[Android] Restful API service


Answers

Developing Android REST client applications has been an awesome resource for me. The speaker does not show any code, he just goes over design considerations and techniques in putting together a rock solid Rest Api in android. If your a podcast kinda person or not, I'd recommend giving this one at least one listen but, personally I've listened to it like 4 or five times thus far and I'm probably going to listen to it again.

Developing Android REST client applications
Author: Virgil Dobjanschi
Description:

This session will present architectural considerations for developing RESTful applications on the Android platform. It focuses on design patterns, platform integration and performance issues specific to the Android platform.

And there are so many considerations I really hadn't made in the first version of my api that I've had to refactor

Question

I'm looking to make a service which I can use to make calls to a web-based REST API.

Basically I want to start a service on app init then I want to be able to ask that service to request a url and return the results. In the meantime I want to be able to display a progress window or something similar.

I've created a service currently which uses IDL, I've read somewhere that you only really need this for cross app communication, so think these needs stripping out but unsure how to do callbacks without it. Also when I hit the post(Config.getURL("login"), values) the app seems to pause for a while (seems weird - thought the idea behind a service was that it runs on a different thread!)

Currently I have a service with post and get http methods inside, a couple of AIDL files (for two way communication), a ServiceManager which deals with starting, stopping, binding etc to the service and I'm dynamically creating a Handler with specific code for the callbacks as needed.

I don't want anyone to give me a complete code base to work on, but some pointers would be greatly appreciated.

Code in (mostly) full:

public class RestfulAPIService extends Service  {

final RemoteCallbackList<IRemoteServiceCallback> mCallbacks = new RemoteCallbackList<IRemoteServiceCallback>();

public void onStart(Intent intent, int startId) {
    super.onStart(intent, startId);
}
public IBinder onBind(Intent intent) {
    return binder;
}
public void onCreate() {
    super.onCreate();
}
public void onDestroy() {
    super.onDestroy();
    mCallbacks.kill();
}
private final IRestfulService.Stub binder = new IRestfulService.Stub() {
    public void doLogin(String username, String password) {

        Message msg = new Message();
        Bundle data = new Bundle();
        HashMap<String, String> values = new HashMap<String, String>();
        values.put("username", username);
        values.put("password", password);
        String result = post(Config.getURL("login"), values);
        data.putString("response", result);
        msg.setData(data);
        msg.what = Config.ACTION_LOGIN;
        mHandler.sendMessage(msg);
    }

    public void registerCallback(IRemoteServiceCallback cb) {
        if (cb != null)
            mCallbacks.register(cb);
    }
};

private final Handler mHandler = new Handler() {
    public void handleMessage(Message msg) {

        // Broadcast to all clients the new value.
        final int N = mCallbacks.beginBroadcast();
        for (int i = 0; i < N; i++) {
            try {
                switch (msg.what) {
                case Config.ACTION_LOGIN:
                    mCallbacks.getBroadcastItem(i).userLogIn( msg.getData().getString("response"));
                    break;
                default:
                    super.handleMessage(msg);
                    return;

                }
            } catch (RemoteException e) {
            }
        }
        mCallbacks.finishBroadcast();
    }
    public String post(String url, HashMap<String, String> namePairs) {...}
    public String get(String url) {...}
};

A couple of AIDL files:

package com.something.android

oneway interface IRemoteServiceCallback {
    void userLogIn(String result);
}

and

package com.something.android
import com.something.android.IRemoteServiceCallback;

interface IRestfulService {
    void doLogin(in String username, in String password);
    void registerCallback(IRemoteServiceCallback cb);
}

and the service manager:

public class ServiceManager {

    final RemoteCallbackList<IRemoteServiceCallback> mCallbacks = new RemoteCallbackList<IRemoteServiceCallback>();
    public IRestfulService restfulService;
    private RestfulServiceConnection conn;
    private boolean started = false;
    private Context context;

    public ServiceManager(Context context) {
        this.context = context;
    }

    public void startService() {
        if (started) {
            Toast.makeText(context, "Service already started", Toast.LENGTH_SHORT).show();
        } else {
            Intent i = new Intent();
            i.setClassName("com.something.android", "com.something.android.RestfulAPIService");
            context.startService(i);
            started = true;
        }
    }

