驗證碼大家都知道，它的作用也不用我多說了吧。如果不太清楚請參見百度百科中的解釋，一般驗證碼的生成就是隨機產生字符（數字、字母或者漢字等），然後將這些生成的字符繪製成一張圖片，再在圖片上加上一些干擾元素，如各種線條之類的。好了廢話不多說一起往下看：
簡單的登錄頁面（代碼並不完整，只有驗證碼部分）
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>驗證碼</title> <script type="text/javascript"> <span style="white-space:pre" data-filtered="filtered"></span><span style="white-space:pre"> </span> //刷新驗證碼的js函數<span style="white-space:pre"> </span>function changeCode() { <span style="white-space:pre"> </span>var imgNode = document.getElementById("vimg"); <span style="white-space:pre"> </span>//重新加載驗證碼，達到刷新的目的<span style="white-space:pre"> </span>imgNode.src = "servlet/AuthImageServlet?t=" + Math.random(); // 防止瀏覽器緩存的問題<span style="white-space:pre"> </span>} </script> </head> <body> <form action="checkServlet" method="post"> <label>輸入驗證碼</label><br/> <input type="text" name="randomCode"/><img id="vimg" onclick="changeCode();" src="servlet/AuthImageServlet"><br/> <input type="submit" value="submit"> </form> </body> </html>通過session.getAttribute("rand")，獲得生成的驗證碼，然後跟用戶輸入的進行比較，再根據比較結果做相應的處理。
通過servlet生成驗證碼：
package com.util.servlet; 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; public class AuthImageServlet extends HttpServlet { private static final String CONTENT_TYPE = "text/html; charset=gb2312"; //設置字母的大小,大小private Font mFont = new Font("Times New Roman", Font.PLAIN, 17); public void init() throws ServletException { super.init(); } 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); } public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setHeader("Pragma","No-cache"); response.setHeader("Cache-Control","no-cache"); response.setDateHeader("Expires", 0); //表明生成的響應是圖片response.setContentType("image/jpeg"); int width=100, height=18; 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(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)); //畫隨機線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); } //從另一方向畫隨機線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); } //生成隨機數,並將隨機數字轉換為字母String sRand=""; for (int i=0;i<6;i++) { int itmp = random.nextInt(26) + 65; char ctmp = (char)itmp; sRand += String.valueOf(ctmp); g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110))); g.drawString(String.valueOf(ctmp),15*i+10,16); } HttpSession session = request.getSession(true); session.setAttribute("rand",sRand); g.dispose(); ImageIO.write(image, "JPEG", response.getOutputStream()); } }web.xml中的servlet配置信息：
<?xml version="1.0" encoding="UTF-8"?> <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> <servlet> <servlet-name>AuthImageServlet</servlet-name> <servlet-class>com.util.servlet.AuthImageServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>AuthImageServlet</servlet-name> <url-pattern>/servlet/AuthImageServlet</url-pattern> </servlet-mapping> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> </web-app>
就這樣驗證碼的功能就實現了，很簡單、很實用。當然還有更加美觀，更加嚴密的方式，有興趣的朋友可以深入研究。這裡就跟大家分享一個比較簡單的方式。歡迎各位批評指正。
以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持武林網。