在本文中，您将学习如何使用 Spring Boot 实现 Web 服务中的文件上传和下载功能。首先会构建一个 REST APIs 实现上传及下载的功能，然后使用 Postman 工具来测试这些接口，最后创建一个 Web 界面使用 JavaScript 调用接口演示完整的功能。最终界面及功能如下：
项目环境
- Spring Boot : 2.1.3.RELEASE - Gredle : 5.2.1 - Java : 1.8 - Intellij IDEA : 2018.3.3
项目创建
开发环境为 Intellij IDEA，项目创建很简单，按照下面的步骤创建即可：
- File -> New -> Project...
- 选择 Spring Initializr，点击 Next
- 填写 Group (项目域名) 和 Artifact (项目别名)
- 构建类型可以选择 Maven 或 Gradle， 看个人习惯
- 添加 Web 依赖
- 输入项目名称及保存路径，完成创建
项目创建完毕之后就可以进行开发，项目的完整结构如下图所示：
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.java`POJO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);
@Autowired
private 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 Resource
Resource resource = fileService.loadFileAsResource(fileName);
// Try to determine file's content type
String 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 determined
if(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。
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
@Autowired
public 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 name
String fileName = StringUtils.cleanPath(file.getOriginalFilename());
try {
// Check if the file's name contains invalid characters
if(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);
}
}
}
接口测试
在完成上述的代码之后，打开`SpringBootFileApplication.java`并运行，运行完成之后就可以使用 Postman 进行测试了。
单个文件上传结果：
多个文件上传结果：
文件下载结果：
Web 前端开发
<!DOCTYPE html>
<html lang="zh-cn">
<head>
<!-- Required meta tags -->
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<title>Spring Boot File Upload / Download Rest API Example</title>
<!-- Bootstrap CSS -->
<link href="/css/main.css" rel="stylesheet"/>
</head>
<body>
<noscript>
<h2>Sorry! Your browser doesn't support Javascript</h2>
</noscript>
<div class="upload-container">
<div class="upload-header">
<h2>Spring Boot File Upload / Download Rest API Example</h2>
</div>
<div class="upload-content">
<div class="single-upload">
<h3>Upload Single File</h3>
<form id="singleUploadForm" name="singleUploadForm">
<input id="singleFileUploadInput" type="file" name="file" class="file-input" required/>
<button type="submit" class="primary submit-btn">Submit</button>
</form>
<div class="upload-response">
<div id="singleFileUploadError"></div>
<div id="singleFileUploadSuccess"></div>
</div>
</div>
<div class="multiple-upload">
<h3>Upload Multiple Files</h3>
<form id="multipleUploadForm" name="multipleUploadForm">
<input id="multipleFileUploadInput" type="file" name="files" class="file-input" multiple required/>
<button type="submit" class="primary submit-btn">Submit</button>
</form>
<div class="upload-response">
<div id="multipleFileUploadError"></div>
<div id="multipleFileUploadSuccess"></div>
</div>
</div>
</div>
</div>
<!-- Optional JavaScript -->
<script src="/js/main.js"></script>
</body>
</html>
* {
-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
box-sizing: border-box;
}
body {
margin: 0;
padding: 0;
font-weight: 400;
font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
font-size: 1rem;
line-height: 1.58;
color: #333;
background-color: #f4f4f4;
}
body:before {
height: 50%;
width: 100%;
position: absolute;
top: 0;
left: 0;
background: #128ff2;
content: "";
z-index: 0;
}
.clearfix:after {
display: block;
content: "";
clear: both;
}
h1, h2, h3, h4, h5, h6 {
margin-top: 20px;
margin-bottom: 20px;
}
h1 {
font-size: 1.7em;
}
a {
color: #128ff2;
}
button {
box-shadow: none;
border: 1px solid transparent;
font-size: 14px;
outline: none;
line-height: 100%;
white-space: nowrap;
vertical-align: middle;
padding: 0.6rem 1rem;
border-radius: 2px;
transition: all 0.2s ease-in-out;
cursor: pointer;
min-height: 38px;
}
button.primary {
background-color: #128ff2;
box-shadow: 0 2px 2px 0 rgba(0, 0, 0, 0.12);
color: #fff;
}
input {
font-size: 1rem;
