gistfile1.java

<?php
         //## Function to send GCM push notification
         function sendMessageUsingGCM($registatoin_ids, $message) {

        //## Google cloud messaging GCM-API url

        $url = 'https://android.googleapis.com/gcm/send';
        $fields = array( 'registration_ids' => $registatoin_ids, 'data' => $message,);

        //## Update your Google Cloud Messaging API Key

        define("GOOGLE_API_KEY", "Place Google Api Key Here");      
        $headers = array('Authorization: key=' . GOOGLE_API_KEY,'Content-Type: application/json');
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_POST, true);
        curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt ($ch, CURLOPT_SSL_VERIFYHOST, 0);   
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
        curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
        $result = curl_exec($ch);               
        if ($result === FALSE) {
            die('Curl failed: ' . curl_error($ch));
        }
        curl_close($ch);
        return $result;

    }

    $id = 'device_id';//### Place Device ID here
    $gcmRegIds = array($id);
    $message    = $_REQUEST['message'];
    $message    = array("gcm_message" => $message);
    $pushStatus = sendMessageUsingGCM($gcmRegIds, $message);
    echo $pushStatus;

?>
Test Example : http://yoursite.com/gcm.php?message=hello
Installation Client
Step 1:
place 'manishkprgcmlibrary' downloaded library inside you project root directory
Step 2:
Add the followings dependencies to you build.gradle file
dependencies {
    compile project(':manishkprgcmlibrary')
    compile 'com.google.android.gms:play-services:+'
}
Step 3:
Add following permissions to your AndroidManifest.xml File
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.GET_ACCOUNTS" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<uses-permission android:name="android.permission.VIBRATE" />

<!-- Create Custom Permission 'your.package.name' replace with your project package  -->
<permission android:name="your.package.name.permission.C2D_MESSAGE" android:protectionLevel="signature" />

<!-- GCM Permissions Start here  -->

<uses-permission android:name="your.package.name.permission.C2D_MESSAGE" />
<uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
Step 4:
Add Broadcast and Service to your AndroidManifest.xml File
<!-- Register Broadcast receiver -->
    <receiver
        android:name="gcm.manishkpr.com.manishkprgcmlibrary.BroadCasts.GcmBroadcastReceiver"
        android:permission="com.google.android.c2dm.permission.SEND" >
        <intent-filter>
            <action android:name="com.google.android.c2dm.intent.RECEIVE" />
            <action android:name="com.google.android.c2dm.intent.REGISTRATION" />

            <category android:name="your.package.name" /> <!-- replace it with your package name -->

        </intent-filter>
    </receiver>
<!-- Register Service -->
    <service android:name="gcm.manishkpr.com.manishkprgcmlibrary.Services.GCMIntentService" />
Step 5:
//### For Registering your device
new GCMRegister(this, "Your Project Number",callBack).execute(); //## ForActivity 
new GCMRegister(getActivity(), "Your Project Number",callBack).execute(); //## For Fragment

//### You Can Get GCM ID By following Call Back

GCMRegisterCallBack callBack = new GCMRegisterCallBack() {
        @Override
        public void getGCMRegister(String id, boolean isRegister) {
            if(isRegister)
            Log.i("ID ",id);
        }
};
Step 6:
For Receiving Messages Add Broadcast to your Fragment or Activity
    BroadcastReceiver broadcastReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                String msg = intent.getExtras().get(AppConfig.GCM_MESSAGE).toString();
                Log.i("Message Received ",msg);
            }
    };

    @Override
    protected void onResume() {
        super.onResume();
        registerReceiver(broadcastReceiver, new IntentFilter(AppConfig.GCM_BROADCAST_ACTION));
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unregisterReceiver(broadcastReceiver);
    }
That's It
For More Information See The Example Inside This Library