用servlet生成验证码

package com.work.core.image;



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;



import org.apache.commons.logging.Log;

import org.apache.commons.logging.LogFactory;



/**

 * @author wangmj

 * 生成随机的验证码！防止暴利破解。

 */

public class AuthImage extends HttpServlet {

	private static Log log = LogFactory.getLog(AuthImage.class);

	/**

	 * 

	 */

	private static final long serialVersionUID = 8165458985542870320L;

//设置图形验证码中的字符串的字体的大小

	private Font mFont = new Font("Arial Black", Font.PLAIN, 16);



	public void init() throws ServletException {

		super.init();

	}



	/**

	 * 生成随机颜色

	 * @param fc

	 * @param bc

	 * @return

	 */

	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);

	}



	/* (non-Javadoc)

	 * @see javax.servlet.http.HttpServlet#service(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)

	 */

	public void service(HttpServletRequest request, HttpServletResponse response)

			throws ServletException, IOException {

		//生成服务器相应的service方法

		//阻止生成的页面内容被缓存，保证每次重新生成随机验证码

		response.setHeader("Pragma", "No-cache");

		response.setHeader("Cache-Control", "no-cache");

		response.setDateHeader("Expires", 0);

		response.setContentType("image/jpeg");

//指定图形验证码图片的大小；

		int width = 80;//宽度

		int height = 20;//高度

		

		BufferedImage image = new BufferedImage(width, height,

				BufferedImage.TYPE_INT_RGB);



//		准备在图片中绘制内容

		Graphics g = image.getGraphics();

		Random random = new Random();

		g.setColor(getRandColor(200, 250));

		g.fillRect(1, 1, width - 1, height - 1);

		g.setColor(new Color(102, 102, 102));

		g.drawRect(0, 0, width - 1, height - 1);

		g.setFont(mFont);

		

		g.setColor(getRandColor(160, 200));

		//生成随机线条

		for (int i = 0; i < 155; i++) {

			int x = random.nextInt(width - 1);

			int y = random.nextInt(height - 1);

			int xl = random.nextInt(6) + 1;

			int yl = random.nextInt(12) + 1;

			g.drawLine(x, y, x + xl, y + yl);

		}

		for (int i = 0; i < 70; i++) {

			int x = random.nextInt(width - 1);

			int y = random.nextInt(height - 1);

			int xl = random.nextInt(12) + 1;

			int yl = random.nextInt(6) + 1;

			g.drawLine(x, y, x - xl, y - yl);

		}



		String sRand = "";

		//生成随机的字符串并加入到图片中

		int LEN = 2; //控制随机码的长度

		for (int i = 0; i < LEN; 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);

		log.debug("随机生成的字符串为"+sRand);

		//将其自动转换为小写。也就是说用户在输入验证码的时候，不需要区分大小写，方便输入。

		session.setAttribute("randomImageStr", sRand.toLowerCase());

		log.debug("从session中取出来"+session.getAttribute("randomImageStr"));

		g.dispose();

		ImageIO.write(image, "JPEG", response.getOutputStream());

	}



	/**

	 * 随机生成字符串

	 * @return

	 */

	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 String.valueOf(itmp);

		}

	}

}

在web.xml中配置这个servlet

<servlet>
<servlet-name>authImage</servlet-name>
<servlet-class>com.work.core.image.AuthImage</servlet-class>
</servlet>

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

<img src="${pageContext.request.contextPath}/authImage" id="authImage" />