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：