用java来实现验证码功能。

昨天在网上看到了一篇关于验证码的文章，很不错，但是有些不尽人意的地方，比如没有考虑到前端传过来的验证码如果是小写的话，那么做验证的时候就会出现错误，

因为java是严格区分大小写的，还有就是验证码会重叠在一起的情况没有考虑到，再者验证码看不清刷新的功能没有做出来

在此我做下修改：

首先需要导入ValidateCode.jar包

 package com.wqy.ValidateCode;

 import java.io.IOException;

 import javax.imageio.ImageIO;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 import cn.dsna.util.images.ValidateCode;

 public class ValidateCode1 extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         //控制不要缓存
         response.setHeader("Expires", "-1");
         response.setHeader("Cache-Control", "no-cache");
         response.setHeader("Pragma", "no-cache");
         int width=120;//宽度
         int height=25;//高度
         int codeCount=4;//验证码的个数
         int lineCount=9;//干扰线的个数
         //设置验证码
         ValidateCode vc = new ValidateCode(width, height, codeCount, lineCount);
                 //ValidateCode(120,25,4,9);
         String code = vc.getCode();
         //将验证码存放到Attribute域中
         request.getSession().setAttribute("code", code);
         //输出
         ImageIO.write(vc.getBuffImg(), "jpg", response.getOutputStream());

     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
             doGet(request,response);
     }

 }

下面是html代码：

<%@ page language="java" import="java.util.*" pageEncoding="GBK"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<html>
  <head>
    <title>验证码</title>
  </head>

  <body>
      <form action="${pageContext.request.contextPath}/servlet/LoginServlet" method="post">
      用户名:<input type="text" name="username"/></br>
      密码:<input type="password" name="password"/></br>
      验证码:<input type="text" name="captcha" size="4">
      <img src="${pageContext.request.contextPath}/servlet/ValidateCode1"  id="CreateCheckCode" onclick="this.src=this.src+'?'" width="120" height="25">
      <a href="javascript:CreateCheckCode.onclick()">看不清，换一张</a></br>
      <input type="submit" value="登录">
      </form>
  </body>
</html>

后台验证的servlet代码：

 package com.wqy.ValidateCode;

 import java.io.IOException;

 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 public class LoginServlet extends HttpServlet {
     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         //获取前端传来的验证码
         String name = request.getParameter("captcha");
         //从Attribute域中获取存放的验证码
         String code = (String)request.getSession().getAttribute("code");
         //前后端验证码做比较。（验证码.toLowerCase是让它忽略大小写，这样在前端做验证的时候就不会因为大小写问题引发异常）
         if(code.toLowerCase().equals(name.toLowerCase())){
             System.out.println("验证码正确");
         }
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         doGet(request, response);
     }

 }

最终显示结果：