package xieyuan;  
  
import java.awt.Color;  
import java.awt.Font;  
import java.awt.Graphics2D;  
import java.awt.image.BufferedImage;  
import java.io.IOException;  
import java.io.PrintWriter;  
import java.net.URLEncoder;  
import java.util.Random;  
  
import javax.servlet.ServletException;  
import javax.servlet.ServletOutputStream;  
import javax.servlet.http.HttpServlet;  
import javax.servlet.http.HttpServletRequest;  
import javax.servlet.http.HttpServletResponse;  
  
import com.sun.corba.se.impl.javax.rmi.CORBA.Util;  
import com.sun.image.codec.jpeg.JPEGCodec;  
import com.sun.image.codec.jpeg.JPEGImageEncoder;  
  
public class MyServlet extends HttpServlet {  
  
    /** 
     * Constructor of the object. 
     */  
    public MyServlet() {  
        super();  
    }  
  
    /** 
     * Destruction of the servlet. <br> 
     */  
    public void destroy() {  
        super.destroy(); // Just puts "destroy" string in log  
        // Put your code here  
    }  
  
    /** 
     * The doGet method of the servlet. <br> 
     * 
     * This method is called when a form has its tag value method equals to get. 
     *  
     * @param request the request send by the client to the server 
     * @param response the response send by the server to the client 
     * @throws ServletException if an error occurred 
     * @throws IOException if an error occurred 
     */  
    public void doGet(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
        execute(request, response);  
    }  
  
    /** 
     * The doPost method of the servlet. <br> 
     * 
     * This method is called when a form has its tag value method equals to post. 
     *  
     * @param request the request send by the client to the server 
     * @param response the response send by the server to the client 
     * @throws ServletException if an error occurred 
     * @throws IOException if an error occurred 
     */  
    public void doPost(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
        execute(request, response);  
    }  
  
      
    private static final char CHARS[]={‘2‘,‘3‘,‘4‘,‘5‘,‘6‘,‘7‘,‘8‘,‘9‘,‘A‘,‘B‘,‘C‘,‘D‘,‘E‘,  
                                       ‘F‘,‘G‘,‘H‘,‘J‘,‘K‘,‘L‘,‘M‘,‘N‘,‘P‘,‘Q‘,‘R‘,‘S‘,‘T‘,‘U‘,‘V‘,  
                                       ‘W‘,‘X‘,‘Y‘,‘Z‘  
                                      };  
    public static Random random=new Random();  
    //生成随机数字，len为需要随机数字的个数  
    public static String getRandomString(int len)  
    {  
        StringBuilder builder=new StringBuilder();  
        for(int i=0;i<len;i++)  
        {  
            builder.append(CHARS[random.nextInt(CHARS.length)]) ;  
        }  
        return builder.toString();    
    }  
    //随机生成颜色，座位背景色  
    public static Color getColor()  
    {  
        return new Color(random.nextInt(255),random.nextInt(255),random.nextInt(255));  
    }  
    //取颜色的反色  
    public static Color getReverseColor(Color color)  
    {  
        return new Color(255-color.getRed(),255-color.getGreen(),255-color.getBlue());    
    }  
      
    private void execute(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException  
    {  
        response.setCharacterEncoding("utf-8");  
        //设置返回的文件编码  
        response.setContentType("image/jpeg");  
          
        //获取随机码  
        String getRandomCode=getRandomString(5);  
        //将随机码放到Session中  
        request.getSession().setAttribute("randomcode", getRandomCode);  
        int width=100;  
        int height=30;  
        Color color=getColor();  
        Color reverseColor=getReverseColor(color);  
        //创建一个彩色图片  
        BufferedImage bi=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);  
        Graphics2D g=bi.createGraphics();  
        g.setFont(new Font(null,Font.BOLD,16));  
        g.setColor(color);  
        g.fillRect(0,0,width,height);  
        g.setColor(reverseColor);  
        g.drawString(getRandomCode, 18,20);  
        //绘制噪点,最多100个  
        for(int i=0,n=random.nextInt(100);i<n;i++)  
        {  
            g.drawRect(random.nextInt(width), random.nextInt(height), 1,1);  
        }  
        ServletOutputStream out=response.getOutputStream();  
        JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(out);  
        encoder.encode(bi);  
        out.flush();  
    }  
      
    /** 
     * Initialization of the servlet. <br> 
     * 
     * @throws ServletException if an error occurs 
     */  
    public void init() throws ServletException {  
    }  
  
}  

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
    xmlns="http://java.sun.com/xml/ns/javaee" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
    http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
    
    
<servlet>  
    <description>This is the description of my J2EE component</description>  
    <display-name>This is the display name of my J2EE component</display-name>  
    <servlet-name>MyServlet</servlet-name>  
    <servlet-class>xieyuan.MyServlet</servlet-class>  
  </servlet>  
  
  <servlet-mapping>  
    <servlet-name>MyServlet</servlet-name>  
    <url-pattern>/servlet/MyServlet</url-pattern>  
  </servlet-mapping>  
  <welcome-file-list>  
    <welcome-file>index.jsp</welcome-file>  
  </welcome-file-list>  
</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="http://www.mamicode.com/">  
      
    <title>My JSP ‘index.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="http://www.mamicode.com/styles.css">  
    -->  
    <script language="JavaScript" >  
        function reloadImage()  
        {  
           <!--将按钮状态设置为不可用，当图片加载完成触发onload后，按钮状态就为可用了。这样可用避免重复获取-->  
           document.getElementById("btn").disabled=true;  
           <!--第一次连接的时候不会有问题，第二次连接时，假如你后面没有new Date().getTime(),加参数就会连接的时候拿缓存，没有连到服务器。加上时间函数就能保证你每次得到的不是浏览器的缓存。-->  
           document.getElementById("img").src="http://www.mamicode.com/servlet/MyServlet?timestamp="+new Date().getTime();  
         }  
    </script>  
  </head>  
    
  <body>  
     <img src="http://www.mamicode.com/servlet/MyServlet" id="img" onl oad="btn.disabled=false;" /><br/><br/>  
     <input type="button" value="http://www.mamicode.com/换一张图片" onClick="reloadImage()" id="btn" /><br/>  
     <script>document.write("页面最后更新："+document.lastModified)</script>  
  </body>  
</html>