Dropbox? On the EV3?

The first thing to realise is that I’m not going to show you how to install the Dropbox helper on your EV3. Instead we’re going to use the Dropbox Core Java SDK to connect our EV3 to your existing Dropbox account (free or pro, doesn’t matter) and then upload and download files into the account.

Dropbox is well known as a cloud file-sync service that ‘just works’. I’ve been using it for years, both as a pro and business user, and the software runs in the background, never complains and just gets on with the business of keeping all of your files in sync. Luckily Dropbox have extended the same simplicity to their SDK; I was amazing at just how easy it is to use the Java SDK in leJOs 0.9.0 to upload images captured from a webcam to my Dropbox account.

Step 1: Download the Dropbox Core API

Step 2: Create a new leJOS project in Eclipse

Step 3: Import the Dropbox Jar files from the SDK into your project

Step 4: Create a new Dropbox app

Step 5: Get the app key and app secret

Step 6: Copy the Dropbox JARs onto the EV3

Step 7: Authorise the EV3 to Dropbox, get the auth token

jrun -cp /home/lejos/programs/lib/dropbox-core-sdk-1.7.7.jar:/home/lejos/programs/lib/jackson-core-2.2.4.jar:GetAccessToken.jar GetAccessToken

Step 8: You’re done!

The code

Here's the code you need.

import com.dropbox.core.*;
import com.dropbox.core.json.JsonReader;
import java.io.*;
import java.util.Locale;
import java.util.logging.Level;
import java.util.logging.Logger;
import lejos.hardware.lcd.LCD;
/**
 * An example command-line application that runs through the web-based OAuth
 * flow (using {@link DbxWebAuth}).
 * 
 * By Mark Crosbie http://thinkbricks.net
 * Modified from the Dropbox tutorial code
 */
public class GetAccessToken {
	// The access token is saved in this file on the EV3 SDcard
	public static final String accessTokenFilename = "./access-token.json";
    public static void main(String[] args) throws IOException {
    	LCD.clear();
    	System.out.println("-- Get Dropbox auth token --");
    	System.out.println("1. Log into Dropbox and go to the App Console in your account");
    	System.out.println("2. Click on the app you created for the EV3");
    	System.out.print("3. Enter the App key value here: ");
        String appKey = new BufferedReader(new InputStreamReader(System.in)).readLine();
        if (appKey == null) {
            System.exit(1); return;
        }
        appKey = appKey.trim();
        System.out.println("");
        System.out.print("4. Enter the App secret value here: ");
        String appSecret = new BufferedReader(new InputStreamReader(System.in)).readLine();
        if (appSecret == null) {
            System.exit(1); return;
        }
        appSecret = appSecret.trim();
        System.out.println("");
    	System.out.println("5. Starting Dropbox auth flow");
    	DbxAppInfo appInfo = new DbxAppInfo(appKey, appSecret);
        String userLocale = Locale.getDefault().toString();
        DbxRequestConfig config = new DbxRequestConfig("JavaTutorial/1.0", userLocale);
        DbxWebAuthNoRedirect webAuth = new DbxWebAuthNoRedirect(config, appInfo);
        // Run through Dropbox API authorization process
        String authorizeUrl = webAuth.start();
        System.out.println("6. Go to " + authorizeUrl);
        System.out.println("7. Click \"Allow\" (you might have to log in first).");
        System.out.println("8. Copy the authorization code.");
        System.out.print("9. Enter the authorization code here: ");
        String code = new BufferedReader(new InputStreamReader(System.in)).readLine();
        if (code == null) {
            System.exit(1); return;
        }
        code = code.trim();
        DbxAuthFinish authFinish;
        try {
            authFinish = webAuth.finish(code);
        }
        catch (DbxException ex) {
            System.err.println("Error in DbxWebAuth.start: " + ex.getMessage());
            System.exit(1); return;
        }
        System.out.println("10. Authorization complete.");
        System.out.println("- User ID: " + authFinish.userId);
        System.out.println("- Access Token: " + authFinish.accessToken);
        // Save auth information to output file.
        DbxAuthInfo authInfo = new DbxAuthInfo(authFinish.accessToken, appInfo.host);
        try {
            DbxAuthInfo.Writer.writeToFile(authInfo, accessTokenFilename);
            System.out.println("Saved authorization information to \"" + accessTokenFilename + "\".");
        }
        catch (IOException ex) {
            System.err.println("Error saving to : " + ex.getMessage());
            System.err.println("Dumping to stderr instead:");
            DbxAuthInfo.Writer.writeToStream(authInfo, System.err);
            System.exit(1); return;
        }
    }
}