[android] Sync data between Android App and webserver

I want to sync data (such as db record, media) between an Android App and a Server. If you've seen Evernote or similar Applications, you certainly understand what I mean.

I have some question (imagine we want to sync DB records):

1. Every user has a part of server space for himself (such as Evernote or Dropbox). Maybe the user creates new records by cellphone and creates new records in server. How can I match these records together? If there are records with same ID What algorithms do you suggest me?

2. Except JSON, Are there any way for send data between cellphone device and server?

3. If SyncAdapter and ContentProvider can solve my problems, please explain exactly for me. (If you could offer some samples or tutorials to me OR Any advice or keywords to help broaden/guide my search would be appreciated as well).

If we think about today, accepted answer is too old. As we know that we have many new libraries which can help you to make this types of application.

You should learn following topics that will helps you surely:

• SyncAdapter: The sync adapter component in your app encapsulates the code for the tasks that transfer data between the device and a server. Based on the scheduling and triggers you provide in your app, the sync adapter framework runs the code in the sync adapter component.

• Realm: Realm is a mobile database: a replacement for SQLite & Core Data.

• Retrofit Type-safe HTTP client for Android and Java by Square, Inc. Must Learn a-smart-way-to-use-retrofit

And your sync logic for database like: How to sync SQLite database on Android phone with MySQL database on server?

Best Luck to all new learner. :)

I would suggest using a binary webservice protocol similar to Hessian. It works very well and they do have a android implementation. It might be a little heavy but depends on the application you are building. Hope this helps.

one way to accomplish this to have a server side application that waits for the data. The data can be sent using HttpRequest objects in Java or you can write your own TCP/IP data transfer utility. Data can be sent using JSON format or any other format that you think is suitable. Also data can be encrypted before sending to server if it contains sensitive information. All Server application have to do is just wait for HttpRequests to come in and parse the data and store it anywhere you want.

For example, you want to sync table todoTable from MySql to Sqlite

First, create one column name version (type INT) in todoTable for both Sqlite and MySql

Second, create a table name database_version with one column name currentVersion(INT)

In MySql, when you add a new item to todoTable or update item, you must upgrade the version of this item by +1 and also upgrade the currentVersion

In Android, when you want to sync (by manual press sync button or a service run with period time):

You will send the request with the Sqlite currentVersion (currently it is 1) to server.
Then in server, you find what item in MySql have version value greater than Sqlite currentVersion(1) then response to Android (in this example the item 3 with version 2 will response to Android)

In SQLite, you will add or update new item to todoTable and upgrade the currentVersion

Look at parseplatform.org. it's opensource project.

(As well as you can go for commercial package available at back4app.com.)

It is a very straight forward and user friendly server side database service that gives a great android client side API

@Grantismo provides a great explanation on the overall. If you wish to know who people are actually doing this things i suggest you to take a look at how google did for the Google IO App of 2014 (it's always worth taking a deep look at the source code of these apps that they release. There's a lot to learn from there).

Here's a blog post about it: http://android-developers.blogspot.com.br/2014/09/conference-data-sync-gcm-google-io.html

Essentially, on the application side: GCM for signalling, Sync Adapter for data fetching and talking properly with Content Provider that will make things persistent (yeah, it isolates the DB from direct access from other parts of the app).

Also, if you wish to take a look at the 2015's code: https://github.com/google/iosched

@Grantismo gives a great overview of Android sync components.

SyncManagerAndroid library provides a simple 2-way sync implementation to plug into the Android Sync framework (AbstractThreadedSyncAdapter.OnPerformSync).

https://github.com/sschendel/SyncManagerAndroid

If you write this yourself these are some of the points to keep in mind

Proper authentication between the device and the Sync Server

A sync protocol between the device and the server. It will usually go in 3 phases, authentication, data exchange, status exchange (which operations worked and which failed)

Pick your payload format. I suggest SyncML based XML mixed with JSON based format to represent the actual data. So SyncML for the protocol, and JSON for the actual data being exchanged. Using JSON Array while manipulating the data is always preferred as it is easy to access data using JSON Array.

Keeping track of data changes on both client and server. You can maintain a changelog of ids that change and pick them up during a sync session. Also, clear the changelog as the objects are successfully synchronized. You can also use a boolean variable to confirm the synchronization status, i.e. last time of sync. It will be helpful for end users to identify the time when last sync is done.

Need to have a way to communicate from the server to the device to start a sync session as data changes on the server. You can use C2DM or write your own persistent tcp based communication. The tcp approach is a lot seamless

A way to replicate data changes across multiple devices

And last but not the least, a way to detect and handle conflicts

Hope this helps as a good starting point.