HttpServletResponse

1、Response文件下载

package com.kuang;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.URLEncoder;
import java.util.Random;

public class filePath extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 1 获取下载的路径
             String filePath="C:\\path\\javaweb\\response\\src\\main\\resources\\1.png";
        //2 下载的文件名是啥
        String substring = filePath.substring(filePath.lastIndexOf("\\") + 1);
          //3 设置想办法让浏览器能够支持下载我们需要的东西
        resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(filePath,"UTF-8"));
//     4 获取下载文件的输入流
        FileInputStream InputStream = new FileInputStream(filePath);
//      5  创建缓冲区
        int len ;
        byte[] buffer = new byte[1024];
//      6 获取OutputStream对象
        ServletOutputStream outputStream = resp.getOutputStream();
//      7  将FileOutputStream流写入到bufer缓冲区 8 使用OutputStream将缓冲区中的数据输出到客户端！
         while ((len=InputStream.read())!=-1){
             outputStream.write(buffer,0,len);
         }

        InputStream.close();
         outputStream.close();

    
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}
2、随机生成6为数验证码

Random random = new Random();
String s = random.nextInt(111111)+"";
StringBuffer buffer1 = new StringBuffer(); 
for (int i = 0; i < 6-s.length(); i++) {   // 这里必须得判断，不然可能会生成不是6位数
       buffer1.append("0");
}
String s2=s+buffer1.toString();