Spring Boot教程之二十一：文件处理

Spring Boot -- 文件处理

Spring Boot 是一种流行的、基于 Spring 的开源框架，用于开发强大的 Web 应用程序和微服务。由于它建立在 Spring 框架之上，因此它不仅具有 Spring 的所有功能，而且还包括某些特殊功能，例如自动配置、健康检查等。这使开发人员能够更轻松地以最少的配置设置基于 Spring 的应用程序，从而促进快速应用程序开发。

Spring Boot 文件处理 是指使用 RESTful Web 服务下载和上传文件。本文将逐步介绍如何使用 Spring Boot 实现可用于上传和下载文件的 RESTful Web 服务。

Spring Boot 中文件处理的初始设置

需要使用 Spring Initializer 创建具有Spring Web依赖项的 Spring Boot 项目，

复制代码

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
 </dependency>

现在让我们开始开发 Spring Boot App。它将为以下对象提供 RESTful Web 服务：

上传文件
下载文件
获取已上传文件名列表

应用程序的实施

步骤 1 ：设置 Application.Properties 文件，其中包含分部分文件上传所需的配置。

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spring.servlet.multipart.enabled=true
spring.servlet.multipart.max-file-size=10MB
spring.servlet.multipart.max-request-size=10MB

这些配置可以解释如下：

spring.servlet.multipart.enabled -> 确定是否必须启用 multipart
spring.servlet.multipart.max-file -> 指定允许上传的文件的最大大小。
spring.servlet.multipart.max-request-size -> 指定允许的 multipart/form-data 请求的最大大小。

步骤 2：创建一个 RestController FileController ，处理以下 REST API：

1. 上传API

用法：可用于上传文件。它使用多部分请求。URL
：/upload
HttpMethod：POST

实施细节：

为了开发此 API，我们使用 MultipartFile 作为请求参数。上传的文件以表单数据的形式发送，然后在 Rest 控制器中作为 Multipart 文件检索。因此，MultipartFile只不过是在多部分请求中收到的上传文件的一种表示。

2. 获取文件 API

用法：可用于获取已上传的文件名列表。URL
：/getFIles
HttpMethod：GET

实施细节：

它可以简单地通过使用java.io.File 的**list()**方法来实现，该方法返回一个字符串数组，该数组命名由给定的抽象路径名表示的目录中的文件和目录。

3. 下载API

它可用于下载先前上传的文件。URL
：/download/{filename}
HttpMethod：POST

实施细节：

要实现此 API，我们首先检查所请求下载的文件是否存在于上传的文件夹中。如果文件存在，我们使用InputStreamResource 下载该文件。还需要将响应标头中的 Content-Disposition 设置为附件**，** 并将MediaType 设置为application/octet-stream。

Content -Disposition 响应头作为附件， 表示要下载内容。contentType设置为 application/octet-stream **，**这样当尝试下载缺少扩展名或格式未知的文件时，系统会将其识别为八位字节流文件。FileController 的实现如下所示：

Java

|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| // Java Program to Create Rest Controller // that Defines various API for file handling package com.SpringBootFileHandling.controller; // Importing required classes import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.util.Arrays; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.core.io.InputStreamResource; import org.springframework.http.HttpHeaders; import org.springframework.http.HttpStatus; import org.springframework.http.MediaType; import org.springframework.http.ResponseEntity; import org.springframework.web.bind.annotation.PathVariable; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RequestMethod; import org.springframework.web.bind.annotation.RequestParam; import org.springframework.web.bind.annotation.RestController; import org.springframework.web.multipart.MultipartFile; // Annotation @RestController public class FileController { // Uploading a file @RequestMapping(value = "/upload", method = RequestMethod.POST) public String uploadFile(@RequestParam("file") MultipartFile file){ // Setting up the path of the file String filePath = System.getProperty("user.dir") + "/Uploads" + File.separator + file.getOriginalFilename(); String fileUploadStatus; // Try block to check exceptions try { // Creating an object of FileOutputStream class FileOutputStream fout = new FileOutputStream(filePath); fout.write(file.getBytes()); // Closing the connection fout.close(); fileUploadStatus = "File Uploaded Successfully"; } // Catch block to handle exceptions catch (Exception e) { e.printStackTrace(); fileUploadStatus = "Error in uploading file: " + e; } return fileUploadStatus; } // Getting list of filenames that have been uploaded @RequestMapping(value = "/getFiles", method = RequestMethod.GET) public String[] getFiles() { String folderPath = System.getProperty("user.dir") +"/Uploads"; // Creating a new File instance File directory= new File(folderPath); // list() method returns an array of strings // naming the files and directories // in the directory denoted by this abstract pathname String[] filenames = directory.list(); // returning the list of filenames return filenames; } // Downloading a file @RequestMapping(value = "/download/{path:.+}", method = RequestMethod.GET) public ResponseEntity downloadFile(@PathVariable("path") String filename) throws FileNotFoundException { // Checking whether the file requested for download exists or not String fileUploadpath = System.getProperty("user.dir") +"/Uploads"; String[] filenames = this.getFiles(); boolean contains = Arrays.asList(filenames).contains(filename); if(!contains) { return new ResponseEntity("FIle Not Found",HttpStatus.NOT_FOUND); } // Setting up the filepath String filePath = fileUploadpath+File.separator+filename; // Creating new file instance File file= new File(filePath); // Creating a new InputStreamResource object InputStreamResource resource = new InputStreamResource(new FileInputStream(file)); // Creating a new instance of HttpHeaders Object HttpHeaders headers = new HttpHeaders(); // Setting up values for contentType and headerValue String contentType = "application/octet-stream"; String headerValue = "attachment; filename=\"" + resource.getFilename() + "\""; return ResponseEntity.ok() .contentType(MediaType.parseMediaType(contentType)) .header(HttpHeaders.CONTENT_DISPOSITION, headerValue) .body(resource); } } |