Develop Reference

How to push notification to client when Firebase has a new entry?

I wonder if it's possible to send push notifications to android mobile devices whenever Firebase gets added a new child on specific entity.
For example, let's say there's an entity on Firebase called Tasks. Whenever a new task is added to that firebase collection the "child_added" event is fired and then, in some way, a push notification is sent to a mobile client.
The trigger is the child_added event. However, I'm not sure if is feasible sending push notification right from Firebase events.

You can make a very simple node.js server or a java servlet (based on your language preferences) then using firebase server sdk you can add childEventListener. When value changes you can use FCM to send push notifications using http protocol. I am using this in my app and it is very feasable and reliable.
Note: If you are using this flow for an android app then using java server sdk will be beneficial as it is almost similar to what you have on android.
EDIT: After getting some spotlight on this answer I thought to share some more info regarding same.
//example node.js server as seen on this official firebase blog
var firebase = require('firebase');
var request = require('request');
var API_KEY = "..."; // Your Firebase Cloud Server API key
firebase.initializeApp({
serviceAccount: ".json",
databaseURL: "https://.firebaseio.com/"
});
ref = firebase.database().ref();
function listenForNotificationRequests() {
var requests = ref.child('notificationRequests');
ref.on('child_added', function(requestSnapshot) {
var request = requestSnapshot.val();
sendNotificationToUser(
request.username,
request.message,
function() {
request.ref().remove();
}
);
}, function(error) {
console.error(error);
});
};
function sendNotificationToUser(username, message, onSuccess) {
request({
url: 'https://fcm.googleapis.com/fcm/send',
method: 'POST',
headers: {
'Content-Type' :' application/json',
'Authorization': 'key='+API_KEY
},
body: JSON.stringify({
notification: {
title: message
},
to : '/topics/user_'+username
})
}, function(error, response, body) {
if (error) { console.error(error); }
else if (response.statusCode >= 400) {
console.error('HTTP Error: '+response.statusCode+' - '+response.statusMessage);
}
else {
onSuccess();
}
});
}
// start listening
listenForNotificationRequests();
//example test java servlet which I made just to demonstrate this use case
#WebServlet("/TestServlet")
public class MainServlet extends HttpServlet {
* #see HttpServlet#HttpServlet()
*/
public MainServlet() {
super();
}
/**
* #see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// Get context and then relative path to saved json config file from
// firebase
ServletContext context = getServletContext();
String fullPath = context.getRealPath(FILE_PATH_FOR_JSON_SERVER_AUTH);
// Check if we actually got a file from above path
if (fullPath != null) {
} else {
}
// Setup connection to firebase database here
FirebaseOptions options = new FirebaseOptions.Builder().setServiceAccount(new FileInputStream(fullPath))
.setDatabaseUrl(FIREBASE_DATABSE_URL).build();
// Check to make sure we don't initialize firebase app each time webpage
// is refreshed
if (!exists) {
// If firebase app doesn't exist then initialize it here and set
// exists to true
FirebaseApp.initializeApp(options);
exists = true;
}
// Call this to begin listening *notify* node in firebase database for notifications
addNotificationListener(request, response);
}
/**
* #see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// Build apache httpclient POST request
HttpClient client = HttpClientBuilder.create().build();
HttpPost post = new HttpPost(ENDPOINT_URL);
//Get the required id stored in lastMsgId tree map here
if (!(chatLogs.getLastMsgIdTreeMap().isEmpty())) {
sendToID = chatLogs.getLastMsgIdTreeMap().firstKey();
lstmsg = chatLogs.getLastMsgIdTreeMap().get(sendToID);
}
//Set up a unique id with concatenating sendToID and lstmsg
uniqueID = sendToID + lstmsg;
//Set up a previous id to check with unique id. To avoid instant duplicate notifications
previousID = fcmHelper.getPreviousid();
