java--验证码实现

验证码：

主要用于防止猜测密码，很多软件通过自动猜测密码的方式来破解密码，如果设置了验证码，那么黑客编写的软件就不能正确识别验证码，从而实现不能通过软件尝试破解密码的作用，我们在登录系统时，需要输入验证码，它延长了操作者的时间对用户体验很不利，为什么这么多网站还要用呢？欢迎访问博客：验证码有什么用？为什么要用验证码？

怎么用？

1、配置web.xml文件：

<servlet>
	<servlet-name>AuthImageServlet</servlet-name>
	<servlet-class>com.orcl.drp.util.servlet.AuthImageServlet</servlet-class>
</servlet>
<servlet-mapping>
    	<servlet-name>AuthImageServlet</servlet-name>
    	<url-pattern>/servlet/AuthImageServlet</url-pattern>
 </servlet-mapping>

2、AuthImageServlet类代码：

public class AuthImageServlet extends HttpServlet   
{   
  
    private static final String CONTENT_TYPE = "text/html; charset=gb2312";   
    //设置字母的大小,大小   
    private Font mFont = new Font("Times New Roman", Font.PLAIN, 17);   
    public void init() throws ServletException   
    {   
        super.init();   
    }   
    Color getRandColor(int fc,int bc)   
    {   
        Random random = new Random();   
        if(fc>255) fc=255;   
        if(bc>255) bc=255;   
        int r=fc+random.nextInt(bc-fc);   
        int g=fc+random.nextInt(bc-fc);   
        int b=fc+random.nextInt(bc-fc);   
        return new Color(r,g,b);   
    }   
  
    public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException   
    {   
        response.setHeader("Pragma","No-cache");   
        response.setHeader("Cache-Control","no-cache");   
        response.setDateHeader("Expires", 0);   
        //表明生成的响应是图片   
        response.setContentType("image/jpeg");   
           
        int width=100, height=18;   
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);   
           
        Graphics g = image.getGraphics();   
        Random random = new Random();   
        g.setColor(getRandColor(200,250));   
        g.fillRect(1, 1, width-1, height-1);   
        g.setColor(new Color(102,102,102));   
        g.drawRect(0, 0, width-1, height-1);   
        g.setFont(mFont);   
  
        g.setColor(getRandColor(160,200));   
  
        //画随机线   
        for (int i=0;i<155;i++)   
        {   
            int x = random.nextInt(width - 1);   
            int y = random.nextInt(height - 1);   
            int xl = random.nextInt(6) + 1;   
            int yl = random.nextInt(12) + 1;   
            g.drawLine(x,y,x + xl,y + yl);   
        }   
  
        //从另一方向画随机线   
        for (int i = 0;i < 70;i++)   
        {   
            int x = random.nextInt(width - 1);   
            int y = random.nextInt(height - 1);   
            int xl = random.nextInt(12) + 1;   
            int yl = random.nextInt(6) + 1;   
            g.drawLine(x,y,x - xl,y - yl);   
        }   
  
        //生成随机数,并将随机数字转换为字母   
        String sRand="";   
        for (int i=0;i<6;i++)   
        {   
            int itmp = random.nextInt(26) + 65;   
            char ctmp = (char)itmp;   
            sRand += String.valueOf(ctmp);   
            g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));   
            g.drawString(String.valueOf(ctmp),15*i+10,16);   
        }   
  
        HttpSession session = request.getSession(true);   
        session.setAttribute("rand",sRand);   
        g.dispose();   
        ImageIO.write(image, "JPEG", response.getOutputStream());   
    }   
    public void destroy()   
    {   
    }   
}  

3、jsp页面关键代码：

String authCode = request.getParameter("authCode");
//输入的与session中作比较，忽略大小写
if (!authCode.trim().equalsIgnoreCase((String)session.getAttribute("rand"))) {
	out.println("验证码不正确！");
}

<TD align=left><FONT face="verdana, arial, helvetica, sans-serif"
        size=-1>验证码：</FONT>
</TD>
<TD align=left>
        <INPUT name="authCode" type="text" size="6" maxlength="6">

        <img src="${pageContext.request.contextPath }/servlet/AuthImageServlet">
</TD>

实现效果：