package com.servlet;

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.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.image.codec.jpeg.JPEGCodec;

import com.sun.image.codec.jpeg.JPEGImageEncoder;

public class IdentityServlet extends HttpServlet {

    public static final char[] chars={'','','','','','','','','A'};//自定义验证码池

    public static Random random=new Random();　　//随机数

    public static String getRandomString(){　　//获取6位随机数，放在图片里

        StringBuffer buffer=new StringBuffer();

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

            buffer.append(chars[random.nextInt(chars.length)]);

        }

        return buffer.toString();

    }

    public static Color getRandomColor(){　　//获取随机的颜色

        return new Color(random.nextInt(), random.nextInt(), random.nextInt());

    }

    public static Color getReverseColor(Color c){　　//返回某颜色的反色

        return new Color( - c.getRed(),  - c.getGreen(),  - c.getBlue());

    }

    /**

     * Constructor of the object.

     */

    public IdentityServlet() {

        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 {

        response.setContentType("image/jpeg");　　//设置输出类型

        String randomString = getRandomString();　　//随机字符串

        request.getSession(true).setAttribute("randomString", randomString);//放到session里

        int width=;　　//图片宽度

        int height=;　　//图片高度

        Color color=getRandomColor();　　//随机颜色，用于背景色

        Color reverse=getReverseColor(color);//反色，用于前景色

        //创建一个彩色图片

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

        Graphics2D g=bi.createGraphics();　　//绘图对象

        g.setFont(new Font(Font.SANS_SERIF,Font.BOLD,));//设置字体

        g.setColor(color);//设置颜色

        g.fillRect(, , width, height);//绘制背景

        g.setColor(reverse);

        g.drawString(randomString, , );//绘制随机字符

        for(int i=,n=random.nextInt();i<n;i++){　　//画最多100个噪音点

            g.drawRect(random.nextInt(width), random.nextInt(height), , );

        }

        ServletOutputStream out= response.getOutputStream();//转成JPEG格式

        JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(out);//编码器

        encoder.encode(bi);　　//对图片进行编码

        out.flush();　　//输出到客户端

    }

    /**

     * 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 {

        doGet(request, response);

    }

    /**

     * Initialization of the servlet. <br>

     *

     * @throws ServletException if an error occurs

     */

    public void init() throws ServletException {

        // Put your code here

    }

}

<?xml version="1.0" encoding="UTF-8"?>

<web-app version="3.0"

    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_3_0.xsd">

  <display-name></display-name>

  <servlet>

    <servlet-name>IdentityServlet</servlet-name>

    <servlet-class>com.servlet.IdentityServlet</servlet-class>

  </servlet>

  <servlet-mapping>

    <servlet-name>IdentityServlet</servlet-name>

    <url-pattern>/servlet/IdentityServlet</url-pattern>

  </servlet-mapping>

  <welcome-file-list>

    <welcome-file>index.jsp</welcome-file>

  </welcome-file-list>

</web-app>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<title>Insert title here</title>

<script type="text/javascript">

function reloadImage(){

    document.getElementById('btn').disabled=true;

    document.getElementById('identity').src='servlet/IdentityServlet?ts='+new Date().getTime();

}

</script>

</head>

<body>

<img src="servlet/IdentityServlet" id="identity" onload="btn.disabled=false;" />

<input type=button value="换个图片" onclick="reloadImage()" id="btn">

</body>

</html>