// Check uniqueId and PreviousID beforeSending
if (!(uniqueID.equals(previousID))) {
fcmHelper.setPreviousid(uniqueID);
//Check if device token and user Id hashmap is not null
if (!(userLogs.getUserIdAndFcmTokenHashMap().isEmpty())) {
//Get the device token of sendTo Id here
deviceToken = userLogs.getUserIdAndFcmTokenHashMap().get(sendToID);
// Create JSON object for downstream data/notification
JSONObject mainNotificationJsonObj = new JSONObject();
JSONObject outerBaseJsonObj = new JSONObject();
try {
// Notification payload has 'title' and 'body' key
mainNotificationJsonObj.put(TITLE, NEW_MESSAGE_RECEIVED);
mainNotificationJsonObj.put(BODY, lstmsg);
mainNotificationJsonObj.put(NOTIFICATION_SOUND, NOTIFICATION_SOUND_TYPE_DEFAULT);
//mainNotificationJsonObj.put(TAG, fcmHelper.getFcmTagId());
System.out.println("This is sentBy id =" + fcmHelper.getFcmTagId());
// This will be used in case of both 'notification' or 'data' payload
outerBaseJsonObj.put(TO, deviceToken);
// Set priority of notification. For instant chat setting
// high will
// wake device from idle state - HIGH BATTERY DRAIN
outerBaseJsonObj.put(PRIORITY_KEY, PRIORITY_HIGH);
// Specify required payload key here either 'data' or
// 'notification'. We can even use both payloads in single
// message
outerBaseJsonObj.put(NOTIFICATION, mainNotificationJsonObj);
} catch (JSONException e) {
e.printStackTrace();
}
// Setup http entity with json data and 'Content-Type' header
StringEntity requestEntity = new StringEntity(outerBaseJsonObj.toString(),
ContentType.APPLICATION_JSON);
// Setup required Authorization header
post.setHeader(AUTHORIZATION, FIREBASE_SERVER_KEY);
// Pass setup entity to post request here
post.setEntity(requestEntity);
// Execute apache http client post response
HttpResponse fcmResponse = client.execute(post);
// Get status code from FCM server to debug error and success
System.out.println(RESPONSE_CODE + fcmResponse.getStatusLine().getStatusCode());
// Get response entity from FCM server and read throw lines
BufferedReader rd = new BufferedReader(new InputStreamReader(fcmResponse.getEntity().getContent()));
StringBuffer result = new StringBuffer();
String line = "";
while ((line = rd.readLine()) != null) {
result.append(line);
}
if (response != null) {
// Print out the response to webpage
PrintWriter out;
out = response.getWriter();
out.println(result);
System.out.println("This is Result - " + result);
}
} else {
//Abort this process if conditions not met
post.abort();
System.out.println(THIS_MSG_ALREADY_SENT);
}
}
}
/*
* This is the main method to be called to setup notifications listener on server startup
*/
private void addNotificationListener(HttpServletRequest request, HttpServletResponse response) {
//Initialize Value event listener
lastMsgListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot arg0) {
// Clear idLastMessagerecivedhash map if not null
if (lastMsgIdTreeMap != null) {
lastMsgIdTreeMap.clear();
}
//Get lastmsg to be sent as notification here
lstmsg = (String) arg0.child(LAST_MESSAGE).getValue();
//Get sendToID here
String sendToID = (String) arg0.child(SEND_TO).getValue();
//Get Sent by ID here
sentBy = (String) arg0.child(SENT_BY).getValue();
//Set fcmTag ID here
fcmHelper.setFcmTagId(sentBy);
//Check if lstmsg is not null
if (lstmsg != null) {
// Create lastmsgTimestampHashMap here
lastMsgIdTreeMap.put(sendToID, lstmsg);
}
//Check for null again
if (lastMsgIdTreeMap != null) {
chatLogs.setLastMsgIdTreeMap(lastMsgIdTreeMap);
}
try {
doPost(request, response);
} catch (ServletException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
#Override
public void onCancelled(DatabaseError arg0) {
}
};
//Set up database reference to notify node here
messageRef = FirebaseDatabase.getInstance().getReference().child(NOTIFY);
//Add value listener to database reference here
messageRef.addValueEventListener(lastMsgListener);
}
"Java servlet is just a personal test. Some parts have been edited or removed to only give an idea about it's setup this is in no way production ready servlet please don't just copy - paste. I encourage you to understand and build your own."

