JSP生成验证码
本例运行在Tomact服务器下一切正常:
生成验证码:
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@page import="java.awt.Color"%>
<%@page import="java.awt.image.BufferedImage"%>
<%@page import="java.awt.Graphics"%>
<%@page import="java.awt.Font"%>
<%@page import="javax.imageio.ImageIO"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'CreateCaptcha.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<%!
Color getRandColor(int fc,int bc){//给定范围获得随机颜色
Random random=new Random();
if(fc>255){
fc=255;
}else 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();
//生成随机类
Random random=new Random();
//设定背景色
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));
//画边框
//g.setColor(new Color(160,200));
//g.drawRect(0,0,width-1,height-1);
//随机产生155条干扰线,使图像中的验证码不易被其他程序探测到
g.setColor(getRandColor(160,200));
for(int i=0;i<155;i++){
int x=random.nextInt(width);
int y=random.nextInt(height);
int x1=random.nextInt(12);
int y1=random.nextInt(12);
g.drawLine(x,y,x+x1,y+y1);
}
//随机产生的验证码(4位数)
String sRand="";
for(int i=0;i<4;i++){
String rand=String.valueOf(random.nextInt(10));
sRand+=rand;
//将验证码显示到图像中
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,可能是因为种子太近,所以只能直接生成
g.drawString(rand,13*i+6,16);
}
//将谁码存入session中
session.setAttribute("rand",sRand);
//图像生效
g.dispose();
//输出图像到页面
ImageIO.write(image,"JPEG",response.getOutputStream());
%>
</body>
</html>
测试页面:
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'TestCaptcha.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<%
String captcha=(String)session.getAttribute("rand");
String checkCaptcha=(String)request.getParameter("checkCaptcha");
if(captcha!=null&&(checkCaptcha.equals(captcha))){
session.setAttribute("captcha",captcha);%>
验证成功!!!
<%}else{%>
<form action="TestCaptcha.jsp" method="get">
验证码: <img alt="验证码" src="CreateCaptcha.jsp"><br/>
验证吗: <input type="text" name="checkCaptcha"/><br/>
<input type="submit" value="测试验证码"/>
<%} %>
</form>
</body>
</html>
运行报: java.lang.IllegalStateException: getOutputStream() has already been called for this response异常
解决方案：在程序的最后添加：
out.clear();
out = pageContext.pushBody();
在Resin服务器中,图片显示不了 需注释掉上面两句,在设置页面不缓存上一行加入 out.clear();及可得到解决