Servlet 实现验证码

摘要: 分析生成图片实现类ImageServlet 类① 定义BufferedImage 对象② 获得 Graphics 对象③ 通过 Random 产生随机验证码信息④ 使用 Graphics 绘

分析

生成图片实现类

ImageServlet 类

① 定义BufferedImage 对象

② 获得 Graphics 对象

③ 通过 Random 产生随机验证码信息

④ 使用 Graphics 绘制图片

⑤ 记录验证码信息到 session 中

⑥ 使用 ImageIO 输出图片

1、新建 web 项目 CheckCode，在 WebContent 下新建 index.jsp

index.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title heretitle>
<script type="text/javascript">
function reloadCode() {
//传个时间参数，防止缓存
var time = new Date().getTime();
document.getElementById("imageCode").src="<%=request.getContextPath()%>/ImageServlet?d="+time;
}
script>
head>
<body>
<form action="<%=request.getContextPath()%>/LoginServlet" method="post">
验证码：<input type="text" name="checkcode" />
<img id="imageCode" src="<%=request.getContextPath()%>/ImageServlet" alt="验证码" />
<a href="javascript:reloadCode();">看不清楚a> <br />
<input type="submit" value="提交"/>
form>
body>
html>

2、在 src 下新建 com.liuyanzhao 包，然后分别新建用于动态画图的 ImageServlet 类和用于判断验证码是否正确的 LoginServlet 类

ImageServlet.java

package com.liuyanzhao;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/*
* @author LiuYanzhao
*/
public class ImageServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
BufferedImage bi = new BufferedImage(68, 22, BufferedImage.TYPE_INT_RGB);
Graphics g = bi.getGraphics();
Color c = new Color(200,155,255);
g.setColor(c);
g.fillRect(0, 0, 68, 22);
char[] ch = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".toCharArray();
Random r = new Random();
int len = ch.length,index;
StringBuffer sb = new StringBuffer();
for(int i=0;i<4;i++) {
index = r.nextInt(len);
g.setColor(new Color(r.nextInt(88),r.nextInt(188),r.nextInt(255)));
g.drawString(ch[index]+"", (i*15)+3, 18);
sb.append(ch[index]);
}
request.getSession().setAttribute("piccode", sb.toString());
ImageIO.write(bi, "JPG", response.getOutputStream());
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}

LoginServlet.java

package com.liuyanzhao;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/*
* @author LiuYanzhao
*/
public class LoginServlet extends HttpServlet{
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String piccode = (String)request.getSession().getAttribute("piccode");
String checkcode = request.getParameter("checkcode");
checkcode = checkcode.toUpperCase();//不区分大小写
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
if(piccode.equals(checkcode)) {
out.println("验证码输入正确");
} else {
out.println("验证码输入错误");
}
out.flush();
out.close();
}
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
}

3、在 web.xml 里添加 Servlet 映射

4、运行 Tomcat 服务器，打开浏览器，访问 http://localhost:8080/CheckCode

效果如下

验证码不区分大小写，点击 “看不清楚”可以更换