Here is one use case for need of files stored on the cloud - the third party API you use takes URL as a parameter to process a picture :-)
I wanted to build a little game to communicate emotion long distance via BB8 toy, we saw it in the class, I found a perfect API that would give me coordinates of mouth, eyes, nose, etc, and then I use math equations to process the curvature of the mouth to detect the person's emotional state. (sometimes math does help!)
​https://www.kairos.com/docs/api/#face-recognition
I used the code below to store my files on heroku then pass to Kairos
​The video below shows the end result

storing files in postgres

Create your table in Postgres

CREATE TABLE FILES(filename text, file bytea);

Save file to Postgres:

package command;

import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.PreparedStatement;

import org.apache.tomcat.util.http.fileupload.IOUtils;

import connectionprovider.ConnectionProvider;

public class SaveFileToDBCommand {

	public void execute(String fileName, InputStream fis, long l) {

		try {
			ByteArrayOutputStream output = new ByteArrayOutputStream();
			IOUtils.copy(fis, output);
			byte[] filecontent = output.toByteArray();
			Connection connection = ConnectionProvider.getConnection();
			PreparedStatement stmt = connection
					.prepareStatement("INSERT INTO FILES VALUES (?, ?)");
			stmt.setString(1, fileName);
			stmt.setBytes(2, filecontent);
			stmt.executeUpdate();

		} catch (Exception e) {
			e.printStackTrace();
		}
	}

}

Retrieve the file from Postgres

package command;

import java.io.InputStream;
import java.net.URISyntaxException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import connectionprovider.ConnectionProvider;

public class GetFileFromPOSTGRESCommand {

	public InputStream execute(String filename) {

		Connection conn;
		try {
			conn = ConnectionProvider.getConnection();
			PreparedStatement stmt = conn
					.prepareStatement("SELECT FILE FROM FILES WHERE FILENAME=?");
			stmt.setString(1, filename);
			ResultSet rs = stmt.executeQuery();
	        if (rs != null) {
	            while (rs.next()) {
	                InputStream is = rs.getBinaryStream("file");
	                return is;
	            }
	            rs.close();
	        }    
		} catch (URISyntaxException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

		return null;
	}
}

Services:

	@GET
	@Path("download/{filename}")
	@Produces(MediaType.WILDCARD)
	public Response getFile(@PathParam("filename") String filename) {
		try {
			GetFileFromPOSTGRESCommand getFile = new GetFileFromPOSTGRESCommand();
			InputStream is = getFile.execute(filename);

			ResponseBuilder response = Response.ok((Object) is);
			response.header("Content-Disposition", "attachment; filename=\""
					+ filename + "\"");
			return response.build();
		} catch (Exception e) {
			return Response.status(404).entity(e.getMessage()).build();
		}
	}
	
	@GET
	@Path("inline/{filename}")
	@Produces("image/*")
	public Response renderFile(@PathParam("filename") String filename) {
		try {
			GetFileFromPOSTGRESCommand getFile = new GetFileFromPOSTGRESCommand();
			InputStream is = getFile.execute(filename);

			ResponseBuilder response = Response.ok((Object) is);
			response.header("Content-Disposition", "inline; filename=\""
					+ filename + "\"");
			return response.build();
		} catch (Exception e) {
			return Response.status(404).entity(e.getMessage()).build();
		}
	}

	
	@POST
	@Path("/upload/db")
	@Consumes(MediaType.MULTIPART_FORM_DATA)
	public Response uploadDBFile(
		@FormDataParam("file") InputStream uploadedInputStream,
		@FormDataParam("file") FormDataContentDisposition fileDetail) {
 
		SaveFileToDBCommand cmd = new SaveFileToDBCommand();
		cmd.execute(fileDetail.getFileName(), uploadedInputStream, fileDetail.getSize());
		return Response.status(200).build();
 
	}