    public void stopService() {
        if (!started) {
            Toast.makeText(context, "Service not yet started", Toast.LENGTH_SHORT).show();
        } else {
            Intent i = new Intent();
            i.setClassName("com.something.android", "com.something.android.RestfulAPIService");
            context.stopService(i);
            started = false;
        }
    }

    public void bindService() {
        if (conn == null) {
            conn = new RestfulServiceConnection();
            Intent i = new Intent();
            i.setClassName("com.something.android", "com.something.android.RestfulAPIService");
            context.bindService(i, conn, Context.BIND_AUTO_CREATE);
        } else {
            Toast.makeText(context, "Cannot bind - service already bound", Toast.LENGTH_SHORT).show();
        }
    }

    protected void destroy() {
        releaseService();
    }

    private void releaseService() {
        if (conn != null) {
            context.unbindService(conn);
            conn = null;
            Log.d(LOG_TAG, "unbindService()");
        } else {
            Toast.makeText(context, "Cannot unbind - service not bound", Toast.LENGTH_SHORT).show();
        }
    }

    class RestfulServiceConnection implements ServiceConnection {
        public void onServiceConnected(ComponentName className, IBinder boundService) {
            restfulService = IRestfulService.Stub.asInterface((IBinder) boundService);
            try {
            restfulService.registerCallback(mCallback);
            } catch (RemoteException e) {}
        }

        public void onServiceDisconnected(ComponentName className) {
            restfulService = null;
        }
    };

    private IRemoteServiceCallback mCallback = new IRemoteServiceCallback.Stub() {
        public void userLogIn(String result) throws RemoteException {
            mHandler.sendMessage(mHandler.obtainMessage(Config.ACTION_LOGIN, result));

        }
    };

    private Handler mHandler;

    public void setHandler(Handler handler) {
        mHandler = handler;
    }
}

Service init and bind:

// this I'm calling on app onCreate
servicemanager = new ServiceManager(this);
servicemanager.startService();
servicemanager.bindService();
application = (ApplicationState)this.getApplication();
application.setServiceManager(servicemanager);

service function call:

// this lot i'm calling as required - in this example for login
progressDialog = new ProgressDialog(Login.this);
progressDialog.setMessage("Logging you in...");
progressDialog.show();

application = (ApplicationState) getApplication();
servicemanager = application.getServiceManager();
servicemanager.setHandler(mHandler);

try {
    servicemanager.restfulService.doLogin(args[0], args[1]);
} catch (RemoteException e) {
    e.printStackTrace();
}

...later in the same file...

Handler mHandler = new Handler() {
    public void handleMessage(Message msg) {

        switch (msg.what) {
        case Config.ACTION_LOGIN:

            if (progressDialog.isShowing()) {
                progressDialog.dismiss();
            }

            try {
                ...process login results...
                }
            } catch (JSONException e) {
                Log.e("JSON", "There was an error parsing the JSON", e);
            }
            break;
        default:
            super.handleMessage(msg);
        }

    }

};






There is another approach here which basically helps you to forget about the whole management of the requests. It is based on an async queue method and a callable/callback based response. The main advantage is that by using this method you'll be able to make the whole process (request, get and parse response, sabe to db) completely transparent for you. Once you get the response code the work is already done. After that you just need to make a call to your db and you are done. It helps as well with the problematic of what happens when your activity is not active. What will happen here is that you'll have all your data saved in your local database but the response won't be processed by your activity, that's the ideal way.

I wrote about a general approach here http://ugiagonzalez.com/2012/07/02/theres-life-after-asynctasks-in-android/

I'll be putting specific sample code in upcoming posts. Hope it helps, feel free to contact me for sharing the approach and solving potential doubts or issues.







Note that the solution from Robby Pond is somehow lacking: in this way you only allow todo one api call at a time since the IntentService only handles one intent at a time. Often you want to perform parallel api calls. If you want todo this you have to extend Service instead of IntentService and create your own thread.




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