Java Web：使用Servlet生成网页随机图片验证码

     最近在学习Java Web开发，做了一个生成网页随机图片验证码的例子，在此记录。

     一、新建Servlet项目：

         在MyEclipse中新建Servlet项目，一步步操作就OK，在此不再赘述。建好之后文件目录树如下图：

    二、源代码实现：

         （1）java代码：

package com.zdt.identity;

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 Servlet1 extends HttpServlet {

	
	//随机字符集合
		public static final char[] CHARS = {'0','1','2','3','4','5','6',
			'7','8','9','A','B','C','D','E','F','G','H','I','J','K','L',
			'M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
		//随机数
		public static Random random = new Random();
		
		//获取6位随机数
		public static String getRandomString() {
			//字符串缓存
			StringBuffer strBuffer = new StringBuffer();
			//循环从字符集中随机取出6个字符
			for (int i = 0; i < 6; i++) {
				strBuffer.append(CHARS[random.nextInt(CHARS.length)]);
			}
			return strBuffer.toString();
		}
		
		//获取随机颜色
		public static Color getRandomColor() {
			return new Color(random.nextInt(255), random.nextInt(255),
					random.nextInt(255));
		}
		
		//获取某一颜色的反色
		public static Color getReverseColor(Color c) {
			return new Color(255 - c.getRed(), 255 - c.getGreen(), 
					255 - c.getBlue());
		}
	/**
	 * Constructor of the object.
	 */
	public Servlet1() {
		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 {


		//设置输出的类型，此处为图片
		response.setContentType("image/jpeg");
		//获取随机字符串
		String randomString = getRandomString();
		//把随机字符串绑定到当前会话
		request.getSession(true).setAttribute("randomString", randomString);
		
		int width = 100;//图片宽度
		int height = 30;//图片高度
		
		//获取一种随机颜色
		Color color = getRandomColor();
		//获取上述颜色的反色
		Color reverseColor = getReverseColor(color);
		
		//根据宽度和高度，创建一个彩色图片
		BufferedImage bi = new BufferedImage(width, height, 
				BufferedImage.TYPE_INT_BGR);
		
		//获取绘图对象
		Graphics2D graphics2d = bi.createGraphics();
		//设置字体
		graphics2d.setFont(new Font(Font.SANS_SERIF, 
				Font.BOLD, 16));
		//设置颜色
		graphics2d.setColor(color);
		//绘制背景
		graphics2d.fillRect(0, 0, width, height);
		//设置背景颜色，与字符颜色相反
		graphics2d.setColor(reverseColor);
		//绘制随机字符
		graphics2d.drawString(randomString, 18, 20);
		//绘制随机噪音点，最多绘制100个
		for (int i = 0, n = random.nextInt(100); i < n; i++) {
			graphics2d.drawRect(random.nextInt(width), 
					random.nextInt(height), 1, 1);
		}
		
		//响应的输出流
		ServletOutputStream servletOutputStream = response.getOutputStream();
		//转换成JPEG格式
		JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(servletOutputStream);
		//对图片编码
		encoder.encode(bi);
		//输出到客户端
		servletOutputStream.flush();
	
	}

	/**
	 * 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 {
		
	}

	/**
	 * Initialization of the servlet. <br>
	 *
	 * @throws ServletException if an error occurs
	 */
	public void init() throws ServletException {
		// Put your code here
	}

}

（2）写web.xml配置文件，主要代码如下：

<servlet>
		<servlet-name>Servlet1</servlet-name>
		<display-name>This is the display name of my J2EE component</display-name>
		<description>This is the description of my J2EE component</description>
		<servlet-class>com.zdt.identity.Servlet1</servlet-class>
	</servlet>

<servlet-mapping>
		<servlet-name>Servlet1</servlet-name>
		<url-pattern>/servlet/Servlet1</url-pattern>
	</servlet-mapping>

<!DOCTYPE html>
<html>
  <head>
    <title>identity.html</title>
	
    <meta name="keywords" content="keyword1,keyword2,keyword3">
    <meta name="description" content="this is my page">
    <meta name="content-type" content="text/html; charset=GBK">
    
    <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->

  </head>
  
  <script>
  function reloadImage() {
      document.getElementById('btn').disabled = true;
      document.getElementById('Servlet1').src = 'servlet/Servlet1?ts='
       + new Date().getTime();
  }
  </script>
  
  <body>
    This is my HTML page. <br>
    <img alt="" src="servlet/Servlet1" id="Servlet1"
    onload="btn.disabled = false;" />
    <input type=button value="换个图片" onclick="reloadImage()" id="btn">
    
  </body>
</html>

    安装Tomcat并部署成windows服务的教程：http://www.blogjava.net/lushengdi/archive/2010/07/01/324952.html

     找到Tomcat的安装目录，在webapps目录下新建一个文件夹，命名servletTest，把项目编译后的WebRoot文件夹下的所有文件复制到servletTest文件夹中，Tomcat会自动加载项目。

   四、结果演示

   在浏览器地址栏中输入：http://localhost:8080/servletTest/identity.html，回车，结果如下图：

点击“换个图片”按钮，图片就会变化