验证码简单例子

原创于 2020-07-12 20:07:06 发布 · 6.9k 阅读

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#验证码 #表单

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本文详细介绍了如何使用Java Servlet生成带有验证码的图片，并通过在URL中添加时间戳来实现验证码的刷新功能，确保每次请求都能获取到新的验证码图片。

本质：图片
目的：防止恶意表单注册

先输出一张简单的图片

资源ServletDemo5代码

package com.lingaolu.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.awt.image.BufferedImage;
import java.io.IOException;

/**
 * @author 林高禄
 * @create 2020-07-12-17:52
 */
@WebServlet("/servletDemo5")
public class ServletDemo5 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int width = 100;
        int height = 50;
        // 创建内存中的图片
        BufferedImage image = new BufferedImage(width,height, BufferedImage.TYPE_INT_RGB);

        // 将图片输出到页面展示
        ImageIO.write(image,"jpg",response.getOutputStream());
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

}

浏览器访问

往图片加验证码

package com.lingaolu.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

/**
 * @author 林高禄
 * @create 2020-07-12-17:52
 */
@WebServlet("/servletDemo5")
public class ServletDemo5 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int width = 100;
        int height = 50;
        // 创建内存中的图片
        BufferedImage image = new BufferedImage(width,height, BufferedImage.TYPE_INT_RGB);
        // 美化图片，填写验证码
        Graphics g = image.getGraphics();
        // 填充黄色
        g.setColor(Color.YELLOW);
        g.fillRect(0,0,width,height);
        // 边框蓝色
        g.setColor(Color.blue);
        g.drawRect(0,0,width-2,height-2);
        // 填写验证码
        String str = "あいうえおかきくけこさしすせそたちつてとなにぬんへのはひふへほまみむめもやゆよらりるれろわを";
        int length = str.length();
        Random ran = new Random();
        for(int i=1;i<=4;i++){
            g.drawString(str.charAt(ran.nextInt(length))+"",i*width/5,height/2);
        }
        // 画干扰线
        g.setColor(Color.GREEN);
        for(int i=0;i<10;i++){
            g.drawLine(ran.nextInt(width),ran.nextInt(height),ran.nextInt(width),ran.nextInt(height));
        }
        // 将图片输出到页面展示
        ImageIO.write(image,"jpg",response.getOutputStream());
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

}

浏览器访问

加一个页面d.html，可以刷新验证码

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>验证码</title>
</head>
<body>
   <img id="imgId" src="/bServlet/servletDemo5" onclick="code(this)">
   <a onclick="code(document.getElementById('imgId'))" href="javascript:void(0)">看不清换一张？</a>
   <script>
       function code(object) {
           // 加时间戳，这样每次连接不一样，图片就不会从缓存拿
           object.src="/bServlet/servletDemo5?"+new Date().getTime();
       }

   </script>
</body>
</html>