Edit: you should take a look at Firebase Cloud Functions, which let you do that without having to create a Node.js server

Android: What is transport and jsonFactory in GoogleIdTokenVerifier.Builder?

in the blow code, whats is transport and jsonFactory ? (I do not understand)
https://developers.google.com/identity/sign-in/android/backend-auth#using-a-google-api-client-library
import com.google.api.client.googleapis.auth.oauth2.GoogleIdToken;
import com.google.api.client.googleapis.auth.oauth2.GoogleIdToken.Payload;
import com.google.api.client.googleapis.auth.oauth2.GoogleIdTokenVerifier;
...
GoogleIdTokenVerifier verifier = new GoogleIdTokenVerifier.Builder(transport /**Here**/, jsonFactory /**Here**/)
.setAudience(Arrays.asList(CLIENT_ID))
// If you retrieved the token on Android using the Play Services 8.3 API or newer, set
// the issuer to "https://accounts.google.com". Otherwise, set the issuer to
// "accounts.google.com". If you need to verify tokens from multiple sources, build
// a GoogleIdTokenVerifier for each issuer and try them both.
.setIssuer("https://accounts.google.com")
.build();
// (Receive idTokenString by HTTPS POST)
GoogleIdToken idToken = verifier.verify(idTokenString);
if (idToken != null) {
Payload payload = idToken.getPayload();
// Print user identifier
String userId = payload.getSubject();
System.out.println("User ID: " + userId);
// Get profile information from payload
String email = payload.getEmail();
boolean emailVerified = Boolean.valueOf(payload.getEmailVerified());
String name = (String) payload.get("name");
String pictureUrl = (String) payload.get("picture");
String locale = (String) payload.get("locale");
String familyName = (String) payload.get("family_name");
String givenName = (String) payload.get("given_name");
// Use or store profile information
// ...
} else {
System.out.println("Invalid ID token.");
}

Since all the other answers are blah blah blah, here's a short answer:
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.gson.GsonFactory;
GoogleIdTokenVerifier verifier =
new GoogleIdTokenVerifier.Builder(new NetHttpTransport(), new GsonFactory());

The GoogleIdTokenVerifier.Builder returns a GoogleIdTokenVerifier that will make a request to the tokeninfo endpoint with the transport you give it and use the JSONFactory to create a parser to parse the response.
Here is an example of an authenticator for a Cloud Endpoints project that uses the GoogleIdTokenVerifier.Builder
public class GoogleAuthenticator implements Authenticator {
private static final Logger log = Logger.getLogger(GoogleAuthenticator.class.getName());
private static final JacksonFactory jacksonFactory = new JacksonFactory();
// From: https://developers.google.com/identity/sign-in/android/backend-auth#using-a-google-api-client-library
// If you retrieved the token on Android using the Play Services 8.3 API or newer, set
// the issuer to "https://accounts.google.com". Otherwise, set the issuer to
// "accounts.google.com". If you need to verify tokens from multiple sources, build
// a GoogleIdTokenVerifier for each issuer and try them both.
GoogleIdTokenVerifier verifierForNewAndroidClients = new GoogleIdTokenVerifier.Builder(UrlFetchTransport.getDefaultInstance(), jacksonFactory)
.setAudience(Arrays.asList(CRLConstants.IOS_CLIENT_ID, CRLConstants.ANDROID_CLIENT_ID_RELEASE, CRLConstants.ANDROID_CLIENT_ID_DEBUG))
.setIssuer("https://accounts.google.com")
.build();
GoogleIdTokenVerifier verifierForOtherClients = new GoogleIdTokenVerifier.Builder(UrlFetchTransport.getDefaultInstance(), jacksonFactory)
.setAudience(Arrays.asList(CRLConstants.IOS_CLIENT_ID, CRLConstants.ANDROID_CLIENT_ID_RELEASE, CRLConstants.ANDROID_CLIENT_ID_DEBUG))
.setIssuer("accounts.google.com")
.build();
// Custom Authenticator class for authenticating google accounts
#Override
public User authenticate(HttpServletRequest request) {
String token = request.getHeader("google_id_token");
if (token != null) {
GoogleIdToken idToken = null;
try {
idToken = verifierForNewAndroidClients.verify(token);
if(idToken == null) idToken = verifierForOtherClients.verify(token);
if (idToken != null) {
GoogleIdToken.Payload payload = idToken.getPayload();
// Get profile information from payload
String userId = payload.getSubject();
String email = payload.getEmail();
return new GoogleUser(userId, email);
} else {
log.warning("Invalid Google ID token.");
}
} catch (GeneralSecurityException e) {
log.warning(e.getLocalizedMessage());
} catch (IOException e) {
log.warning(e.getLocalizedMessage());
}
}
return null;
}
}

