File Upload/Download with SpringBoot and MongoDB

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Nerd For Tech

4 min readJun 1, 2021

File upload & Download with spring boot and mongoDB article cover

In this article, we will be creating a simple RESTful web service using SpringBoot and MongoDB. We will be using GridFS to store files.

What is GridFS?

GridFS is a specification for storing and retrieving files that exceed the BSON-document size limit of 16MB. (Source: MongoDB Manual)

GridFS divide the file into small parts called chunks and store them as separate documents. The default size of a chunk is 255KB.

GridFS uses two collections to store files.

fs.files - store file’s metadata.
fs.chunks - store binary chunks of the file.

We’ll start by creating the REST APIs for uploading and downloading and test them using Postman. Alright! Let’s get to it.

1. Creating a project

Visit https://start.spring.io to generate the application through Spring Initializr with the following dependencies. This should download a zip file which you need to extract and open in your IDE.

Spring Initializr to create a maven project

2. Spring Boot Properties

Following configurations must be provided in the application.properties file in the “resources” folder.

Following are the MongoDB properties:

spring.data.mongodb.port = 27017
spring.data.mongodb.host = localhost
spring.data.mongodb.database = uploads

server.port=8080

The default port for service is 8080. You can change the port if you want. Also You can add authentication if you have any.

You can also use MongoDB Atlas instead of running MongoDB on localhost. Use the following properties in your application.

Replace <passsword> with admin’s password and <database> with the database name.

spring.data.mongodb.uri=mongodb+srv://admin:<password>@cluster0.eypdh.mongodb.net/<database>?retryWrites=true&w=majority

In addition, the following properties should be added to allow file uploading.

spring.servlet.multipart.enabled = true
spring.servlet.multipart.max-file-size = 200MB
spring.servlet.multipart.max-request-size = 200MB

3. Defining Classes

Note that we are not defining a document class here since we will only upload a file and it will directly store in the GridFS Collection.

The following class will be used to return the necessary responses when downloading a file.

4. Creating the Service Class

This service class contains the service to store and retrieve a file from GridFS.

Storing a file

addFile() method will store the file in the database and returns the Object ID of the file.
You can add extra information to your file as metadata. As an example, I have added file size as additional information. But it is not a must.
To store the file you need to pass the following data to the store method in GridFsTemplate.

template.store(Inputstream content, filename, ContentType, metadata)

Retrieving a file

downloadFile() method is used to return a specific file from the database.
findOne method in GridFSTemplate will return the file that matches the query.
Then, we set the response and its content to an Object from LoadFile class we created in Step 1 and return it.
We need to set the file to a byte array. To convert the InputStream into a byte array we are using Apache Commons IO.
For that, you need to add the following dependency in your pom.xml file.

<dependency>
   <groupId>commons-io</groupId>
   <artifactId>commons-io</artifactId>
   <version>2.8.0</version>
</dependency>

5. Creating the Controller

The controller class consist of the REST APIs for uploading and downloading a file.

POST

To upload a file we use the POST method.
The upload() method accepts a MultipartFile type object here.

GET

The GET method takes the {id} as a path parameter to return a specific document.
By download() method, receive the LoadFile object first, and then map the necessary details to a Response Header to make it downloadable.

Note that we are returning the data as a ByteArrayResource.