今天在调试项目的时候发现，在提交表单的时候的验证码有问题，问题是这样的：就是通过debug模式查看得知：jsp页面生成的验证码和表单输入的页面输入的一样，但是到后台执行的时候，你会发现他们是不一样的，现在上图看看：
1.这是表单提交的时候:
2.这是后台得到的生成的验证码：
3.这是后台得到输入的验证码：
这样的问题还是头一次出现，以前没遇到过，经过google，baidu，最后得知是这样的：因为加载jsp页面比加载session快一些
那怎么办才能解决这个办法呢，
又经过多次搜索，思考，实践，终于想出了个好办法
1.在jsp页面用js生成验证码并保存在变量中，验证码作为参数传到java(继承了HttpServlet)类
2.根据jsp页面中传过来的验证码画出一个有干扰线或干扰点的图片
3.在WEB-INF/web.xml中配置 servlet
4.在jsp页面调用配置好的servlet，一般是通过<img src="servlet名" id="code"/>调用
5.提交数据之前验证
<form οnsubmit="return validate();"……/>
局部刷新验证码：<a href="#" οnclick="javascript:show();return false;">看不清,换一张！</a>-----return false;很重要啊
下面直接附上我的例子：
截图如下：
代码如下：
1.JAVA类：CodeServlet.java:
package cn.gov.csrc.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.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;public class CodeServlet extends HttpServlet {/*** 产生验证码图片*/public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("image/jpeg");response.setHeader("Cache-Control", "no-cache");response.setHeader("Pragma", "No-cache");response.setDateHeader("Expires", 0L);int width = 80;int height = 30;BufferedImage image = new BufferedImage(width, height, 1);Graphics g = image.getGraphics();Random random = new Random();g.setColor(getRandColor(200, 250));g.fillRect(0, 0, width, height);g.setFont(new Font("Arial", 0, 25));g.setColor(getRandColor(160, 200));for (int i = 0; i < 155; i++) {int x = random.nextInt(width + 100);int y = random.nextInt(height + 100);int xl = random.nextInt(10);int yl = random.nextInt(12);g.drawOval(x, y, x + xl, y + yl);}String code = request.getParameter("code");String sRand = code;for (int i = 0; i < sRand.length(); i++) {String rand = sRand.substring(i, i + 1);g.setColor(new Color(20 + random.nextInt(110), 20 + random.nextInt(110), 20 + random.nextInt(110)));g.drawString(rand, 14 * i + 5, 25);}g.dispose();javax.servlet.ServletOutputStream imageOut = response.getOutputStream();JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(imageOut);encoder.encode(image);}private 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);}}
2.Web.xml文件：
<?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"><display-name></display-name><welcome-file-list><welcome-file>index.jsp</welcome-file></welcome-file-list><servlet><servlet-name>CodeServlet</servlet-name><servlet-class>cn.gov.csrc.servlet.CodeServlet</servlet-class></servlet><servlet-mapping><servlet-name>CodeServlet</servlet-name><url-pattern>/CodeServlet</url-pattern></servlet-mapping>
</web-app>
3.index.jsp：
<%@ 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>验证码测试</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">
<script language="javascript" type="text/javascript">
var code ; //在全局 定义验证码
function createCode(){ code = ""; var codeLength = 5;//验证码的长度 //所有候选组成验证码的字符，可以用中文 var selectChar = new Array(0,1,2,3,4,5,6,7,8,9,'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'); for(var i=0;i<codeLength;i++){ var charIndex = Math.floor(Math.random()*60); code +=selectChar[charIndex]; } return code;
}
function validate (){ var inputCode = document.getElementById("vcode").value.toLowerCase(); if(inputCode.length <=0){ alert("请输入验证码！"); return false; } else if(inputCode != code.toLowerCase()){ alert("验证码输入错误！"); show();//刷新验证码 return false; }else{ alert("^-^ OK"); return true; }
}
function show(){ //显示验证码 document.getElementById("code").src="CodeServlet?code="+createCode();
}
window.onload = function() {//document.οnlοad=show(); show();//页面加载时加载验证码 //这时无论在ie还是在firefox中，js没有加载完，页面的东西是不会被执行的； }
</script>
</head><body><form οnsubmit="return validate();" action="" method="post"><h3>jsp+js+servlet实现验证码</h3><br /> 用户名：<input type="text" name="" /><br /> 请输入验证码： <inputtype="text" id="vcode" style="width: 60;" maxLength="5" /> <imgsrc="" id="code" /> <a href="#" mce_href="#"οnclick="javascript:show();return false;">看不清,换一张!</a><br /> <inputtype="submit" /></form>
</body>
</html>
下载代码请访问：http://www.zuidaima.com/share/1720368578202624.htm
