Spring Boot 檔案上傳與下載

JamesGeek發表於2019-03-29
Spring Boot

檔案的上傳及下載功能是開發人員在日常應用及程式設計開發中經常會遇到的。正好最近開發需要用到此功能，雖然本人是 Android 開發人員，但還是業餘客串了一下後臺開發。

在本文中，您將學習如何使用 Spring Boot 實現 Web 服務中的檔案上傳和下載功能。首先會構建一個 REST APIs 實現上傳及下載的功能，然後使用 Postman 工具來測試這些介面，最後建立一個 Web 介面使用 JavaScript 呼叫介面演示完整的功能。最終介面及功能如下：

show_demo.png

專案環境

- Spring Boot : 2.1.3.RELEASE
- Gredle : 5.2.1
- Java : 1.8
- Intellij IDEA : 2018.3.3
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專案建立

開發環境為 Intellij IDEA，專案建立很簡單，按照下面的步驟建立即可：

  1. File -> New -> Project...
  2. 選擇 Spring Initializr，點選 Next
  3. 填寫 Group (專案域名) 和 Artifact (專案別名)
  4. 構建型別可以選擇 Maven 或 Gradle， 看個人習慣
  5. 新增 Web 依賴
  6. 輸入專案名稱及儲存路徑，完成建立

專案建立完畢之後就可以進行開發，專案的完整結構如下圖所示：

project_structure.png

引數配置

專案建立完成之後，需要設定一些必要的引數，開啟專案resources目錄下配置檔案application.properties，在其中新增以下引數：

server.port=80

## MULTIPART (MultipartProperties)
# 開啟 multipart 上傳功能
spring.servlet.multipart.enabled=true
# 檔案寫入磁碟的閾值
spring.servlet.multipart.file-size-threshold=2KB
# 最大檔案大小
spring.servlet.multipart.max-file-size=200MB
# 最大請求大小
spring.servlet.multipart.max-request-size=215MB

## 檔案儲存所需引數
# 所有通過 REST APIs 上傳的檔案都將儲存在此目錄下
file.upload-dir=./uploads
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其中file.upload-dir=./uploads引數為自定義的引數，建立FileProperties.javaPOJO類，使配置引數可以自動繫結到POJO類。

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;
    }
}
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然後在@SpringBootApplication註解的類中新增@EnableConfigurationProperties註解以開啟ConfigurationProperties功能。

SpringBootFileApplication.java

@SpringBootApplication
@EnableConfigurationProperties({
        FileProperties.class
})
public class SpringBootFileApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringBootFileApplication.class, args);
    }
}
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配置完成，以後若有file字首開頭的引數需要配置，可直接在application.properties配置檔案中配置並更新FileProperties.java即可。

另外再建立一個上傳檔案成功之後的Response響應實體類UploadFileResponse.java及異常類FileException.java來處理異常資訊。

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 ...
}
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FileException.java

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

    public FileException(String message, Throwable cause) {
        super(message, cause);
    }
}
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建立介面

下面需要建立檔案上傳下載所需的 REST APIs 介面。建立檔案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);
    }
}
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FileController類在接收到使用者的請求後，使用FileService類提供的storeFile()方法將檔案寫入到系統中進行儲存，其儲存目錄就是之前在application.properties配置檔案中的file.upload-dir引數的值./uploads。

下載介面downloadFile()在接收到使用者請求之後，使用FileService類提供的loadFileAsResource()方法獲取儲存在系統中檔案並返回檔案供使用者下載。

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; // 檔案在本地儲存的地址

    @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);
        }
    }

    /**
     * 儲存檔案到系統
     *
     * @param file 檔案
     * @return 檔名
     */
    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);
        }
    }

    /**
     * 載入檔案
     * @param fileName 檔名
     * @return 檔案
     */
    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);
        }
    }
}
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介面測試

在完成上述的程式碼之後，開啟SpringBootFileApplication.java並執行，執行完成之後就可以使用 Postman 進行測試了。

單個檔案上傳結果：

upload_result1.png

多個檔案上傳結果：

upload_result2.png

檔案下載結果：

download_result.png

Web 前端開發

index.html

<!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>
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main.css

* {
    -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;
}
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main.js

'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);
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總結

至此，檔案的上傳及下載功能已完成。在正式環境中可能還需要將上傳的檔案儲存到資料庫，此處按照實際需求去處理即可。

本文原始碼地址：github.com/JemGeek/spr…

本文參考(需要FQ)：www.callicoder.com/spring-boot…

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