关于Javaweb设置浏览器缓存（附带还有一个实现验证码生成的操作——基于Random类和ImageIO的骚操作

关于设置浏览器缓存的：
https://blog.csdn.net/iemdm1110/article/details/52183459
https://blog.csdn.net/mustbehard/article/details/20702747

package com.woshi.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("/image")
public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setHeader("refresh", "3");
        BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);

        Graphics2D graphics2D = (Graphics2D) image.getGraphics();
        graphics2D.setColor(Color.white);
        graphics2D.fillRect(0, 0, 80, 20);
        graphics2D.setColor(Color.blue);
        graphics2D.setFont(new Font(null, Font.BOLD, 20));
        graphics2D.drawString(randomNum(), 0, 20);

        resp.setContentType("image/png");
        resp.setDateHeader("exprise", -1);
        resp.setHeader("Cache-control", "no-cache");
        resp.setHeader("Pragma", "no-cache");

        ImageIO.write(image, "png", resp.getOutputStream());
    }

    public String randomNum(){
        Random random = new Random();
        String num = random.nextInt(1111)+"";
        StringBuffer stringBuffer = new StringBuffer();
        for (int i =0;i<4-num.length();i++){
            stringBuffer.append("0");
        }
        String result = stringBuffer.toString()+num;
        return result;
    }
}