Spring Boot实现文件上传与下载，包括前端界面实现

效果展示：

新建SpringBoot工程

（略...）

参数配置

项目创建完成之后，需要设置一些必要的参数，打开项目resources目录下配置文件application.properties，在其中添加以下参数：

server.port=80## MULTIPART (MultipartProperties)
# 开启 multipart 上传功能
spring.servlet.multipart.enabled=true
# 文件写入磁盘的阈值
spring.servlet.multipart.file-size-threshold=2KB
# 最大文件大小
spring.servlet.multipart.max-file-size=200MB
# 最大请求大小
spring.servlet.multipart.max-request-size=215MB## 文件存储所需参数
# 所有通过 REST APIs 上传的文件都将存储在此目录下
file.upload-dir=./uploads

其中file.upload-dir=./uploads参数为自定义的参数，创建FileProperties.javaPOJO类，使配置参数可以自动绑定到POJO类。

import org.springframework.boot.context.properties.ConfigurationProperties;@ConfigurationProperties(prefix = "file")
public class FileProperties {private String uploadDir;public String getUploadDir() {return uploadDir;}public void setUploadDir(String uploadDir) {this.uploadDir = uploadDir;}
}

然后在@SpringBootApplication注解的类中添加@EnableConfigurationProperties注解以开启ConfigurationProperties功能。

SpringBootFileApplication.java

@SpringBootApplication
@EnableConfigurationProperties({FileProperties.class
})
public class SpringBootFileApplication {public static void main(String[] args) {SpringApplication.run(SpringBootFileApplication.class, args);}
}

配置完成，以后若有file前缀开头的参数需要配置，可直接在application.properties配置文件中配置并更新FileProperties.java即可。

另外再创建一个上传文件成功之后的Response响应实体类UploadFileResponse.java及异常类FileException.java来处理异常信息。

UploadFileResponse.java

public class UploadFileResponse {private String fileName;private String fileDownloadUri;private String fileType;private long size;public UploadFileResponse(String fileName, String fileDownloadUri, String fileType, long size) {this.fileName = fileName;this.fileDownloadUri = fileDownloadUri;this.fileType = fileType;this.size = size;}// getter and setter ...
}

FileException.java

public class FileException extends RuntimeException{public FileException(String message) {super(message);}public FileException(String message, Throwable cause) {super(message, cause);}
}

创建接口

下面需要创建文件上传下载所需的 REST APIs 接口。创建文件FileController.java。

import com.james.sample.file.dto.UploadFileResponse;
import com.james.sample.file.service.FileService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.io.Resource;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.servlet.support.ServletUriComponentsBuilder;import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;@RestController
public class FileController {private static final Logger logger = LoggerFactory.getLogger(FileController.class);@Autowiredprivate FileService fileService;@PostMapping("/uploadFile")public UploadFileResponse uploadFile(@RequestParam("file") MultipartFile file){String fileName = fileService.storeFile(file);String fileDownloadUri = ServletUriComponentsBuilder.fromCurrentContextPath().path("/downloadFile/").path(fileName).toUriString();return new UploadFileResponse(fileName, fileDownloadUri,file.getContentType(), file.getSize());}@PostMapping("/uploadMultipleFiles")public List<UploadFileResponse> uploadMultipleFiles(@RequestParam("files") MultipartFile[] files) {return Arrays.stream(files).map(this::uploadFile).collect(Collectors.toList());}@GetMapping("/downloadFile/{fileName:.+}")public ResponseEntity<Resource> downloadFile(@PathVariable String fileName, HttpServletRequest request) {// Load file as ResourceResource resource = fileService.loadFileAsResource(fileName);// Try to determine file's content typeString contentType = null;try {contentType = request.getServletContext().getMimeType(resource.getFile().getAbsolutePath());} catch (IOException ex) {logger.info("Could not determine file type.");}// Fallback to the default content type if type could not be determinedif(contentType == null) {contentType = "application/octet-stream";}return ResponseEntity.ok().contentType(MediaType.parseMediaType(contentType)).header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + resource.getFilename() + "\"").body(resource);}
}

FileController类在接收到用户的请求后，使用FileService类提供的storeFile()方法将文件写入到系统中进行存储，其存储目录就是之前在application.properties配置文件中的file.upload-dir参数的值./uploads。

下载接口downloadFile()在接收到用户请求之后，使用FileService类提供的loadFileAsResource()方法获取存储在系统中文件并返回文件供用户下载。

FileService.java

import com.james.sample.file.exception.FileException;
import com.james.sample.file.property.FileProperties;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.io.Resource;
import org.springframework.core.io.UrlResource;
import org.springframework.stereotype.Service;
import org.springframework.util.StringUtils;
import org.springframework.web.multipart.MultipartFile;import java.io.IOException;
import java.net.MalformedURLException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardCopyOption;@Service
public class FileService {private final Path fileStorageLocation; // 文件在本地存储的地址@Autowiredpublic FileService(FileProperties fileProperties) {this.fileStorageLocation = Paths.get(fileProperties.getUploadDir()).toAbsolutePath().normalize();try {Files.createDirectories(this.fileStorageLocation);} catch (Exception ex) {throw new FileException("Could not create the directory where the uploaded files will be stored.", ex);}}/*** 存储文件到系统** @param file 文件* @return 文件名*/public String storeFile(MultipartFile file) {// Normalize file nameString fileName = StringUtils.cleanPath(file.getOriginalFilename());try {// Check if the file's name contains invalid charactersif(fileName.contains("..")) {throw new FileException("Sorry! Filename contains invalid path sequence " + fileName);}// Copy file to the target location (Replacing existing file with the same name)Path targetLocation = this.fileStorageLocation.resolve(fileName);Files.copy(file.getInputStream(), targetLocation, StandardCopyOption.REPLACE_EXISTING);return fileName;} catch (IOException ex) {throw new FileException("Could not store file " + fileName + ". Please try again!", ex);}}/*** 加载文件* @param fileName 文件名* @return 文件*/public Resource loadFileAsResource(String fileName) {try {Path filePath = this.fileStorageLocation.resolve(fileName).normalize();Resource resource = new UrlResource(filePath.toUri());if(resource.exists()) {return resource;} else {throw new FileException("File not found " + fileName);}} catch (MalformedURLException ex) {throw new FileException("File not found " + fileName, ex);}}
}

代码下载