java生成验证图片

========================jsp==============================

 function changeImg(){ 
   var a=document.getElementById("mySpan"); 
   a.innerHTML='<img align="middle" src="ImageServlet"/>  <a href="#" onclick="changeImg();">看不清，换一张！</a>'; //会复盖“mySpan”位置 
  } 


<td width="350"><div id="kan"  style="text-align:left;">
  <span id="mySpan"><img alt="点击更换验证码" align="middle" title="点击更换验证码"  src="ImageServlet" /><a  href="#" onclick="changeImg();">看不清，换一张！</a> </span> 
  </div></td>
  </tr>

=====================web.xml=================

<servlet> 
    <servlet-name>ImageServlet</servlet-name> 
    <servlet-class>com.e8online2.comm.util.IdentifyingServlet</servlet-class> 
  </servlet> 
   <servlet-mapping> 
    <servlet-name>ImageServlet</servlet-name> 
    <url-pattern>/ImageServlet</url-pattern> 
  </servlet-mapping> 

=======================最后从session中获取原来的验证码与jsp中上传的验证码比较就可以了=================

package com.e8online2.comm.util;


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;

public class IdentifyingServlet extends HttpServlet {

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

		response.setContentType("image/jpeg");

		// 给定范围获得随机颜色
		// 设置页面不缓存
		response.setHeader("Pragma", "No-cache");
		response.setHeader("Cache-Control", "no-cache");
		response.setDateHeader("Expires", 0);

		// 在内存中创建图象
		int width = 60, height = 17;
		BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

		// 获取图形上下文
		Graphics g = image.getGraphics();

		// 生成随机类
		Random random = new Random();

		// 设定背景色
		g.setColor(getRandom(254, 255));
		g.fillRect(0, 0, width, height);

		// 设定字体
		g.setFont(new Font("Cooper Black", Font.PLAIN, 18));

		// 画边框
		// g.setColor(new Color());
		// g.drawRect(0,0,width-1,height-1);

		// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
		g.setColor(getRandom(230, 240));
		for (int i = 0; i < 155; i++) {
			int x = random.nextInt(width);
			int y = random.nextInt(height);
			int xl = random.nextInt(12);
			int yl = random.nextInt(12);
			g.drawLine(x, y, x + xl, y + yl);
		}

		// 取随机产生的认证码(4位数字)
		String sRand = "";
		for (int i = 0; i < 4; i++) {
			String rand = String.valueOf(random.nextInt(10));
			sRand += rand;
			// 将认证码显示到图象中
			g.setColor(new Color(100 + random.nextInt(130), 100 + random.nextInt(130), 100 + random.nextInt(130)));// 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
			g.drawString(rand, 13 * i + 6, 14);
		}

		// 将认证码存入SESSION
		request.getSession().setAttribute("IdentifyingCode", sRand);

		// 图象生效
		g.dispose();

		// 输出图象到页面
		ImageIO.write(image, "JPEG", response.getOutputStream());
	}

	private Color getRandom(int mixValue, int maxValue) {
		Random random = new Random();
		if (mixValue > 255)
			mixValue = 255;
		if (maxValue > 255)
			maxValue = 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);
		int rgb = mixValue + random.nextInt(maxValue - mixValue);
		return new Color(rgb, rgb, rgb);
	}

}