使用 Servlet 生成图片验证码

最新推荐文章于 2021-04-22 23:11:54 发布

荆轲刺秦

最新推荐文章于 2021-04-22 23:11:54 发布

阅读量636

点赞数

CC 4.0 BY-SA版权

分类专栏： Java web 文章标签： Servlet 图片验证码

本文链接：https://blog.youkuaiyun.com/ai_xao/article/details/79193553

Java web 专栏收录该内容

9 篇文章

订阅专栏

本文介绍了一种基于Java Servlet的图片验证码生成方法，并详细展示了如何实现验证码的生成与校验过程。通过随机生成字符串并将其显示为图片，客户端用户需要输入该字符串以完成验证。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

原理

服务器生成一个包含随机的字符串的图片发给客户端，客户端提交数据时需要填写字符串作为验证。在服务器端，字符串保存在 session 中，当获取到客户端上传的字符串参数时，对比是否相等。
运行结果图：

实现

生成图片验证码的 Servlet 类

package cn.joker.servlet;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
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;

/**
 * Servlet implementation class IdentityServlet
 */
@WebServlet(description = "response生成图片验证码", urlPatterns = { "/IdentityServlet" })
public class IdentityServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    //随机字符
    private static final char[] CHARS = {'2','3','4','5','6','7','8','9','A','B','C','D',
            'E','F','G','H','I','J'};
    //随机数
    private  Random random = new Random();

    /**
     * @see HttpServlet#HttpServlet()
     */
    public IdentityServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        //response.getWriter().append("Served at: ").append(request.getContextPath());
        // 设置输出类型

        response.setContentType("image/jpeg");
        response.setDateHeader("expries", -1);  
        response.setHeader("Cache-Control", "no-cache");  
        response.setHeader("Pragma", "no-cache");  
        // 获取随机字符串
        String randomString = getRandomString();
        //System.out.println(randomString);
        // 放到session 中
        request.getSession(true).setAttribute("randomString", randomString);

        // 图片的宽度、高度
        int width = 100,height=30;
        //用于背景色
        Color color = getRandomColor();
        // 用于前景色
        Color reverse = getReverseColor(color);

        // 创建一个彩色图片
        BufferedImage bi = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
        // 获取绘图对象
        Graphics2D g = bi.createGraphics();
        g.setFont(new Font(Font.SANS_SERIF ,Font.BOLD,16));
        g.setColor(color);
        g.fillRect(0, 0, width, height);
        g.setColor(reverse);
        g.drawString(randomString, 18, 20);
        // 绘制噪声点
        for(int i = 0,n = random.nextInt(100);i<n;i++) {
            g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);
        }
    /*  方法一：
     * ServletOutputStream out = response.getOutputStream();
        // 转成JPEG格式
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
        // 对图片进行编码
        encoder.encode(bi);
        out.flush();*/
        ImageIO.write(bi, "jpg", response.getOutputStream());


    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

    /**
     * 获取六位随机字符
     */
    public String getRandomString() {
        StringBuffer buffer = new StringBuffer();
        for(int i = 0; i<6;i++) {
            buffer.append(CHARS[random.nextInt(18)]);
        }
        return buffer.toString();
    }

    /**
     * 获取随机颜色
     */
    public  Color getRandomColor() {
        return new Color(random.nextInt(255),random.nextInt(255),random.nextInt(255));
    }

    /**
     * 获取某颜色的反色
     */
    public  Color getReverseColor(Color c) {
        return new Color(255-c.getRed(),255-c.getGreen(),255-c.getBlue());
    }

}

显示界面（作为首页使用）

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>图片验证</title>
<script type="text/javascript">
    function reloadImage(){

        document.getElementById('btn').disabled = true;
        //实时更新,保证每次都从服务器重新请求数据
        document.getElementById('identity').src = '/ServletStudy/IdentityServlet?ts='+new Date().getTime();

    }
</script>
</head>
<body>
<img alt="验证码" src="/ServletStudy/IdentityServlet" id="identity" onload="btn.disabled = false;" />
<input type="button" id="btn" value="换个图片" onclick="reloadImage()">
<form action="/ServletStudy/CheckIdentity" method="post">
  验证码：&nbsp;<input type="text" name="check">
  <input type="submit" value="提交"> 
</form>
</body>
</html>

校验验证码的 Servlet

package cn.joker.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class CheckIdentity
 */
@WebServlet(description = "校验验证码", urlPatterns = { "/CheckIdentity" })
public class CheckIdentity extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public CheckIdentity() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        //request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");
        // 获取客户端上传的数据
        String ch = request.getParameter("check");
        // 获取session 中保存的数据
        String id = (String) request.getSession().getAttribute("randomString");
        if(ch.equals(id))
            response.getWriter().append("<!DOCTYPE html>\r\n" + 
                    "<html>\r\n" + 
                    "<head>\r\n" + 
                    "<meta charset=\"UTF-8\"></head>\r\n" + 
                    "<body>").append("验证码通过").append("</body>\r\n" + 
                            "</html>");
        else
            response.getWriter().append("<!DOCTYPE html>\r\n" + 
                    "<html>\r\n" + 
                    "<head>\r\n" + 
                    "<meta charset=\"UTF-8\"></head>\r\n" + 
                    "<body>").append("验证码错误").append("</body>\r\n" + 
                            "</html>");

    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}