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.

Java

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringBootFileHandlingApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringBootFileHandlingApplication.class, args);
    }

}

Step 4: Create the Controller Class

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

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); 
        
    }
}

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