How do you implement file upload and download in REST APIs with Spring Boot?

Table of Contents

• Introduction
• File Upload in Spring Boot
  • 1. Enable Multipart Configuration
    • In application.properties:
  • 2. Create the File Upload Controller
    • Example: File Upload Controller
  • 3. Test the File Upload Endpoint
    • CURL Example:
• File Download in Spring Boot
  • 1. Create the File Download Controller
    • Example: File Download Controller
  • 2. Test the File Download Endpoint
    • CURL Example:
• Practical Example for Both File Upload and Download
  • • Complete Example: FileController.java
• Conclusion

Introduction

Handling file uploads and downloads is a common requirement in modern web applications. Spring Boot, with its simplicity and flexibility, provides easy ways to implement these features in REST APIs. This guide covers how to implement file upload and download in a Spring Boot application, providing code examples for both scenarios. You will learn how to handle multipart files, store them, and serve them for download using Spring Boot.

File Upload in Spring Boot

1. Enable Multipart Configuration

To enable file upload functionality, first ensure that your Spring Boot application is configured to handle multipart file uploads. This can be done in the application.properties or application.yml file.

In application.properties:

These properties configure the maximum file size for uploads and enable multipart support in the application.

2. Create the File Upload Controller

You can create a REST controller to handle file upload requests. The @RequestPart annotation is used to bind the file to a method parameter.

Example: File Upload Controller

In this controller:

• The @RequestParam("file") binds the uploaded file to the MultipartFile parameter.
• The transferTo() method stores the file in a specified directory on the server.

3. Test the File Upload Endpoint

You can test this API endpoint using Postman or CURL. For example, a POST request like this would upload a file:

CURL Example:

File Download in Spring Boot

1. Create the File Download Controller

For file download, you can create a controller method that reads the file from the storage directory and returns it as a response.

Example: File Download Controller

In this controller:

• The @PathVariable binds the file name from the URL to the fileName parameter.
• The file is read from the server using Files.readAllBytes(), and the response is returned with the content and the appropriate Content-Disposition header for file download.

2. Test the File Download Endpoint

To download a file, make a GET request with the file name:

CURL Example:

This will download test-file.txt from the server.

Practical Example for Both File Upload and Download

Complete Example: FileController.java

Conclusion

Spring Boot provides a simple yet powerful way to handle file uploads and downloads in REST APIs. By using the MultipartFile for file uploads and returning files as byte arrays for downloads, you can easily implement these functionalities. Ensure that the proper configurations for file size and multipart support are set in your application.properties to handle large files efficiently.