分析

生成图片实现类

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

代码实现

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

index.jsp

pageEncoding="UTF-8"%>

>

Insert title heretitle>

function reloadCode() {

//传个时间参数，防止缓存

var time = new Date().getTime();

document.getElementById("imageCode").src="/ImageServlet?d="+time;

}

script>

head>

/LoginServlet" method="post">

验证码：

/ImageServlet" alt="验证码" />

看不清楚a>

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

ImageServletservlet-name>

com.liuyanzhao.ImageServletservlet-class>

servlet>

ImageServletservlet-name>

/ImageServleturl-pattern>

servlet-mapping>

LoginServletservlet-name>

com.liuyanzhao.LoginServletservlet-class>

servlet>

LoginServletservlet-name>

/LoginServleturl-pattern>

servlet-mapping>

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