Java生成带计算的验证码

import java.awt.Color;  

import java.awt.Font;  

import java.awt.Graphics;  

import java.awt.image.BufferedImage;  

import java.io.IOException;  

import java.io.OutputStream;  

import java.util.Random;  

import javax.imageio.ImageIO;  

import javax.servlet.ServletException;  

import javax.servlet.http.HttpServlet;  

import javax.servlet.http.HttpServletRequest;  

import javax.servlet.http.HttpServletResponse;  

import javax.servlet.http.HttpSession;  

/** 

 * 生成带简单运算(加、减)的验证码 

 */  

public class CaptchaServlet extends HttpServlet {     

    private static final long serialVersionUID = 5581444867349884055L;  

    private static final Random random = new Random();   

    public void doGet(HttpServletRequest request, HttpServletResponse response)     

            throws ServletException, IOException {     

        this.doPost(request, response);     

    }  

    public void doPost(HttpServletRequest request, HttpServletResponse response)     

            throws ServletException, IOException {  

        String type = request.getParameter("type");  

        if (null == type || "".equals(type)) {  

            return;  

        }  

        if ("genarate".equals(type)) {  

            int width = 100, height = 30;  

            //创建BufferedImage对象，设置图片的长度宽度和色彩。     

            BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);     

            OutputStream os = response.getOutputStream();     

            //取得Graphics对象，用来绘制图片     

            Graphics g = image.getGraphics();     

            //绘制图片背景和文字,释放Graphics对象所占用的资源。     

            g.setColor(getRandColor(50, 100));     

            //设置内容生成的位置     

            g.fillRect(0, 0, width, height);     

            //设置内容的字体和大小     

            g.setFont(new Font("Times New Roman", Font.BOLD, 20));     

            //图片背景上随机生成100干扰线，避免通过图片识别破解验证码     

            for (int i = 0; i < 100; i++) {     

                //设置内容的颜色：主要为生成图片背景的线条     

                g.setColor(getRandColor(100, 200));  

                int x = random.nextInt(width);     

                int y = random.nextInt(height);     

                int xl = random.nextInt(width);     

                int yl = random.nextInt(height);     

                g.drawLine(x, y, x+1, y+1);     

            }     

            g.setColor(getRandColor(100, 250));  

            // 将运算式绘到图片中  

            g.drawString(createEquation(request), 2, 22);  

            //释放此图形的上下文以及它使用的所有系统资源，类似于关闭流     

            g.dispose();     

             //通过ImageIO对象的write静态方法将图片输出。     

            ImageIO.write(image, "JPEG", os);     

            os.close();    

            return;  

        } else if ("validate".equals(type)){  

            String captchaNo = request.getParameter("captchaNo");  

            if (null == captchaNo || "".equals(captchaNo)) {  

                response.getWriter().print("false");  

            }  

            if (captchaNo.equals(request.getSession().getAttribute("captchaNo").toString())) {  

                response.getWriter().print("true");  

            } else {  

                response.getWriter().print("false");  

            }  

            //校验过的验证码立即失效,换成一个随机数  

//          request.getSession().removeAttribute("captchaNo");  

//          request.getSession().setAttribute("captchaNo", Math.round(Math.random()*10000));  

            return;  

        }  

    }     

    /**   

     * 生成随机颜色  

     * @param fc   

     * @param bc   

     * @return   

     */    

    private Color getRandColor(int fc, int bc) {     

        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);     

    }     

    /** 

     * 生成运算式  

     * @param request 

     * @return 

     */  

    private String createEquation(HttpServletRequest request) {  

         // 定义数组存放加减二个运算符     

         char[] arr = {'+', '-'};     

         // 生成10以内的随机整数num1     

         int num1 = random.nextInt(30);     

         // 生成一个0-2之间的随机整数operate     

         int operate = random.nextInt(2);     

         // 生成10以内的随机整数num1     

         int num2 = random.nextInt(30);     

         // 避免出现除数为0的情况    

         if (num1 < num2) {  

                int temp = num1;  

                num1 = num2;  

                num2 = temp;  

             }  

         // 运算结果     

         int captchaNo = 0;     

         // 假定position值0/1分别代表”+”,”-”，计算前面操作数的运算结果     

         switch (operate) {     

         case 0:     

             captchaNo = num1 + num2;     

             break;     

         case 1:     

             captchaNo = num1 - num2;   

             break;       

         }     

         // 将生成的验证码值(即运算结果的值)放到session中，以便于后台做验证。     

         HttpSession session = request.getSession();       

         session.setAttribute("captchaNo", captchaNo);   

         return num1+" "+ arr[operate]+" "+num2+" = ?";  

    }  

}