Response_驗證碼_分析以及程式碼實現

本質：圖片

目的：防止惡意表單註冊

步驟：

　　1.建立物件，在記憶體中圖片（驗證碼圖片物件）

　　2.美化圖片

　　3.將圖片輸出到頁面展示

package com.example.servlet;

import javax.imageio.ImageIO;
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(name = "ResponseDemo5", value = "/ResponseDemo5")
public class ResponseDemo5 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws
 
 ServletException, IOException {
        this.doPost(request, response);
    }

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

        int width = 100;// 高
        int height = 50;// 寬

        //1.建立一物件，在記憶體中圖片
        BufferedImage image = new
 
 BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);

        //2.美化圖片
        //2.1填充背景色
        Graphics g = image.getGraphics();//畫筆物件
        g.setColor(Color.PINK);//設定畫筆顏色
        g.fillRect(0, 0, width, height);

        //2.2畫邊框
        g.setColor(Color.BLACK);
        g.drawRect(0, 0, width - 1, height - 1);

        String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghigklmnopqrstuvwxyz0123456789";
        //生成隨機角標
        Random ran = new Random();

        for (int i = 1; i <= 4; i++) {
            int index = ran.nextInt(str.length());
            //獲取字元
            char ch = str.charAt(index);//隨機字元
            //2.3驗證碼
            g.drawString(ch+"", width/5*i, height/2);
        }

        //2.4畫干擾線
        g.setColor(Color.GREEN);
        //隨機生成座標點
        for (int i = 0; i < 10; i++) {
            int x1 = ran.nextInt(width);
            int x2 = ran.nextInt(width);

            int y1 = ran.nextInt(height);
            int y2 = ran.nextInt(height);
            g.drawLine(x1, x2, y1, y2);
        }
        
        //3.將圖片輸出到頁面展示
        ImageIO.write(image, "jpg", response.getOutputStream());
    }
}