验证码的作用：
验证码是Completely Automated Public Turing test to tell Computers and Humans Apart(全自动区分计算机和人类的图灵测试)的缩写，是一种区分用户是计算机还是人的公共全自动程序，可以防止：恶意破解密码、刷票、论坛灌水、有效防止某个黑客对某一特定注册用户，用特定程序暴力破解方式进行不断的登录尝试。实际上验证码是现在很多网站通行的方式，我们利用比较简易的方式实现了这个功能。
第一代：标准验证码
这一代验证码是即是我们常见的图形验证码、语音验证码，基于机器难以处理复杂的计算机视觉及语音识别问题，而人类却可以轻松的识别来区分人类及机器。这一代验证码初步利用了人类知识容易解答，而计算机难以解答的机制进行人机判断。下面这种验证码就是第一代
Java 中生成验证码，一个.java就可以了
ValidateCodeServlet.java
package com.hpe.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.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse; @WebServlet("/ValidateCodeServlet")
public class ValidateCodeServlet extends HttpServlet {
private static final long serialVersionUID = 1L; public ValidateCodeServlet() {
super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { doPost(request, response);
} protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { // 响应头信息
response.setHeader("Pragma", "No-Cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expries", 0); // 随机数生成类
Random random = new Random(); // 定义验证码的位数
int size = 5; // 定义变量保存生成的验证码
String vCode = "";
char c;
// 产生验证码
for (int i = 0; i < size; i++) {
// 产生一个26以内的随机整数
int number = random.nextInt(26);
// 如果生成的是偶数，则随机生成一个数字
if (number % 2 == 0) {
c = (char) ('0' + (char) ((int) (Math.random() * 10)));
// 如果生成的是奇数，则随机生成一个字母
} else {
c = (char) ((char) ((int) (Math.random() * 26)) + 'A');
}
vCode = vCode + c;
} // 保存生成的5位验证码
request.getSession().setAttribute("vCode", vCode); // 验证码图片的生成
// 定义图片的宽度和高度
int width = (int) Math.ceil(size * 20);
int height = 50;
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
// 获取图片的上下文
Graphics gr = image.getGraphics();
// 设定图片背景颜色
gr.setColor(Color.WHITE);
gr.fillRect(0, 0, width, height);
// 设定图片边框
gr.setColor(Color.GRAY);
gr.drawRect(0, 0, width - 1, height - 1);
// 画十条干扰线
for (int i = 0; i < 5; i++) {
int x1 = random.nextInt(width);
int y1 = random.nextInt(height);
int x2 = random.nextInt(width);
int y2 = random.nextInt(height);
gr.setColor(randomColor());
gr.drawLine(x1, y1, x2, y2);
}
// 设置字体，画验证码
gr.setColor(randomColor());
gr.setFont(randomFont());
gr.drawString(vCode, 10, 22);
// 图像生效
gr.dispose();
// 输出到页面
ImageIO.write(image, "JPEG", response.getOutputStream()); } // 生成随机的颜色
private Color randomColor() {
int red = r.nextInt(150);
int green = r.nextInt(150);
int blue = r.nextInt(150);
return new Color(red, green, blue);
} private String[] fontNames = { "宋体", "华文楷体", "黑体", "微软雅黑", "楷体_GB2312" };
private Random r = new Random(); // 生成随机的字体
private Font randomFont() {
int index = r.nextInt(fontNames.length);
String fontName = fontNames[index];// 生成随机的字体名称
int style = r.nextInt(4);
int size = r.nextInt(3) + 24; // 生成随机字号, 24 ~ 28
return new Font(fontName, style, size);
}
}
直接运行Java生成的结果：
在jsp网页上显示的效果：
jsp代码：
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta http-equiv="Pragma" content="no-cache">
<meta http-equiv="Cache-Control" content="no-cache">
<meta http-equiv="Expires" content="0">
<title>login</title>
<link href="css/login.css" type="text/css" rel="stylesheet">
<script type="text/javascript">
function $(id){
return document.getElementById(id);
}
function changeCode(){
$("code").src = "ValidateCodeServlet?a="+new Date();
}
</script>
</head>
<body> <div class="login">
<div class="message">欢迎登录</div>
<hr class="hr15">
<div id="darkbannerwrap"></div> <form method="post">
<input name="action" value="login" type="hidden"> <input
name="username" placeholder="用户名" required="" type="text">
<hr class="hr15">
<input name="password" placeholder="密码" required="" type="password">
<hr class="hr15">
<input name="check_code" placeholder="验证码" required="" type="text"
style="width: 30%;"> <img class="img_code"
src="ValidateCodeServlet" id="code" /> <a class="a_code"
href="javascript:changeCode()">换一张</a>
<hr class="hr15"> </form>
</div>
</body>
</html>