You need to select transport according to the platform on which you are running the code.
Quoting from the documentation
Implementation is thread-safe, and sub-classes must be thread-safe. For maximum efficiency, applications should use a single globally-shared instance of the HTTP transport.
The recommended concrete implementation HTTP transport library to use depends on what environment you are running in:
Google App Engine: use com.google.api.client.extensions.appengine.http.UrlFetchTransport.
com.google.api.client.apache.ApacheHttpTransport doesn't work on App Engine because the Apache HTTP Client opens its own sockets (though in theory there are ways to hack it to work on App Engine that might work).
com.google.api.client.javanet.NetHttpTransport is discouraged due to a bug in the App Engine SDK itself in how it parses HTTP headers in the response.
Android:
For maximum backwards compatibility with older SDK's use newCompatibleTransport from com.google.api.client.extensions.android.http.AndroidHttp (read its JavaDoc for details).
If your application is targeting Gingerbread (SDK 2.3) or higher, simply use com.google.api.client.javanet.NetHttpTransport.
Other Java environments
com.google.api.client.javanet.NetHttpTransport is based on the HttpURLConnection built into the Java SDK, so it is normally the preferred choice.
com.google.api.client.apache.ApacheHttpTransport is a good choice for users of the Apache HTTP Client, especially if you need some of the configuration options available in that library.
Documentation Link: https://developers.google.com/api-client-library/java/google-http-java-client/reference/1.19.0/com/google/api/client/http/HttpTransport?is-external=true
If you blindly follow the 2nd answer to the question, you will get the exception Caused by: java.lang.ClassNotFoundException: com.google.appengine.api.urlfetch.HTTPMethod

JacksonFactory is deprecated. So this works.
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.gson.GsonFactory;
GoogleIdTokenVerifier verifier = new GoogleIdTokenVerifier.Builder(new NetHttpTransport(), new GsonFactory())
.setAudience(Arrays.asList(CRLConstants.IOS_CLIENT_ID, CRLConstants.ANDROID_CLIENT_ID_RELEASE, CRLConstants.ANDROID_CLIENT_ID_DEBUG))
.setIssuer("accounts.google.com")
.build();

how to connect apigee proxy (Oauth verify) by using apigee android sdk?

i would like to use apigee android sdk in android app. By using android sdk, I would like to connect apigee end point proxy but api proxy has got Oauth 2.0 verification. How to access our proxy?
//Create client entity
String ORGNAME = "your-org";
String APPNAME = "your-app";
ApigeeClient apigeeClient = new ApigeeClient(ORGNAME,APPNAME);
DataClient dataClient = apigeeClient.getDataClient();
String type = "item"; //entity type to be retrieved
Map queryString = null; //we don't need any additional query parameters, in this case
//call getCollectionAsync to initiate the asynchronous API call
dataClient.getCollectionAsync(type, queryString, new ApiResponseCallback() {
//If getEntitiesAsync fails, catch the error
#Override
public void onException(Exception e) {
// Error
}
//If getCollectionAsync is successful, handle the response object
#Override
public void onResponse(ApiResponse response) {
try {
if (response != null) {
// Success
}
} catch (Exception e) { //The API request returned an error
// Fail
}
}
});

There is currently no support for OAuth in the Android SDK.

GCM Service for android shows java.net.UnknownHostException: android.googleapis.com

