Spring Boot - File Handling

File handling in Spring Boot refers to the process of uploading, storing, retrieving, and downloading files through REST APIs in a web application. Spring Boot provides built-in support for file upload using MultipartFile and simplifies file operations through its integration with the Spring Web module.

• Enables file upload and download functionality in web applications using REST APIs.
• Uses MultipartFile to handle files received through multipart/form-data requests.
• Allows applications to store files on the server and retrieve them when required.

Implementation of the Application

Now, let us implement a Spring Boot application to demonstrate file upload and download functionality step by step.

Step 1: Create a Spring Boot Project

Generate a project using Spring Initializr and fill in the details:

• Project: Maven
• Language: Java
• Spring Boot Version: Latest stable version
• Group: com.example
• Artifact: springboot-file-handling
• Packaging: Jar
• Java Version: 17 (or higher)
• Dependencies: Spring Web

Click Generate to download the starter project.

Step 2: Configure File Upload Properties

Add the following configuration in application.properties to enable multipart file uploads.

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

Explanation:

• spring.servlet.multipart.enabled
  Enables multipart file upload functionality.
• spring.servlet.multipart.max-file-size
  Specifies the maximum allowed size for an uploaded file.
• spring.servlet.multipart.max-request-size
  Specifies the maximum size allowed for a multipart request.

Step 3: Create the Main Class

Create the main class to run the Spring Boot application.

Step 4: Create the Controller Class

Create a FileController class to handle file upload, download, and listing operations.

Step 5: Run the Application

Run the main class.
The Spring Boot application will start on:

http://localhost:8080

Step 6: Test the APIs Using Postman

1. Upload File API

URL

POST http://localhost:8080/upload

In order to upload a file we need to hit http://localhost:8080/upload in Postman with form data as shown below:

On Successful upload of the file, we can see the file in the Uploads folder as below:

2. Get list of Files API

We need to hit http://localhost:8080/getFiles in postman to get a list of filenames that have been uploaded.

URL

GET http://localhost:8080/getFiles

3. Download File API

URL

GET http://localhost:8080/download/{filename}

In order to download a file we need to hit http://localhost:8080/download/{filename} in postman as shown below.

The file can be downloaded in Postman using Save Response → Save to a File, or directly from the browser using the download URL. If the file does not exist, the API returns "File Not Found" with HTTP 404.