JavaWeb 使用Session实现一次性验证码

表单

<form action="loginServlet" method="post">
  请输入验证码：<input type="text" name="code" />
  <img src="getCodeServlet" /><br />
  <button type="submit">提交</button>
</form>

载入页面时，会自动请求getCodeServlet，获取图片（验证码）。

getCodeServlet，产生验证码

@WebServlet("/getCodeServlet")
public class GetCodeServlet extends HttpServlet {
    //验证码的宽、高
    private static int WIDTH=80;
    private static int HEIGHT=25;

    //绘制背景
    private void drawBg(Graphics g){
        //rgb
        g.setColor(new Color(128, 128, 128));
        //绘制矩形。x,y,wigth,height
        g.fillRect(0,0,WIDTH,HEIGHT);
        //随机绘制100个干扰点
        Random random=new Random();
        for (int i=0;i<100;i++){
            //产生(0,1）上的小数，*WIDTH|HEIGHT，再取整也行
            int x=random.nextInt(WIDTH);
            int y=random.nextInt(HEIGHT);
            g.drawOval(x,y,1,1);

            //干扰点的颜色也可以随机，随机产生red，green，blue即可
            //g.setColor(new Color(red,green,blue));
        }
    }


    //绘制验证码
    private void drawCode(Graphics g,char[] code){
        g.setColor(Color.BLACK);
        //字体、样式（多个时竖线分隔）、字号
        g.setFont(new Font("serif",Font.ITALIC|Font.BOLD,18));
        //在不同位置绘制验证码字符，参数：要绘制的String、横、纵坐标。+""是为了char转String。
        g.drawString(code[0]+"",1,17);
        g.drawString(code[1]+"",16,15);
        g.drawString(code[2]+"",31,18);
        g.drawString(code[3]+"",46,16);
    }

    //随机产生4位验证码
    private char[] getCode(){
        String chars="0123456789QWERTYUIOPASDFGHJKLZXCVBNMqwertyuiopasdfghjklzxcvbnm";
        char[] code=new char[4];
        Random random=new Random();
        for (int i=0;i<4;i++){
            //[0,62)
            int index= random.nextInt(62);
            code[i]=chars.charAt(index);
        }
        return code;
    }


    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
        HttpSession session = request.getSession();
        ServletOutputStream sos = response.getOutputStream();
        response.setContentType("image/jpeg");

        //设置浏览器不缓存此图片
        response.setHeader("Pragma","No-cache");
        response.setHeader("Cache-Control","no-cache");
        response.setDateHeader("Expires",0);

        //创建内存图片
        BufferedImage bufferedImage = new BufferedImage(WIDTH, HEIGHT, TYPE_INT_RGB);
        Graphics g= bufferedImage.getGraphics();
        char[] code=getCode();
        //将验证码放到session域中。session对象要在提交响应之前获得
        session.setAttribute("code",new String(code));
        drawBg(g);
        drawCode(g,code);
        g.dispose();

        //将图片输出到浏览器
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ImageIO.write(bufferedImage,"JPEG",baos);
        baos.writeTo(sos);
        baos.close();
        sos.close();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        doPost(request,response);
    }
}

loginServlet，处理表单

@WebServlet("/loginServlet")
public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        HttpSession session = request.getSession();
        String trueCode= (String) session.getAttribute("code");
        String code=request.getParameter("code");

        if (code.equals(trueCode)){
            response.getWriter().write("验证码正确");
        }
        else {
            response.getWriter().write("验证码错误");
        }
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request,response);
    }
}

上面的处理方式要区分验证码的大小写。

不区分大小写：

//先转换为全大写|全小写，再判断
        trueCode=trueCode.toLowerCase();
        code=code.toLowerCase();

        //trueCode=trueCode.toUpperCase();
        //code=trueCode.toUpperCase();