驗證碼的功能大多數人可能不都理解，但幾乎每個安全網站都會有。驗證碼是用來防止非人為因素操作的行為，例如一個黑客要黑一個網站，怎麼弄呢？最簡單的思路當然是造成其網路擁堵直至系統癱瘓掉。如果沒有驗證碼，那麼我就可以在注冊頁面，寫一個程序，只有注冊表單，不斷更換主鍵或不可重復的內容，不停的提交。那這樣每秒可以注冊幾萬次都有可能，這樣服務器就大量負載，很容易就癱瘓並死掉。而達到這樣的目的並不困難。
增加驗證碼之後，就不是機器人能識別的了，必須是人在操作系統，由於是圖片形式的，而且歪歪斜斜亂七八糟，而現階段圖形模式識別技術還沒做到能夠識別驗證碼的程度，所以加上驗證碼就相對安全了很多。在軟件開發中難免會遇到這樣的情況，客戶壓根不知道驗證碼用來干什麼的，但一定要加不可。為什麼要加？因為大家都有。沒法子總要加上才顯得自己專業，其實這個東西很容易加，就是用數字或字母做模板用swing的圖形API，畫出一個圖片出來。完整的邏輯和代碼如下：
[html]
<img id="validateCodeId" src="validateCodeServlet"
onclick="flushValidateCode(this);" title='看不清,點擊刷新'
style="cursor: pointer;" />
[javascript]
//刷新驗證碼
flushValidateCode = function(obj) {
obj.src ='validateCodeServlet?d='+new Date();
}
請求的URL是validateCodeServlet，後面參數d=new Date()是保證每次點擊刷新的時候URL都不一樣，否則會不刷新。別的地方也使用Math.rand();這樣的辦法取得一個隨機數，這樣也是可以的。
web.xml這樣來配置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)));// 調用函數出來的顏色相同，可能是因為種子太接近，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.2cto.com
Color getRandColor(int fc, int bc) {// 給定范圍獲得隨機顏色
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：
