javaweb实现验证码功能

在javaweb的用户注册与登陆功能时，有时为了防止漏洞或者大量注册，可以使用验证码功能，下面是验证码的一个简单实现

验证码类

public class ValiImg extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setDateHeader("Expires", -1);
        response.setHeader("Cache-Control", "no-Cache");
        response.setHeader("pragma", "no-Cache");

        int height = 30;
        int width = 30*4;
        BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
        Graphics2D g =  (Graphics2D) image.getGraphics();

        //1.填充矩形
        g.setColor(Color.GREEN);
        g.fillRect(0, 0, width, height);

        //2.画边框
        g.setColor(Color.BLACK);
        g.drawRect(0, 0, width-1, height-1);

        //3.话干扰线
        g.setColor(Color.RED);
        for(int i = 0;i<5;i++){
            g.drawLine(getRandInt(0,width), getRandInt(0,height), getRandInt(0,width), getRandInt(0,height));
        }
        //4.随机生成字符写到图片上 
         String base = "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";
        g.setFont(new Font("宋体",Font.BOLD,20));
        g.setColor(Color.BLACK);
        StringBuffer buffer = new StringBuffer();
        for(int i=0;i<4;i++){
            double c = getRandInt(-45, 45)/180F*Math.PI;
            g.rotate(c, 5+width/4*i, 22);
            String s = base.charAt(getRandInt(0,base.length()-1))+"";
            buffer.append(s);
            g.drawString(s, 5+width/4*i, 22);
            g.rotate(-c, 5+width/4*i, 22);
        }
        System.out.println(buffer.toString());
        request.getSession().setAttribute("valistr", buffer.toString());
        //5.释放资源
        g.dispose();
        //6.利用ImageIO进行输出
        ImageIO.write(image, "jpg", response.getOutputStream());

    }

    Random random = new Random();
    public int getRandInt(int begin,int end){
        return random.nextInt(end-begin)+begin;
    }

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

HTML可以动态刷新验证码

<tr>
                <td>验证码:</td>
                <td><input type="text" name="valistr"/></td>
                <td id="valistr_msg">${msg }</td>
            </tr>
            <tr>
                <td><input type="submit" value="注册用户"/></td>
                <td><img src="ValiImg" onclick="changeImg(this)" style="cursor: pointer;"/></td>

function changeImg(img)
    {
        img.src=img.src+"?time="+new Date().getTime();
    }

在servlet中校验验证码是否正确


//较验验证码
String valistr1=request.getParameter("valistr");
String valistr2=(String) request.getSession().getAttribute("valistr");
if(valistr1==null||valistr2==null||!valistr1.equals(valistr2))
{
request.setAttribute("msg", "<font color='red'>验证码不正确!</font> ");
request.getRequestDispatcher("register.jsp").forward(request, response);
return;
}


效果如下