Servlet实现验证码

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Servlet实现验证码
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.awt.*;
import java.awt.image.*;
import javax.imageio.ImageIO;

public class CheckCodeServlet extends HttpServlet
{
     private static final String CONTENT_TYPE = "text/html; charset=utf-8";
     //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()
     {
     }
}

下一个主页提交的Servlet：

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class LogonFormServlet extends HttpServlet
{
    public void service(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException
    {
        response.setContentType("text/html;charset=GB2312");
        PrintWriter out = response.getWriter();

        HttpSession session = request.getSession(false);
        if(session == null)
        {
            out.println("验证码处理问题!");
            return;
        }

        String savedCode = (String)session.getAttribute("check_code");
        if(savedCode == null)
        {
            out.println("验证码处理问题!");
            return;
        }

        String checkCode = request.getParameter("check_code");
        if(!savedCode.equals(checkCode))
        {
            /*验证码未通过，不从Session中清除原来的验证码，
            以便用户可以后退回登录页面继续使用原来的验证码进行登录*/
            out.println("验证码无效!");
            return;
        }
        /*验证码检查通过后，从Session中清除原来的验证码，
        以防用户后退回登录页面继续使用原来的验证码进行登录*/
        session.removeAttribute("check_code");
        out.println("验证码通过，服务器正在校验用户名和密码!");
    }
}

web.xml
<servlet>
        <servlet-name>CheckCodeServlet</servlet-name>
        <servlet-class>CheckCodeServlet</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>LogonFormServlet</servlet-name>
        <servlet-class>LogonFormServlet</servlet-class>
    </servlet>
    ……
    <servlet-mapping>
        <servlet-name>CheckCodeServlet</servlet-name>
        <url-pattern>/authImage</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>LogonFormServlet</servlet-name>
        <url-pattern>/servlet/LogonFormServlet</url-pattern>
    </servlet-mapping>

JSP页面加上：
<img src="authImage">