java实现验证码完整版

    <servlet>  
        <servlet-name>ImageServlet</servlet-name>  
        <servlet-class>org.servlet.ImageServlet</servlet-class>  
    </servlet>  
    <servlet-mapping>  
        <servlet-name>ImageServlet</servlet-name>  
        <url-pattern>/ImageServlet</url-pattern>  
    </servlet-mapping>  

    import javax.servlet.ServletException;  
    import javax.servlet.http.HttpServlet;  
    import javax.servlet.http.HttpServletRequest;  
    import javax.servlet.http.HttpServletResponse;  
      
    import com.farm.web.tool.RandomValidateCode;  
      
    public class ImageServlet extends HttpServlet {  
      
        private static final long serialVersionUID = 1L;  
      
        public void doGet(HttpServletRequest request,HttpServletResponse response)  
                throws ServletException,IOException {  
      
            response.setContentType("image/jpeg");// 设置相应类型,告诉浏览器输出的内容为图片  
            response.setHeader("Pragma","No-cache");// 设置响应头信息，告诉浏览器不要缓存此内容  
            response.setHeader("Cache-Control","no-cache");  
            response.setDateHeader("Expire",0);  
            RandomValidateCode randomValidateCode = new RandomValidateCode();  
            try {  
                randomValidateCode.getRandcode(request,response);// 输出图片方法  
            } catch (Exception e) {  
                e.printStackTrace();  
            }  
        }  
      
        public void doPost(HttpServletRequest request,IOException {  
            doGet(request,response);  
        }  
      
    }  

    import java.awt.Color;  
    import java.awt.Font;  
    import java.awt.Graphics;  
    import java.awt.image.BufferedImage;  
    import java.util.Random;  
      
    import javax.imageio.ImageIO;  
    import javax.servlet.http.HttpServletRequest;  
    import javax.servlet.http.HttpServletResponse;  
    import javax.servlet.http.HttpSession;  
      
    public class RandomValidateCode {  
      
        public static String validateCode = null;  
        public static final String RANDOMCODEKEY = "RANDOMVALIDATECODEKEY";// 放到session中的key  
        private Random random = new Random();  
        private String randString = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";// 随机产生的字符串  
      
        private int width = 80;// 图片宽  
        private int height = 26;// 图片高  
        private int lineSize = 40;// 干扰线数量  
        private int stringNum = 4;// 随机产生字符数量  
      
        /* 
         * 获得字体 
         */  
        private Font getFont() {  
            return new Font("Fixedsys",Font.CENTER_BASELINE,18);  
        }  
      
        /* 
         * 获得颜色 
         */  
        private Color getRandColor(int fc,int bc) {  
            if (fc > 255)  
                fc = 255;  
            if (bc > 255)  
                bc = 255;  
            int r = fc + random.nextInt(bc - fc - 16);  
            int g = fc + random.nextInt(bc - fc - 14);  
            int b = fc + random.nextInt(bc - fc - 18);  
            return new Color(r,g,b);  
        }  
      
        /** 
         * 生成随机图片 
         */  
        public void getRandcode(HttpServletRequest request,HttpServletResponse response) {  
            HttpSession session = request.getSession();  
            // BufferedImage类是具有缓冲区的Image类,Image类是用于描述图像信息的类  
            BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_BGR);  
            Graphics g = image.getGraphics();// 产生Image对象的Graphics对象,改对象可以在图像上进行各种绘制操作  
            g.fillRect(0,width,height);  
            g.setFont(new Font("Times New Roman",Font.ROMAN_BASELINE,18));  
            g.setColor(getRandColor(110,133));  
            // 绘制干扰线  
            for (int i = 0; i <= lineSize; i++) {  
                drowLine(g);  
            }  
            // 绘制随机字符  
            String randomString = "";  
            for (int i = 1; i <= stringNum; i++) {  
                randomString = drowString(g,randomString,i);  
            }  
            session.removeAttribute(RANDOMCODEKEY);  
            session.setAttribute(RANDOMCODEKEY,randomString);  
            validateCode = randomString.toUpperCase();  
            g.dispose();  
            try {  
                ImageIO.write(image,"JPEG",response.getOutputStream());// 将内存中的图片通过流动形式输出到客户端  
            } catch (Exception e) {  
                e.printStackTrace();  
            }  
        }  
      
        /* 
         * 绘制字符串 
         */  
        private String drowString(Graphics g,String randomString,int i) {  
            g.setFont(getFont());  
            g.setColor(new Color(random.nextInt(101),random.nextInt(111),random  
                    .nextInt(121)));  
            String rand = String.valueOf(getRandomString(random.nextInt(randString  
                    .length())));  
            randomString += rand;  
            g.translate(random.nextInt(3),random.nextInt(3));  
            g.drawString(rand,13 * i,16);  
            return randomString;  
        }  
      
        /* 
         * 绘制干扰线 
         */  
        private void drowLine(Graphics g) {  
            int x = random.nextInt(width);  
            int y = random.nextInt(height);  
            int xl = random.nextInt(13);  
            int yl = random.nextInt(15);  
            g.drawLine(x,y,x + xl,y + yl);  
        }  
      
        /* 
         * 获取随机的字符 
         */  
        public String getRandomString(int num) {  
            return String.valueOf(randString.charAt(num));  
        }  
    }  

    <tr>  
        <td>  
            <div align="right">  
                验证码：  
            </div>  
        </td>  
        <td>  
            <input style="width: 65px" id="validatecode" name="validatecode" type="text" />  
        </td>  
        <td>  
            <img title="看不清楚,换一张？" style="cursor: pointer;"  
                onclick="javascript:refresh(this);"  
                src="<PF:basePath/>/ImageServlet">  
        </td>  
    </tr>  

    function refresh(obj) {  
        obj.src = "<PF:basePath/>/ImageServlet?"+Math.random();    
    }  

if(RandomValidateCode.validateCode!=null&&validatecode.trim().toUpperCase().equals(RandomValidateCode.validateCode)){  
    System.out.println("验证码正确");  
}