工作中使用的java jsp实现的登录验证码。代码记录如下：
1.登录主页面（login.jsp）
class="java" name="code"><%@ 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>登录</title>
<script type="text/javascript">
function refresh() {
//IE存在缓存,需要new Date()实现更换路径的作用
document.getElementById("image").src="../login/image.jsp?"+new Date();
}
</script>
</head>
<body>
<form action="../login/check.jsp" method="post" id="loginForm" name="loginForm">
用户名：<input type="text" name="userName">
密码：<input type="password" name="userPwd">
验证码：<input type="text" name="code" maxlength="4">
<img id="image" border="0" onclick="refresh()" src="../login/image.jsp" title="点击更换图片">
<input type="submit" value="登录">
</form>
</body>
</html>
?2. 验证码生成jsp(image.jsp)
<%@page import="javax.imageio.ImageIO"%>
<%@page import="java.awt.Font"%>
<%@page import="java.awt.Graphics"%>
<%@page import="java.awt.image.BufferedImage"%>
<%@page import="java.util.Random"%>
<%@page import="java.awt.Color"%>
<%@ page language="java" contentType="image/JPEG; charset=UTF-8"
pageEncoding="UTF-8"%>
<%!
//获取随机颜色
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);
}
%>
<%
//设置页面不缓存
response.setHeader("Pragma", "No-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0);
//在内存中创建图像
int width = 60;
int height = 20;
BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
//获取图形上下文
Graphics g = image.getGraphics();
//随机类
Random random = new Random();
//设定背景
g.setColor(getRandColor(200, 250));
g.fillRect(0, 0, width, height);
//设定字体
g.setFont(new Font("Times New Roman",Font.PLAIN,18));
//随机产生干扰线
g.setColor(getRandColor(160, 200));
for (int i = 0; i < 100; 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);
}
//随机产生4位验证码
String[] codes = {"2","3","4","5","6","7","8","9","A","B","C","D","E","F","G","H","J","K","L","M","N","P","Q","R","S","T","U","V","W","X","Y","Z"};
String code = "";
for(int i=0;i<4;i++){
String str = codes[random.nextInt(codes.length)];
code += str;
// 将认证码显示到图象中
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(str, 13 * i + 6, 16);
}
// 将认证码存入SESSION
session.setAttribute("code", code);
// 图象生效
g.dispose();
// 输出图象到页面
ImageIO.write(image, "JPEG", response.getOutputStream());
//加上下面代码,运行时才不会出现java.lang.IllegalStateException: getOutputStream() has already been called ..........等异常
response.getOutputStream().flush();
response.getOutputStream().close();
response.flushBuffer();
out.clear();
out = pageContext.pushBody();
%>
?3. 验证码检查页面（check.jsp：检查验证码是否输入正确）
<%@ 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>验证</title>
<script type="text/javascript">
function same(){
loginForm.action = "login/login_login";
loginForm.submit();
}
function different(){
alert("请输入正确的验证码");
location.href = "login.jsp";
}
</script>
</head>
<body>
<%
String userName = request.getParameter("userName");
String password = request.getParameter("userPwd");
%>
<form id="loginForm" name="loginForm" method="post">
<input type="hidden" id="userName" value=<%=userName %> name="user.userName">
<input type="hidden" id="userPwd" value=<%=password %> name="user.userPwd">
</form>
<%
String rand = session.getAttribute("code").toString();
String input = request.getParameter("code");
if(rand.equals(input)){
out.println("<script language='javascript'>same();</script>");
}else{
out.print("<script language='javascript'>different();</script>");
}
%>
</body>
</html>
?
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