}
input[type="file"] {
border: 1px solid #128ff2;
padding: 6px;
max-width: 100%;
}
.file-input {
width: 100%;
}
.submit-btn {
display: block;
margin-top: 15px;
min-width: 100px;
}
@media screen and (min-width: 500px) {
.file-input {
width: calc(100% - 115px);
}
.submit-btn {
display: inline-block;
margin-top: 0;
margin-left: 10px;
}
}
.upload-container {
max-width: 700px;
margin-left: auto;
margin-right: auto;
background-color: #fff;
box-shadow: 0 1px 11px rgba(0, 0, 0, 0.27);
margin-top: 60px;
min-height: 400px;
position: relative;
padding: 20px;
}
.upload-header {
border-bottom: 1px solid #ececec;
}
.upload-header h2 {
font-weight: 500;
}
.single-upload {
padding-bottom: 20px;
margin-bottom: 20px;
border-bottom: 1px solid #e8e8e8;
}
.upload-response {
overflow-x: hidden;
word-break: break-all;
}
'use strict';
var singleUploadForm = document.querySelector('#singleUploadForm');
var singleFileUploadInput = document.querySelector('#singleFileUploadInput');
var singleFileUploadError = document.querySelector('#singleFileUploadError');
var singleFileUploadSuccess = document.querySelector('#singleFileUploadSuccess');
var multipleUploadForm = document.querySelector('#multipleUploadForm');
var multipleFileUploadInput = document.querySelector('#multipleFileUploadInput');
var multipleFileUploadError = document.querySelector('#multipleFileUploadError');
var multipleFileUploadSuccess = document.querySelector('#multipleFileUploadSuccess');
function uploadSingleFile(file) {
var formData = new FormData();
formData.append("file", file);
var xhr = new XMLHttpRequest();
xhr.open("POST", "/uploadFile");
xhr.onload = function() {
console.log(xhr.responseText);
var response = JSON.parse(xhr.responseText);
if(xhr.status == 200) {
singleFileUploadError.style.display = "none";
singleFileUploadSuccess.innerHTML = "<p>File Uploaded Successfully.</p><p>DownloadUrl : <a href='" + response.fileDownloadUri + "' target='_blank'>" + response.fileDownloadUri + "</a></p>";
singleFileUploadSuccess.style.display = "block";
} else {
singleFileUploadSuccess.style.display = "none";
singleFileUploadError.innerHTML = (response && response.message) || "Some Error Occurred";
}
}
xhr.send(formData);
}
function uploadMultipleFiles(files) {
var formData = new FormData();
for(var index = 0; index < files.length; index++) {
formData.append("files", files[index]);
}
var xhr = new XMLHttpRequest();
xhr.open("POST", "/uploadMultipleFiles");
xhr.onload = function() {
console.log(xhr.responseText);
var response = JSON.parse(xhr.responseText);
if(xhr.status == 200) {
multipleFileUploadError.style.display = "none";
var content = "<p>All Files Uploaded Successfully</p>";
for(var i = 0; i < response.length; i++) {
content += "<p>DownloadUrl : <a href='" + response[i].fileDownloadUri + "' target='_blank'>" + response[i].fileDownloadUri + "</a></p>";
}
multipleFileUploadSuccess.innerHTML = content;
multipleFileUploadSuccess.style.display = "block";
} else {
multipleFileUploadSuccess.style.display = "none";
multipleFileUploadError.innerHTML = (response && response.message) || "Some Error Occurred";
}
}
xhr.send(formData);
}
singleUploadForm.addEventListener('submit', function(event){
var files = singleFileUploadInput.files;
if(files.length === 0) {
singleFileUploadError.innerHTML = "Please select a file";
singleFileUploadError.style.display = "block";
}
uploadSingleFile(files[0]);
event.preventDefault();
}, true);
multipleUploadForm.addEventListener('submit', function(event){
var files = multipleFileUploadInput.files;
if(files.length === 0) {
multipleFileUploadError.innerHTML = "Please select at least one file";
multipleFileUploadError.style.display = "block";
}
uploadMultipleFiles(files);
event.preventDefault();
}, true);