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Servlet simple verification code generation

2022-07-04 01:48:00 【Travel · lost road】

The essence ： A picture

Purpose ： Prevent malicious form registration

Servlet backstage ：

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

@WebServlet("/checkCodeServlet")
public class CheckCodeServlet extends HttpServlet implements Servlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // Set the height and width of the verification code image 
        int width = 100;
        int height = 50;

        //1. Create an object , Picture in memory （ Captcha image object ）
        BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);

        //2. Beautify the picture 

        //2.1 Fill background color 
        Graphics g = image.getGraphics();// Brush object 
        g.setColor(Color.white);
        g.fillRect(0,0,width,height);

        //2.2 Picture frame 
        g.setColor(Color.black);
        g.drawRect(0,0,width-1,height-1);

        String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        // Generate random corners 
        Random r = new Random();

        for (int i = 1; i <= 4; i++) {
            int index = r.nextInt(str.length());
            // Character acquisition 
            char ch = str.charAt(index);
        //2.3 Write verification code 
            g.drawString(ch+"",width/5*i,height/2);
        }

        //2.4 Drew interference 
        g.setColor(Color.green);
        // Randomly generate coordinate points 
        for (int i = 0; i < 6; i++) {
            int x1 = r.nextInt(width);
            int x2 = r.nextInt(width);
            int y1 = r.nextInt(height);
            int y2 = r.nextInt(height);
            g.drawLine(x1,y1,x2,y2);
        }

        //3. Output the picture to the page to show 
        ImageIO.write(image,"jpg",response.getOutputStream());
    }

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


}

HTML front end ：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        window.onload = function () {
            var img = document.getElementById("checkCode")
            img.onclick = function () {
                // Time stamp 
                var date = new Date().getTime();
                img.src = "/day15/checkCodeServlet?"+date;
            }
        }
    </script>
</head>
<body>
    <img id="checkCode" src="/day15/checkCodeServlet">
    <a id="change"  href=""> I can't see it clearly. Change it ?</a>
</body>
</html>

The effect is as follows ：