Recommended way / order to read data from a webservice, parse that data and insert it in a SQLite db
I'm one to start mentioning that I'm totally new to Android, I've just finished reading a quick, introductory book and now I have to implement my very first app. This app is going to be use to take orders. Among all the data I'm going to store in a local db, two tables are the most important: Customers and Articles, being the latter the largest of all the tables (aprox 20000 records) One of the main process in my app, fetches all the data that my app need to work off-line when the user press a button that starts the daily operations on the device.
Well, the process consists of the following steps :
a. Read a restful service to retrieve the Customers Data
b. Parse the response to Json Objects
c. Insert those customers to the Customers Table
d. Read a restful service to retrieve the Articles Data
e. Parse the response to Json Objects
f. Insert those articles to the Articles Table
This is what I've planned to do:
- Write a helper class that handles all the HTTP GET requests. Then call this class whenever I need to download all the Customers and Articles data
- Since all this process might take a lot of time, I need to do it the background. So based on some suggestions I'm going to put all this code inside a Bound Service.
- While all this long processing is taking place in the background I'll have to show some sort of indicator (a ProgressDialog) This is the reason I opted for using a Bound Service
Though I think I've got the general idea of how to do most of these thing separately, I think that putting the all together is quite a different story.
So these are the questions I've got now that I have to put the puzzle together:
- Do you think the order in which I'm executing all the 6 steps of the process described is correct / efficient? If you had to make some changes, what would you change?
- If the activity that started the service is explicitly cancelled or is hidden by another activity, the service has to have a way to let the user know that the process has finished. How could I implement that?
- Is it possible/ recommended to write to the SQLite DB within the service? Is it the same as when I do so within an activity?
- In J2ME I've done something similar, and when I put something like the 6 steps I mentioned above all of them are executed sequentially, that is , one after the other. Is it the same in Android?
I hope I'm not asking too many questions. I just put them together because they are all related.
Basically in this question I'm not asking for working code ( though it'd be OK if you could provide some sample code) What I'm really after is some suggestions, some guidance. Something like "Hey, I think this might help you with point number 3" or "You might find this article useful", "I think you'd better off using this instead of that". That kind of thing.
I decided to come to you because you're the experts and I really need someone to put me in the right direction.
Thank you very much.
P.S. Please do not close this question, if your think I need to change something just let me know and I'll do it.
Solution 1:
I decided to come to you because you're the experts
first i am not expert and also i am not knowledgeable you can find more expert people than me but this is my opinion hope to give you some help.
first of all forget to use AsyncTask to download because it must be used for short background jobs not like yours i think the amount of file you want to download is pretty large.(i think so)
check downloadmanager of google to see how it works it may help you.
http://developer.android.com/reference/android/app/DownloadManager.html
http://blog.vogella.com/2011/06/14/android-downloadmanager-example/
if you want to use service use unbound service because you do not want the service to be destroyed by android or user when the user close the apps do you? i think you want to get your data any way.
in order to be efficient i recommend these steps:
a. Read a restful service to retrieve the Customers Data
b. when you get Customer data do :
create another service or thread to Read a restful service to retrieve the Articles Data
Parse the response to Json Objects on your old service or thread
now you have 2 services or threads that run concurrently so follow the steps that obvious insert parse and so, on each service or thread.
why do not i combine a and d? because i think user do not like to wait much time behind download progress bar.
in order to insert your data to database use transaction and i recommend you use:
http://greendao-orm.com/
it is more efficient ORM than others for database and you get free from db implementation.
If the activity that started the service is explicitly cancelled or is hidden by another activity, the service has to have a way to let the user know that the process has finished. How could I implement that?
use notification:
http://developer.android.com/training/notify-user/build-notification.html
http://www.tutorialspoint.com/android/android_notifications.htm
http://www.vogella.com/tutorials/AndroidNotifications/article.html
While all this long processing is taking place in the background I'll have to show some sort of indicator (a ProgressDialog) This is the reason I opted for using a Bound Service`
how can I update the UI from an Unbound Service?`
Use a LocalBroadCastManager, or in general BroadCastReciever
Android update activity UI from service
In J2ME I've done something similar, and when I put something like the 6 steps I mentioned above all of them are executed sequentially, that is , one after the other. Is it the same in Android?
this is depends on your steps, if you follow my idea you run concurrently and if you run your idea you will run sequentially.
Good Luck.
Solution 2:
I did something like yours.
