java使用servlet实现验证码

package com.zyc.demo;  import java.awt.Color; import java.awt.Font; import java.awt.Graphics; import java.awt.image.BufferedImage; import java.io.IOException; 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;  public class DrewImage extends HttpServlet{   /**    *    */   private static final long serialVersionUID = 1505032428319459075L;   private final Font mFont =       new Font("Arial Black", Font.PLAIN, 16);     private final int IMG_WIDTH = 100;     private final int IMG_HEIGTH = 18;     private 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);       response.setContentType("image/jpeg");       BufferedImage image = new BufferedImage         (IMG_WIDTH , IMG_HEIGTH , BufferedImage.TYPE_INT_RGB);       Graphics g = image.getGraphics();       Random random = new Random();       g.setColor(getRandColor(200 , 250));       g.fillRect(1, 1, IMG_WIDTH - 1, IMG_HEIGTH - 1);       g.setColor(new Color(102 , 102 , 102));       g.drawRect(0, 0, IMG_WIDTH - 1, IMG_HEIGTH - 1);       g.setColor(getRandColor(160,200));       for (int i = 0 ; i < 30 ; i++)       {         int x = random.nextInt(IMG_WIDTH - 1);         int y = random.nextInt(IMG_HEIGTH - 1);         int xl = random.nextInt(6) + 1;         int yl = random.nextInt(12) + 1;         g.drawLine(x , y , x + xl , y + yl);       }       g.setColor(getRandColor(160,200));       for (int i = 0 ; i < 30 ; i++)       {         int x = random.nextInt(IMG_WIDTH - 1);         int y = random.nextInt(IMG_HEIGTH - 1);         int xl = random.nextInt(12) + 1;         int yl = random.nextInt(6) + 1;         g.drawLine(x , y , x - xl , y - yl);       }       g.setFont(mFont);       String sRand = "";       for (int i = 0 ; i < 4 ; i++)       {         String tmp = getRandomChar();         sRand += tmp;         g.setColor(new Color(20 + random.nextInt(110)           ,20 + random.nextInt(110)           ,20 + random.nextInt(110)));         g.drawString(tmp , 15 * i + 10,15);       }       HttpSession session = request.getSession(true);       session.setAttribute("rand" , sRand); //     System.out.println("写入session"+sRand);       g.dispose();       ImageIO.write(image, "JPEG", response.getOutputStream());     }     private String getRandomChar()     {       int rand = (int)Math.round(Math.random() * 2);       long itmp = 0;       char ctmp = '/u0000';       switch (rand)       {         case 1:           itmp = Math.round(Math.random() * 25 + 65);           ctmp = (char)itmp;           return String.valueOf(ctmp);         case 2:           itmp = Math.round(Math.random() * 25 + 97);           ctmp = (char)itmp;           return String.valueOf(ctmp);         default :           itmp = Math.round(Math.random() * 9);           return itmp + "";       }     } } 

<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">  <display-name>IndustryDemo</display-name>  <welcome-file-list>   <welcome-file>index.html</welcome-file>   <welcome-file>index.htm</welcome-file>   <welcome-file>index.jsp</welcome-file>   <welcome-file>default.html</welcome-file>   <welcome-file>default.htm</welcome-file>   <welcome-file>default.jsp</welcome-file>  </welcome-file-list>    <servlet>    <servlet-name>img</servlet-name>    <servlet-class>com.zyc.demo.DrewImage</servlet-class>  </servlet>    <servlet-mapping>    <servlet-name>img</servlet-name>    <url-pattern>/img.do</url-pattern>  </servlet-mapping>   </web-app> 

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> <% String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %>  <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html>  <head>   <base href="<%=basePath%>">      <title>My JSP 'yanzhengma.jsp' starting page</title>      <meta http-equiv="pragma" content="no-cache">   <meta http-equiv="cache-control" content="no-cache">   <meta http-equiv="expires" content="0">     <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">   <meta http-equiv="description" content="This is my page">   <!--   <link rel="stylesheet" type="text/css" href="styles.css">   -->   </head>    <body>   <img </body> </html>