文件下载实现

代码示例
```bash
package com.ruoyi.web.controller.family;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.ruoyi.common.config.RuoYiConfig;
import com.ruoyi.common.utils.StringUtils;
import com.ruoyi.common.utils.file.FileUtils;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import sun.misc.BASE64Encoder;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.nio.charset.StandardCharsets;

import sun.misc.BASE64Encoder;

@RestController
@RequestMapping("/family/testxiazai")
public class TestxiazaiController {

    /**
     * 下载文件的demo
     */
    @GetMapping("/doGet")
    public void downloadFile(HttpServletRequest request, HttpServletResponse response) {
        File file = new File("E:\\图片\\张敏.jpg");
        String fileName = "张敏.jpg";
        downloadFile(fileName,file,response,request);
    }
    /**
     * 下载文件
     * @param originalFileName ：下载文件的原始文件名
     * @param file             ：下载的文件
     * @param response         ：相应对象
     */
    public static void downloadFile(String originalFileName, File file, HttpServletResponse response, HttpServletRequest request) {
        // 数据校验
        checkParam(originalFileName,file);

        //相应头的处理
        //清空response中的输出流
        response.reset();
        //设置文件大小
        response.setContentLength((int) file.length());
        //设置Content-Type头
        response.setContentType("application/octet-stream;charset=UTF-8");
        //设置Content-Disposition头 以附件形式解析
        String encodedFilename = getEncodedFilename(request, originalFileName);
        response.addHeader("Content-Disposition", "attachment;filename=" + encodedFilename);

        //将来文件流写入response中
        FileInputStream fileInputStream = null;
        ServletOutputStream outputStream = null;
        try {
            //获取文件输入流
            fileInputStream = new FileInputStream(file);
            //创建数据缓冲区
            byte[] buffers = new byte[1024];
            //通过response中获取ServletOutputStream输出流
            outputStream = response.getOutputStream();
            int length;
            while ((length = fileInputStream.read(buffers)) > 0) {
                //写入到输出流中
                outputStream.write(buffers, 0, length);
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //流的关闭
            if(fileInputStream != null){
                try {
                    fileInputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (outputStream != null) {
                try {
                    outputStream.flush();
                    outputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    /**
     * 下载文件的参数的校验，如果参数不合法则抛出自定义异常
     * @param originalFileName ：文件原始文件名
     * @param file ：待下载的文件
     */
    private static void checkParam(String originalFileName, File file) {
        if(StringUtils.isBlank(originalFileName)){

        }
        if(file == null || !file.exists() ){
        }
    }

    /**
     * 获取URL编码后的原始文件名
     * @param request ：客户端请求
     * @param originalFileName ：原始文件名
     * @return ：
     */
    private static String getEncodedFilename(HttpServletRequest request, String originalFileName) {
        String encodedFilename = null;
        String agent = request.getHeader("User-Agent");
        if(agent.contains("MSIE")){
            //IE浏览器
            try {
                encodedFilename = URLEncoder.encode(originalFileName, "utf-8");
                encodedFilename = encodedFilename.replace("+", " ");
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
        }else if(agent.contains("Firefox")){
            //火狐浏览器
            BASE64Encoder base64Encoder = new BASE64Encoder();
            encodedFilename = "=?utf-8?B?" + base64Encoder.encode(originalFileName.getBytes(StandardCharsets.UTF_8))+"?=";
        }else{
            //其他浏览器
            try {
                encodedFilename = URLEncoder.encode(originalFileName, "utf-8");
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
        }
        return encodedFilename;
    }



}

参考文件https://blog.youkuaiyun.com/ycd500756/article/details/87907525?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522161585922616780261983241%2522%252C%2522scm%2522%253A%252220140713.130102334.pc%255Fall.%2522%257D&request_id=161585922616780261983241&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~first_rank_v2~rank_v29-4-87907525.first_rank_v2_pc_rank_v29&utm_term=%E9%99%84%E4%BB%B6%E4%B8%8B%E8%BD%BD%E5%89%8D%E5%90%8E%E7%AB%AF%E4%BB%A3%E7%A0%81