In first step I get data from webservice in HTTP GET of POST method using AsyncTask like this:
public class GetService extends AsyncTask<String, String, String> {
private String mRestUrl;
private ServiceCallback mCallback;
private final HttpClient Client = new DefaultHttpClient();
private String Content;
private String url;
private String Error;
private ProgressDialog barProgressDialog;
private ProgressDialog Dialog;
public GetService(String restUrl, ServiceCallback callback) {
this.mRestUrl = restUrl;
this.mCallback = callback;
this.url = restUrl;
Dialog = new ProgressDialog(AppContext.CurrentContext);
}
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected String doInBackground(String... urls) {
Content = null;
BufferedReader reader = null;
try {
StringBuilder builder = new StringBuilder();
HttpClient client = new DefaultHttpClient();
HttpGet get = new HttpGet(this.url);
HttpResponse response = client.execute(get);
int status = response.getStatusLine().getStatusCode();
if (status == 200) // sucess
{
HttpEntity e = response.getEntity();
// String data = EntityUtils.toString(e);
InputStream content = e.getContent();
reader = new BufferedReader(new InputStreamReader(content));
String line;
while ((line = reader.readLine()) != null) {
builder.append(line);
}
Content = builder.toString();
} else if (status == 401) {
return "-Auth Failed Error Code 400";
} else {
return "-Error Code: " + status;
}
} catch (Exception ex) {
Error = ex.getMessage();
} finally {
Dialog.dismiss();
try {
reader.close();
}
catch (Exception ex) {
ex.printStackTrace();
}
}
return Content;
}
@Override
protected void onPostExecute(String result) {
try {
GetService.this.get(20000, TimeUnit.MILLISECONDS);
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
} catch (TimeoutException e) {
e.printStackTrace();
}
mCallback.onTaskComplete(result);
super.onPostExecute(result);
}
}
and my callback class is:
public abstract class ServiceCallback{
public abstract void onTaskComplete(String result);
}
I call AsyncTask in my code everywhere I want to get data from webservice:
new GetService(url, new ServiceCallback() {
public void onTaskComplete(String response) {
// Parse Response of WebService
}
}).execute();
In second step I Parse response of WebService in onTaskComplete method using json helper Libraries like Gson or Jackson. for example in jackson:
List<YourClass> data = new ObjectMapper()
.readValue(
response,
new TypeReference<List<YourClass>>() {
});
At the end I store Data in Database. for connecting to DB I Prefer to use GreenDao as my ORM. In this way storin data in DB can be done in one line code like this:
//after converting json to object
YourORMDaoClass.insertOrReplaceInTx(data);
To Use GreenDao ORM this link is very helpful;
Solution 3:
Do you think the order in which I'm executing all the 6 steps of the process described is correct / efficient? If you had to make some changes, what would you change?
It depends. If this data is related and cannot exists without each other then you should change the order like this:
a. Read a restful service to retrieve the Customers Data
b. Parse the response to Json Objects
d. Read a restful service to retrieve the Articles Data
e. Parse the response to Json Objects
c. Insert those customers to the Customers Table
f. Insert those articles to the Articles Table
Steps c and f should be combined in transaction.
Otherwise, the order does not matter. If data is not related then separating these processes and running them in sequence might be a good idea.
If the activity that started the service is explicitly cancelled or is hidden by another activity, the service has to have a way to let the user know that the process has finished. How could I implement that?
I suggest to start with implementation of the IntentService class. It handles for you background thread and works like a queue of events where single Intent delivers a data to process.
Actually you could implement one of the patterns presented by Google on one of their IO conferences. I have implemented an option A shown on the video. It works for me really well. The trick is that using ContentProvider from the background automatically updates UI which listen for changes thanks to CursorAdapter.
To update UI progress you can use LocalBroadcastManager or event bus libraries e.g. Otto.
You can also extend your tables and store status and progress, updating tables would automatically update UI as well, just keep in mind that these updates should be rare e.g. control in the service background how often table progress is updated calculating the progress first and checking with service local variable if it's changed.
In case your app is in the background, post status notification. User should be able to navigate back to your app clicking on the notification.
Is it possible/ recommended to write to the SQLite DB within the service? Is it the same as when I do so within an activity?
You can do it within the Service. Actually, if you follow the pattern I have mentioned above, you would do it in the Processor tier on the background service thread.
In J2ME I've done something similar, and when I put something like the 6 steps I mentioned above all of them are executed sequentially, that is , one after the other. Is it the same in Android?
It's completely up to you how communication with the server will work. If you decide to use IntentService class then it will work in a sequence which is not a bad idea on Android. On the other hand you may extend Service class directly and implement own thread executor with a thread pool. You can also have dedicated IntentService classes for unrelated operations.
I also recommend to read lessons:
- Transferring Data Without Draining the Battery
- Transferring Data Using Sync Adapters
If you don't want to play directly with HTTP connection implementation then consider using Retrofit or Volley
If you just need JSON parsers then these 2 are the best:
- GSON
- Jackson