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();