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：
[html]
<img id="validateCodeId" src="validateCodeServlet"
onclick="flushValidateCode(this);" title='看不清,点击刷新'
style="cursor: po
inter;" />
[
javascript]
//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。
[html]
<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
[java]
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
}
www.atcpu.com 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：
