MainActivity.java

/*
 * Copyright (c) 2013 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 
 
 
 JSON EXAMPLE
 
[
    {
        "name": "John Doe",
        "latlng": [
            62.457434,
            17.349869
        ],
        "population": "123"
    },
    {
        "name": "Jane Doe",
        "latlng": [
            62.455102,
            17.345599
        ],
        "population": "132"
    },
    {
        "name": "James Bond",
        "latlng": [
            62.458287,
            17.356306
        ],
        "population": "123"
    }
] 
 */

package com.example.google.maps.demo;

import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.util.Log;

import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

/**
 * @author saxman
 */
public class MainActivity extends FragmentActivity {
    private static final String LOG_TAG = "ExampleApp";

    private static final String SERVICE_URL = "YOUR DRIVE SERVICE URL";

    protected GoogleMap map;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        setUpMapIfNeeded();
    }

    @Override
    protected void onResume() {
        super.onResume();
        setUpMapIfNeeded();
    }

    private void setUpMapIfNeeded() {
        if (map == null) {
            map = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map))
                    .getMap();
            if (map != null) {
                setUpMap();
            }
        }
    }

    private void setUpMap() {
        // Retrieve the city data from the web service
        // In a worker thread since it's a network operation.
        new Thread(new Runnable() {
            public void run() {
                try {
                    retrieveAndAddCities();
                } catch (IOException e) {
                    Log.e(LOG_TAG, "Cannot retrive cities", e);
                    return;
                }
            }
        }).start();
    }
    
    protected void retrieveAndAddCities() throws IOException {
        HttpURLConnection conn = null;
        final StringBuilder json = new StringBuilder();
        try {
            // Connect to the web service
            URL url = new URL(SERVICE_URL);
            conn = (HttpURLConnection) url.openConnection();
            InputStreamReader in = new InputStreamReader(conn.getInputStream());

            // Read the JSON data into the StringBuilder
            int read;
            char[] buff = new char[1024];
            while ((read = in.read(buff)) != -1) {
                json.append(buff, 0, read);
            }
        } catch (IOException e) {
            Log.e(LOG_TAG, "Error connecting to service", e);
            throw new IOException("Error connecting to service", e);
        } finally {
            if (conn != null) {
                conn.disconnect();
            }
        }

        // Create markers for the city data.
        // Must run this on the UI thread since it's a UI operation.
        runOnUiThread(new Runnable() {
            public void run() {
                try {
                    createMarkersFromJson(json.toString());
                } catch (JSONException e) {
                    Log.e(LOG_TAG, "Error processing JSON", e);
                }
            }
        });
    }
    
    void createMarkersFromJson(String json) throws JSONException {
        // De-serialize the JSON string into an array of city objects
        JSONArray jsonArray = new JSONArray(json);
        for (int i = 0; i < jsonArray.length(); i++) {
            // Create a marker for each city in the JSON data.
            JSONObject jsonObj = jsonArray.getJSONObject(i);
            map.addMarker(new MarkerOptions()
                .title(jsonObj.getString("name"))
                .snippet(Integer.toString(jsonObj.getInt("population")))
                .position(new LatLng(
                        jsonObj.getJSONArray("latlng").getDouble(0),
                        jsonObj.getJSONArray("latlng").getDouble(1)
                 ))
            );
        }
    }
}

if i receive my json from a web service hourly how can i get my markers updated??

when I write my code use the onResume () and declare like you, because I errorn mark the beginning of the key

@MikaeloN you can add a checker that request the file every hour , or a method that listens to the json