Java文件上传下载接口实现

1.文件上传接口

首先是Controller层的入口方法
@ApiOperation注解是swagger接口文档的，没用这个可以直接删掉
@RequestParam注解是用来接收其它参数的，我这个是为了标记文件类型的，比如是临时文件还是其它文件

import org.springframework.web.multipart.MultipartFile;


	@PostMapping("/upload")
    @ApiOperation(value = "上传文件")
    public Map upload(@RequestPart("file") MultipartFile file, @RequestParam(value = "mediaLibrary") Integer mediaLibrary) throws Exception {
        Map map = fileService.upload(file, mediaLibrary);
        return map;
    }

这个接口在postman上传参是下面这样的：
注意里面的参数名称要和接口上的一致，不然会拿不到值
还有file那里key的类型要选file类型的，这样就可以在后面value里面选择文件

然后是Service方法
这里面LOCAL_HOST就是取配置文件里面的项目访问路径比如http://127.0.0.1:8080/，或者你的域名
上传的文件都保存在根目录./resources/files/下了，也就是跟部署的jar包同目录下
UploadFile 是用来记录上传文件的实体类，方便做文件列表管理的

import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.sakura.base.exception.BizException;
import com.sakura.base.utils.DateUtil;
import com.sakura.base.utils.FileTypeTool;
import com.sakura.entity.UploadFile;
import com.sakura.demo.mapper.UploadFileMapper;
import com.sakura.demo.service.FileService;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.io.IOUtils;
import org.apache.commons.lang3.RandomStringUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.web.multipart.MultipartFile;

import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.util.HashMap;
import java.util.Map;



	@Override
	@Transactional
    public Map upload(MultipartFile multipartFile, Integer mediaLibrary) throws Exception {
        if (multipartFile.isEmpty()) {
            throw new BizException(500, "上传文件为空");
        }
        UploadFile uploadFile = new UploadFile();
        // 保存原文件名称，文件列表展示需要用到
        uploadFile.setFileName(multipartFile.getOriginalFilename());
        // 生成系统文件名称，不可重复，防止同名文件上传覆盖问题
        String name = RandomStringUtils.randomAlphanumeric(32) + multipartFile.getOriginalFilename().substring(multipartFile.getOriginalFilename().lastIndexOf(".")).toLowerCase();
        uploadFile.setName(name.substring(0, name.lastIndexOf(".")));
        uploadFile.setFileSuffix(multipartFile.getOriginalFilename().substring(multipartFile.getOriginalFilename().lastIndexOf(".")).toLowerCase());
        // 判断文件类型
        int fileType = FileTypeTool.fileType(name);
        uploadFile.setType(fileType);
        uploadFile.setDomain(LOCAL_HOST + "file/");
        uploadFile.setPath(LOCAL_HOST + "file/" + name.substring(0, name.lastIndexOf(".")));
        uploadFile.setPathExt(DateUtil.today());
        // 获取文件大小
        uploadFile.setSize((int)multipartFile.getSize());
        uploadFile.setMediaLibrary(mediaLibrary);
        uploadFile.setStatus(1);
        uploadFileMapper.insert(uploadFile);

        // 将文件保存到本目录/resources/files/下
        // DateUtil.today()得到得是当天日期如：20230715，这个会在/resources/files/下再以日期生成一层目录
        File newFile = new File("./resources/files/" + DateUtil.today() + "/" + name);
        // 保证这个文件的父文件夹必须要存在
        if (!newFile.getParentFile().exists()) {
            newFile.getParentFile().mkdirs();
        }
        newFile.createNewFile();
        // 将文件内容写入到这个文件中
        InputStream is = multipartFile.getInputStream();
        FileOutputStream fos = new FileOutputStream(newFile);
		try {
            int len;
            byte[] buf = new byte[1024];
            while ((len = is.read(buf)) != -1) {
                fos.write(buf, 0, len);
            }
        } finally {
            // 关流顺序，先打开的后关闭
            fos.close();
            is.close();
        }

        // 返回文件信息给前端
        Map resultMap = new HashMap();
        resultMap.put("id", uploadFile.getId());
        resultMap.put("path", uploadFile.getPath());
        resultMap.put("code", 200);
        resultMap.put("message", "请求成功！");
        return resultMap;
    }

