GPS devices comunication functionality with server

Question

Hi i want to implement gps devices communication functionality in android devices but i don't know how these devices communicate with server that uses these devices data and save these data on server.I have to question about these devices
1-Can server connect these devices and get data and save data on server? Or these devices connect to server and send data to server.
this question is important for me because i want to write application for android devices that simulate gps devices functionality on android devices!
2:I research about how to connect from server to android devices and get information about mqtt! can i connect from server to android devices with mqtt?
for simulating these devices functionality on android devices on need to know which of server or device connect to other and send data?

Answer 1

First, you need to get the location position on the device, and then send it to your server, so you can show this information. Being pragmatic with code, you will need to get the location on the device with something like:

LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
locationManager.requestLocationUpdates("gps", 60000, 0, locationListener);

private final LocationListener locationListener = new LocationListener() {
        public void onLocationChanged(Location location) {
            // Here you have both location.getLatitude() and location.getLongitude()
        }
        public void onProviderDisabled(String provider){}   
        public void onProviderEnabled(String provider) {}
        public void onStatusChanged(String provider, int status, Bundle extras) {}
};

for more information regarding location on Android refer to the official documentation on User Location.

When you are done with the location part, you can start sending it to your server. Consider to use JSON for this.

Let's consider you have a String line with "latitudelongitude", you would need to build the JSON object first:

public JSONObject buildJSONObject(String line) {
        String[] toJson = line.split(" ");
        JSONObject object = new JSONObject();
        try {
            object.put("latitude", toJson[0]);
            object.put("longitude", toJson[1]);
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return object;
}

And then you would send it to the server with something like this:

public boolean sendTraceLineToServer(JSONObject line) {
    // The mock server IP is 10.0.2.2, just for testing purposes
    // This server receives a JSON with format {"location":{"latitude":xx.xx, "longitude":yy.yy}}
    HttpPost httpPost = new HttpPost("http://10.0.2.2:3000/locations");
    DefaultHttpClient client = new DefaultHttpClient();
    JSONObject holder = new JSONObject();

    boolean sent = false; 

    try {
        holder.put("location", line);

        StringEntity se = new StringEntity(holder.toString());
        httpPost.setEntity(se);
        httpPost.setHeader("Content-Type","application/json");
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (JSONException e) {
        e.printStackTrace();
    }

    HttpResponse response = null;

    try {
        response = client.execute(httpPost);
        sent = true;
    } catch (ClientProtocolException e) {
        e.printStackTrace();
        Log.e("ClientProtocol",""+e);
    } catch (IOException e) {
        e.printStackTrace();
        Log.e("IO",""+e);
    }

    HttpEntity entity = response.getEntity();

    if (entity != null) {
        try {
            entity.consumeContent();
        } catch (IOException e) {
            Log.e("IO E",""+e);
            e.printStackTrace();
        }
    }
    return sent;
}

Here you have more examples on how to post JSON to a server.

On the server, on my case I wrote it in Rails, I create a method to receive the JSON as simple as:

# POST /locations
# POST /locations.xml

def create
    @location = Location.new(params[:location])
    respond_to do |format|
      if @location.save
        format.json { render :json => @location, :status => :created, :location => @location }
      else
        format.json { render :json => @location.errors, :status => :unprocessable_entity }
      end
    end
  end

And that is it, location on the device, sending it using HTTP with JSON, and receiving on the example Rails server.