servlet 实现简易验证码

一.验证码本质解释

1.本质：图片
2.目的：防止恶意表单注册

二.验证码生成过程分析

新建JavaWeb 项目，在src 下新建Servlet ，编写servlet逻辑代码

三.代码实现

新建JavaWeb 项目，在src 下新建Servlet ，编写servlet逻辑代码，在tomcat服务器部署项目

servlet 代码如下

import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

import javax.imageio.ImageIO;
import javax.imageio.plugins.jpeg.JPEGImageWriteParam;
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 {

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        int width=500;
        int height=300;
        BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);


        //美化图片
        //2.1 填充背景色
        Graphics g = image.getGraphics();
        g.setColor(Color.pink);
        g.fillRect(0,0,width,height);

        //画边框
        g.setColor(Color.red);
        g.drawRect(0,0,width-1,height-1);
        String str = "QWERTYUIOPASDFGHJKLZXCVBNMqwertyuiopasdfghjklzxcvbnm1234567890";
        //生成随机角标
        g.setColor(Color.blue);
        Random rand = new Random();
        //写验证码
        for (int i = 0; i <=4; i++) {
            int index= rand.nextInt(str.length());
            char ch= str.charAt(index);
            g.drawString(ch+"",width/5*i,height/2);
        }

        //画干扰线
        g.setColor(Color.GREEN);
        for (int i = 0; i <10 ; i++) {
            int x1=rand.nextInt(width);
            int x2=rand.nextInt(width);

            int y1=rand.nextInt(width);
            int y2=rand.nextInt(width);



            g.drawLine(x1,y1,x2,y2);
        }



        //将图片输出到页面
//        ImageIO.write(image,"jpg",resp.getOutputStream());
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(resp.getOutputStream());


        encoder.encode(image);


    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
      this.doPost(req, resp);
    }
}

四.实现效果

部署完成后，刷新浏览器页面，即可实现验证码图片的更新

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