2.文件下载接口

刚才上传路径返回给前端的路径是这样的：http://127.0.0.1:8080/file/ojod5g3as12g3sd2g13g1a3g1g785ef9
所以要拿到这个文件还需要下面这个下载的接口
同样的Controller的入口方法

	@GetMapping("/{name}")
    @ApiOperation(value = "下载", response = ApiResult.class)
    public void download(HttpServletResponse response, @PathVariable("name") String name) throws Exception {
        fileService.download(response, name);
    }

然后是Service方法

import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.sakura.base.exception.BizException;
import com.sakura.base.utils.DateUtil;
import com.sakura.base.utils.FileTypeTool;
import com.sakura.entity.UploadFile;
import com.sakura.demo.mapper.UploadFileMapper;
import com.sakura.demo.service.FileService;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.io.IOUtils;
import org.apache.commons.lang3.RandomStringUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.web.multipart.MultipartFile;

import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.util.HashMap;
import java.util.Map;



	@Override
    public void download(HttpServletResponse response, String name) throws Exception {
        LambdaQueryWrapper<UploadFile> wrapper = new LambdaQueryWrapper<>();
        wrapper.eq(UploadFile::getName, name);
        wrapper.eq(UploadFile::getStatus, 1);
        UploadFile uploadFile = uploadFileMapper.selectOne(wrapper);
        if (uploadFile == null) {
            throw new BizException(500, "文件不存在");
        }

		// 去./resources/files/目录下取出文件
        File downloadFile = File("./resources/files/" + uploadFile.getPathExt() + "/" + name + uploadFile.getFileSuffix());
        if(!downloadFile.exists() || downloadFile.length() == 0) {
            throw new BizException(500, "文件不存在");
        }

        InputStream is = null;
        OutputStream os = null;
        try {
        	// 判断是否是图片，如果是图片加上 response.setContentType("image/jpeg")，这样就可以直接在浏览器打开而不是下载
            if (uploadFile.getType() == 1) {
                response.setContentType("image/jpeg");
            }
            response.addHeader("Content-Length", "" + downloadFile.length());
            is = new FileInputStream(downloadFile);
            os = response.getOutputStream();
            IOUtils.copy(is, os);
        } catch (Exception e) {
            log.error("下载图片发生异常", e);
        } finally {
            try {
                if (os != null) {
                    os.flush();
                    os.close();
                }
                if (is != null) {
                    is.close();
                }
            } catch (IOException e) {
                log.error("关闭流发生异常", e);
            }
        }
    }

3.其它工具类，根据文件后缀判断文件类型的

package com.sakura.base.utils;

public class FileTypeTool {

	public static int fileType(String fileName) {
		if (fileName == null) {
			return 0;
		} else {
			// 获取文件后缀名并转化为写，用于后续比较
			String fileType = fileName.substring(fileName.lastIndexOf(".") + 1).toLowerCase();
			// 创建图片类型数组
			String img[] = {"bmp", "jpg", "jpeg", "png", "tiff", "gif", "pcx", "tga", "exif", "fpx", "svg", "psd",
					"cdr", "pcd", "dxf", "ufo", "eps", "ai", "raw", "wmf"};
			for (int i = 0; i < img.length; i++) {
				if (img[i].equals(fileType)) {
					return 1;
				}
			}
			// 创建文档类型数组
			String document[] = {"txt", "doc", "docx", "xls", "htm", "html", "jsp", "rtf", "wpd", "pdf", "ppt"};
			for (int i = 0; i < document.length; i++) {
				if (document[i].equals(fileType)) {
					return 2;
				}
			}
			// 创建视频类型数组
			String video[] = {"mp4", "avi", "mov", "wmv", "asf", "navi", "3 gp", "mkv", "f4v", "rmvb", "webm"};
			for (int i = 0; i < video.length; i++) {
				if (video[i].equals(fileType)) {
					return 3;
				}
			}
			// 创建音乐类型数组
			String music[] = {"mp3", "wma", "wav", "mod", "ra", "cd", "md", "asf", "aac", "vqf", "ape", "mid", "ogg",
					"m4a", "vqf"};
			for (int i = 0; i < music.length; i++) {
				if (music[i].equals(fileType)) {
					return 4;
				}
			}
		}
		return 0;
	}
}