Build Restful File Upload & Download APIs with Spring Boot 2.2.6

File upload and download are common features in web applications. This tutorial shows how to implement Restful file upload/download APIs using Spring Boot 2.2.6 (Spring Web MVC only).

Part 1: Environment

JDK 1.8

Spring Boot 2.2.6 (Web MVC)

Maven 3.5+

IntelliJ IDEA 2019.2

Postman 7.23.0

Part 2: Features

Client uploads files to server.

Upload size limited to 50 MB.

Download files via link.

List uploaded files with name and download URL.

Part 3: Project Structure

config/FileUploadConfiguration.java – cleans old files on startup.

controller/FileUploadController.java – handles upload, download, list requests.

exception/FileUploadExceptionAdvice.java – global exception handling.

service/FileStorageService.java – interface for storage operations.

service/impl/FileStorageServiceImpl.java – implementation using java.nio.file.

valueobject/UploadFile.java – POJO for file name and URL.

valueobject/Message.java – POJO for response messages.

resources/application.yml (or application.properties) – configures max upload size.

pom.xml – Maven dependencies (spring-boot-starter-web).

Part 4: Creating the Spring Boot Project

Add the following Maven dependency:

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

Define the storage interface FileStorageService with methods init(), save(MultipartFile), load(String), load(), and clear(). Implement it in FileStorageServiceImpl using Files.createDirectory, Files.copy, UrlResource, and FileSystemUtils.deleteRecursively. The controller uses @RestController with @PostMapping("/upload"), @GetMapping("/files"), and @GetMapping("/files/{filename:.+}") to handle the respective operations.

Part 5: Configuring Upload Size

Set the maximum request and file size to 50 MB in application.yml or application.properties:

spring:
  servlet:
    multipart:
      max-request-size: 50MB
      max-file-size: 50MB

Part 6: Global Exception Handling

Handle MaxUploadSizeExceededException with a @ControllerAdvice class that returns a friendly error message.

Part 7: Initializing Storage

Implement CommandLineRunner in FileUploadConfiguration to call clear() and init() at startup.

Part 8: Running and Testing

Start the application via mvn spring-boot:run, IDE run button, main method, or java -jar. After startup a fileStorage directory is created. Use Postman to test:

POST /upload to upload a file (files larger than 50 MB trigger the size‑limit exception).

GET /files to retrieve the list of uploaded files.

GET /files/{filename} to download a specific file.

Responses include appropriate HTTP headers for file download.

Conclusion

The tutorial demonstrates a complete Spring Boot 2.2.6 solution for Restful file upload and download, including size limitation, global error handling, and testing with Postman.