1、书写servlet，获取验证码的数据，并对验证码进行校验
public class ValidateServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
String code = request.getParameter("code");
HttpSession session = request.getSession();
String randStr = (String)session.getAttribute("randStr");
response.setCharacterEncoding("gb2312");
PrintWriter out = response.getWriter();
if(!code.equals(randStr)){
out.println("验证码错误");
}
else{
out.println("验证码正确......");
}
}
}
2、创建登录界面
<%@ page language="java" pageEncoding="gb2312"%>
<html>
<body>
<script type="text/javascript">
function refresh(){
document.getElementById("imgValidate").src="validate.jsp?random="+Math.random();
}
</script>
欢迎登录本系统<BR>
<form name="loginForm" action="ValidateServlet" method="post">
请您输入账号:<input type="text" name="account" /><BR>
请您输入密码: <input type="password" name="password" /><BR>
请输入验证码:<input type="text" name="code" size="10"/>
<img name="imgValidate" id="imgValidate" src="validate.jsp" onclick="refresh()"/><BR>
<input type="submit" value="登录"/>
</form>
</body>
</html>
点击验证码的图片之后会调用validate.jsp生成验证码，但是，在这个过程中会传递一个随机数，在validate.jsp中对数据进行模糊处理，并将数据存储在session中。
3、创建生成验证码图片的jsp
<%@ page language="java"
import="java.awt.*"
import="java.awt.image.BufferedImage"
import="java.util.*"
import="javax.imageio.ImageIO"
pageEncoding="gb2312"%>
<%
response.setHeader("Cache-Control","no-cache");
// 在内存中创建图象
int width = 60, height = 20;
BufferedImage image = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
//获取画笔
Graphics g = image.getGraphics();
//设定背景色
g.setColor(new Color(200, 200, 200));
g.fillRect(0, 0, width, height);
//取随机产生的验证码(4位数字)
Random rnd = new Random();
int randNum = rnd.nextInt(8999) + 1000;
String randStr = String.valueOf(randNum);
//将验证码存入session
session.setAttribute("randStr", randStr);
//将验证码显示到图象中
g.setColor(Color.black);
g.setFont(new Font("", Font.PLAIN, 20));
g.drawString(randStr, 10, 17);
// 随机产生100个干扰点，使图象中的验证码不易被其他程序探测到
for (int i = 0; i < 100; i++){
int x = rnd.nextInt(width);
int y = rnd.nextInt(height);
g.drawOval(x, y, 1, 1);
}
// 输出图象到页面
ImageIO.write(image, "JPEG", response.getOutputStream());
out.clear();
out = pageContext.pushBody();
%>
4、在web.xml中配置servlet
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>yanzheng</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>ValidateServlet</servlet-name>
<servlet-class>pers.zhb.test.ValidateServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ValidateServlet</servlet-name>
<url-pattern>/ValidateServlet</url-pattern>
</servlet-mapping>
</web-app>