHT,BufferedImage.TYPE_INT_RGB);
        //2.得到图片
        Graphics g = bi.getGraphics();
        //3.设置图片的背影色
        setBackGround(g);
        //4.设置图片的边框
        setBorder(g);
        //5.在图片上画干扰线
        drawRandomLine(g);
        //6.写在图片上随机数
        //String random = drawRandomNum((Graphics2D) g,"ch");//生成中文验证码图片
        //String random = drawRandomNum((Graphics2D) g,"nl");//生成数字和字母组合的验证码图片
        //String random = drawRandomNum((Graphics2D) g,"n");//生成纯数字的验证码图片
        //String random = drawRandomNum((Graphics2D) g,"l");//生成纯字母的验证码图片
        String random = drawRandomNum((Graphics2D) g,createTypeFlag);//根据客户端传递的createTypeFlag标识生成验证码图片
        //7.将随机数存在session中
        request.getSession().setAttribute("checkcode", random);
        //8.设置响应头通知浏览器以图片的形式打开
        response.setContentType("image/jpeg");//等同于response.setHeader("Content-Type", "image/jpeg");
        //9.设置响应头控制浏览器不要缓存
        response.setDateHeader("expries", -1);
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Pragma", "no-cache");
        //10.将图片写给浏览器
        ImageIO.write(bi, "jpg", response.getOutputStream());


客户端接收
<img alt="验证码看不清，换一张" src="${pageContext.request.contextPath}/servlet/DrawImage" id="validateCodeImg" onclick="changeImg()">