jsp+servlet实现验证码功能

验证码的功能大多数人可能不都理解，但几乎每个安全网站都会有。验证码是用来防止非人为因素操作的行为，例如一个黑客要黑一个网站，怎么弄呢？最简单的思路当然是造成其网路拥堵直至系统瘫痪掉。如果没有验证码，那么我就可以在注册页面，写一个程序，只有注册表单，不断更换主键或不可重复的内容，不停的提交。那这样每秒可以注册几万次都有可能，这样服务器就大量负载，很容易就瘫痪并死掉。而达到这样的目的并不困难。

增加验证码之后，就不是机器人能识别的了，必须是人在操作系统，由于是图片形式的，而且歪歪斜斜乱七八糟，而现阶段图形模式识别技术还没做到能够识别验证码的程度，所以加上验证码就相对安全了很多。在软件开发中难免会遇到这样的情况，客户压根不知道验证码用来干什么的，但一定要加不可。为什么要加？因为大家都有。没法子总要加上才显得自己专业，其实这个东西很容易加，就是用数字或字母做模板用swing的图形API，画出一个图片出来。完整的逻辑和代码如下：

<img id="validateCodeId" src="validateCodeServlet"                                    onclick="flushValidateCode(this);" title='看不清,点击刷新'                                    style="cursor: pointer;" />

//刷新验证码flushValidateCode = function(obj) {obj.src  ='validateCodeServlet?d='+new Date();}

请求的URL是validateCodeServlet，后面参数d=new Date()是保证每次点击刷新的时候URL都不一样，否则会不刷新。别的地方也使用Math.rand();这样的办法取得一个随机数，这样也是可以的。

web.xml这样来配置servlet的映射信息。

  <servlet>    <servlet-name>validateCode</servlet-name>    <servlet-class>com.xzfy.mainpage.web.action.ValidateCodeServlet</servlet-class>  </servlet>    <servlet-mapping>        <servlet-name>validateCode</servlet-name>        <url-pattern>/validateCodeServlet</url-pattern>    </servlet-mapping>

ValidateCodeServlet

package com.xzfy.mainpage.web.action;import java.awt.Color;import java.awt.Font;import java.awt.Graphics;import java.awt.image.BufferedImage;import java.io.IOException;import java.io.PrintWriter;import java.util.Random;import javax.imageio.ImageIO;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;import org.apache.commons.io.output.ByteArrayOutputStream;public class ValidateCodeServlet extends HttpServlet {/** * Constructor of the object. */public ValidateCodeServlet() {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");response.setHeader("Pragma", "No-cache");response.setHeader("Cache-Control", "no-cache");response.setDateHeader("Expires", 0);HttpSession session = request.getSession();int width = 60, height = 20;BufferedImage image = new BufferedImage(width, height,BufferedImage.TYPE_INT_RGB);Graphics g = image.getGraphics();Random random = new Random();g.setColor(getRandColor(200, 250));g.fillRect(0, 0, width, height);g.setFont(new Font("Times New Roman", Font.PLAIN, 18));g.setColor(getRandColor(160, 200));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);}String sRand = "";for (int i = 0; i < 4; i++) {String rand = String.valueOf(random.nextInt(10));sRand += rand;g.setColor(new Color(20 + random.nextInt(110), 20 + random.nextInt(110), 20 + random.nextInt(110)));// 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, 16);}session.setAttribute("rand", sRand);g.dispose();ServletOutputStream responseOutputStream = response.getOutputStream();ImageIO.write(image, "JPEG", responseOutputStream);responseOutputStream.flush();responseOutputStream.close();}/** * 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}Color getRandColor(int fc, int bc) {// 给定范围获得随机颜色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);}}

效果如下：