Code for the GCMService:
package com.avilyne.gcm;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.google.android.gcm.server.Message;
import com.google.android.gcm.server.MulticastResult;
import com.google.android.gcm.server.Sender;
/**
* Servlet implementation class GCMBroadcast
*/
#WebServlet("/GCMBroadcast")
public class GCMBroadcast extends HttpServlet {
private static final long serialVersionUID = 1L;
// The SENDER_ID here is the "Browser Key" that was generated when I
// created the API keys for my Google APIs project.
private static final String SENDER_ID = "AIzaSyCOLAYwS2P3ELqnTiPs3VPHGquQy1UoEIQ";
// This is a *cheat* It is a hard-coded registration ID from an Android device
// that registered itself with GCM using the same project id shown above.
private static final String ANDROID_DEVICE = "APA91bEF-_Y7t3Vc59OGuK9gnBWDegE4g2KyVgNeVIZbjGWe-4b9FMHrL82oOEYRPVz7_GaCOHbq3PatsuU_pk8jhvGng3Xp-CAv48iPqamer8Y2aajyTvUho9hsy39uNudA8XI4ML09eUsPNH87zcuGc_v2uJj65g";
// This array will hold all the registration ids used to broadcast a message.
// for this demo, it will only have the ANDROID_DEVICE id that was captured
// when we ran the Android client app through Eclipse.
private List<String> androidTargets = new ArrayList<String>();
/**
* #see HttpServlet#HttpServlet()
*/
public GCMBroadcast() {
super();
// we'll only add the hard-coded *cheat* target device registration id
// for this demo.
androidTargets.add(ANDROID_DEVICE);
}
// This doPost() method is called from the form in our index.jsp file.
// It will broadcast the passed "Message" value.
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// We'll collect the "CollapseKey" and "Message" values from our JSP page
String collapseKey = "";
String userMessage = "";
try {
userMessage = request.getParameter("Message");
collapseKey = request.getParameter("CollapseKey");
} catch (Exception e) {
e.printStackTrace();
return;
}
// Instance of com.android.gcm.server.Sender, that does the
// transmission of a Message to the Google Cloud Messaging service.
Sender sender = new Sender(SENDER_ID);
// This Message object will hold the data that is being transmitted
// to the Android client devices. For this demo, it is a simple text
// string, but could certainly be a JSON object.
Message message = new Message.Builder()
// If multiple messages are sent using the same .collapseKey()
// the android target device, if it was offline during earlier message
// transmissions, will only receive the latest message for that key when
// it goes back on-line.
.collapseKey(collapseKey)
.timeToLive(30)
.delayWhileIdle(true)
.addData("message", userMessage)
.build();
try {
// use this for multicast messages. The second parameter
// of sender.send() will need to be an array of register ids.
MulticastResult result = sender.send(message, androidTargets, 1);
if (result.getResults() != null) {
int canonicalRegId = result.getCanonicalIds();
if (canonicalRegId != 0) {
}
} else {
int error = result.getFailure();
System.out.println("Broadcast failure: " + error);
}
} catch (Exception e) {
e.printStackTrace();
}
// We'll pass the CollapseKey and Message values back to index.jsp, only so
// we can display it in our form again.
request.setAttribute("CollapseKey", collapseKey);
request.setAttribute("Message", userMessage);
request.getRequestDispatcher("index.jsp").forward(request, response);
}
}
Since it is a web service, it does not have android_manifest.xml. So permission for internet cannot be added.
If I want to change the host(android.googleapis.com), then how should I do it. (it seems broken).

Have you tried to turn off your firewall? You have to enable gcm ports.
If your organization has a firewall that restricts the traffic to or
from the Internet, you need to configure it to allow connectivity with
GCM. The ports to open are: 5228, 5229, and 5230. GCM typically only
uses 5228, but it sometimes uses 5229 and 5230. GCM doesn't provide
specific IPs, so you should allow your server to accept incoming
connections from all IP addresses contained in the IP blocks listed in
Google's ASN of 15169.
BTW GCM message request is a simple http post, without Message Builder you have to post a message in json format.
Android developer site
More information about message fields

How to create server for GCM project in Android

I am creating a project on Google Cloud Messaging (GCM) and am following this tutorial.
I am done with the client-side work and set up the device on the client side. Also I had registered the device using the following code.
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
GCMRegistrar.checkDevice(this);
GCMRegistrar.checkManifest(this);
final String regId = GCMRegistrar.getRegistrationId(this);
if (regId.equals("")) {
GCMRegistrar.register(this, "483910217912");
Log.d(tag, "Registered");
}
else {
Log.v(tag, "Already registered");
}
}
Now I am stuck at a point to create server for my GCM project. Note that I am creating a project to notify when a new message is received. However, I had not implemented the service to receive a message, but I will implement it when the server setting is finished.

You can create a GCM server in Android using the blog post Google cloud Messaging (GCM) tutorial , but I would prefer to use PHP for server side code. You can create a GCM Server in cURL (PHP) in easy steps:
Create a server key from the Google API console page.
Identify the device token of a device for which this message is sent to.
You can find the easy steps in How to implement a GCM PHP push server for Android to implement the push server.

you can use this code
package yourpackage.android.gcm.server;
import com.google.android.gcm.server.Message;
import com.google.android.gcm.server.MulticastResult;
import com.google.android.gcm.server.Sender;
import java.util.ArrayList;
class Notify {
public static void main(String args[]) {
try {
Sender sender = new Sender("AIzaSyCn3N2OIm-EDtiGwTyQfSIB8NRvDtIOx30");
ArrayList<String> devicesList = new ArrayList<String>();
//add you deviceID
devicesList.add("APA91bELVJbxB_NLnLbTkkkX87SDdkJc6OfCN2slhC9t4cLq-KA32eGgiW4-Gi--ZEsEMKIh0AtYJMs5rQGswfm3cH1qK853WcpV98bkaplAaC5AiycDmifuVFSRl21vgf-Rqj0dCrFF");
//devicesList.add("APA91bHIdM4XGqrjJLTuwCX5OOrTYG4ACXYEVkZDM1bPs5qFdzJP4Bpql-sZqyKB8BU7fDtdxB84aTygHLyASYg_XNY6lqrcA4wj4sZHJXGVFzz_0UEADMfFCx9NAfRZxunIYso_dkBa");
//APA91bFA-i2l3iEMnIBs0JK80pTLHOsE7p1s-DysRpKGas1MQOVILyIs9xwY7soysSWGz5Uif68uXR6F5Xn0tCTYesv78uQZxhC310a1cvf8aFohhfMGY6awbOSg3t1GRz2i3U-8kVSF
// Use this line to send message without payload data
// Message message = new Message.Builder().build();
// use this line to send message with payload data
Message message = new Message.Builder()
//.collapseKey("message")
//.timeToLive(241000)
.delayWhileIdle(true)
.addData("message", "Your message send")
.build();
/**/
// Use this code to send to a single device
// Result result = sender
// .send(message,
// "APA91bGiRaramjyohc2lKjAgFGpzBwtEmI8tJC30O89C2b3IjP1CuMeU1h9LMjKhmWuZwcXZjy1eqC4cE0tWBNt61Kx_SuMF6awzIt8WNq_4AfwflaVPHQ0wYHG_UX3snjp_U-5kJkmysdRlN6T8xChB1n3DtIq98w",
// 1);
// Use this for multicast messages
MulticastResult result = sender.send(message, devicesList, 1);
//sender.send(message, devicesList, 0);
System.out.println(result.toString());
if (result.getResults() != null) {
int canonicalRegId = result.getCanonicalIds();
if (canonicalRegId != 0) {
}
} else {
int error = result.getFailure();
System.out.println(error);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}

The com.google.android.gcm.server library is deprecated. Just encode your message to JSON object and POST it to GCM URL https://android.googleapis.com/gcm/send
JSON example:
{
"registration_ids" : ["APA91bHun4MxP5egoKMwt2KZFBaFUH-1RYqx...",...],
"data" : {
"Team" : "Portugal",
"Score" : "3",
"Player" : "Varela",
},
}
Here is more http://developer.android.com/google/gcm/http.html

You can find sample code for gcm-client and gcm-server in the Android SDK directory. It is good point to get started. Directory is :
path_to_android_sdk/extras/google/gcm/samples

In your main function implement following code to send push notification to your app
final String apiKey = "specify your api key generated by gcm";
To make http connection to gcm using following code
URL url = new URL("https://android.googleapis.com/g...");
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setDoOutput(true);
conn.setRequestMethod("POST");
conn.setRequestProperty("Content-Type", "application/json");
conn.setRequestProperty("Authorization", "key="+apiKey);
conn.setDoOutput(true);
JSON message format accepted by GCM
String input = "{\"registration_ids\" : [\"Specify token you got from GCM\"],\"data\" : {\"message\": \"hai welcome\"},}";
To send notification
OutputStream os = conn.getOutputStream();
os.write(input.getBytes());
os.flush();
In your client app you need to have proper BroadcastReceiver class to receive the message sent from GCM

I would insist you to test the demo that is being provided on the develpers site. I had just created a demo sample based on that with all the steps that one should follow for executing the demo sample. You can check my blog and also find the source from my github.