<?php
    // Replace with the real server API key from Google APIs
    $apiKey = "your api key";

    // Replace with the real client registration IDs
    $registrationIDs = array( "reg id1","reg id2");

    // Message to be sent
    $message = "hi Shailesh";

    // Set POST variables
    $url = 'https://android.googleapis.com/gcm/send';

    $fields = array(
        'registration_ids' => $registrationIDs,
        'data' => array( "message" => $message ),
    );
    $headers = array(
        'Authorization: key=' . $apiKey,
        'Content-Type: application/json'
    );

    // Open connection
    $ch = curl_init();

    // Set the URL, number of POST vars, POST data
    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_POSTFIELDS, json_encode( $fields));

    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    // curl_setopt($ch, CURLOPT_POST, true);
    // curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode( $fields));

    // Execute post
    $result = curl_exec($ch);

    // Close connection
    curl_close($ch);
    echo $result;
    //print_r($result);
    //var_dump($result);
?>

使用这个

 function pnstest(){

                $data = array('post_id'=>'12345','title'=>'A Blog post', 'message' =>'test msg');

                $url = 'https://fcm.googleapis.com/fcm/send';

                $server_key = 'AIzaSyDVpDdS7EyNgMUpoZV6sI2p-cG';

                $target ='fO3JGJw4CXI:APA91bFKvHv8wzZ05w2JQSor6D8lFvEGE_jHZGDAKzFmKWc73LABnumtRosWuJx--I4SoyF1XQ4w01P77MKft33grAPhA8g-wuBPZTgmgttaC9U4S3uCHjdDn5c3YHAnBF3H';

                $fields = array();
                $fields['data'] = $data;
                if(is_array($target)){
                    $fields['registration_ids'] = $target;
                }else{
                    $fields['to'] = $target;
                }

                //header with content_type api key
                $headers = array(
                    'Content-Type:application/json',
                  'Authorization:key='.$server_key
                );

                $ch = curl_init();
                curl_setopt($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 ($result === FALSE) {
                    die('FCM Send Error: ' . curl_error($ch));
                }
                curl_close($ch);
                return $result;

}

这段代码将通过PHP CURL向多个注册id发送一个GCM消息。

// Payload data you want to send to Android device(s)
// (it will be accessible via intent extras)    
$data = array('message' => 'Hello World!');

// The recipient registration tokens for this notification
// https://developer.android.com/google/gcm/    
$ids = array('abc', 'def');

// Send push notification via Google Cloud Messaging
sendPushNotification($data, $ids);

function sendPushNotification($data, $ids) {
    // Insert real GCM API key from the Google APIs Console
    // https://code.google.com/apis/console/        
    $apiKey = 'abc';

    // Set POST request body
    $post = array(
                    'registration_ids'  => $ids,
                    'data'              => $data,
                 );

    // Set CURL request headers 
    $headers = array( 
                        'Authorization: key=' . $apiKey,
                        'Content-Type: application/json'
                    );

    // Initialize curl handle       
    $ch = curl_init();

    // Set URL to GCM push endpoint     
    curl_setopt($ch, CURLOPT_URL, 'https://gcm-http.googleapis.com/gcm/send');

    // Set request method to POST       
    curl_setopt($ch, CURLOPT_POST, true);

    // Set custom request headers       
    curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

    // Get the response back as string instead of printing it       
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

    // Set JSON post data
    curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($post));

    // Actually send the request    
    $result = curl_exec($ch);

    // Handle errors
    if (curl_errno($ch)) {
        echo 'GCM error: ' . curl_error($ch);
    }

    // Close curl handle
    curl_close($ch);

    // Debug GCM response       
    echo $result;
}

许多教程都过时了，甚至当前的代码都没有考虑设备注册id何时更新或设备取消注册。如果不检查这些项目，最终将导致无法接收消息的问题。http://forum.loungekatt.com/viewtopic.php?t=63#p181

下面是@Elad Nava发布的上述PHP代码的android代码

java(启动程序活动)

public class MainActivity extends AppCompatActivity {
    String PROJECT_NUMBER="your project number/sender id";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);



        GCMClientManager pushClientManager = new GCMClientManager(this, PROJECT_NUMBER);
        pushClientManager.registerIfNeeded(new GCMClientManager.RegistrationCompletedHandler() {
            @Override
            public void onSuccess(String registrationId, boolean isNewRegistration) {

                Log.d("Registration id", registrationId);
                //send this registrationId to your server
            }

            @Override
            public void onFailure(String ex) {
                super.onFailure(ex);
            }
        });
    }
}

GCMClientManager.java

public class GCMClientManager {
    // Constants
    public static final String TAG = "GCMClientManager";
    public static final String EXTRA_MESSAGE = "message";
    public static final String PROPERTY_REG_ID = "your sender id";
    private static final String PROPERTY_APP_VERSION = "appVersion";
    private final static int PLAY_SERVICES_RESOLUTION_REQUEST = 9000;
    // Member variables
    private GoogleCloudMessaging gcm;
    private String regid;
    private String projectNumber;
    private Activity activity;
    public GCMClientManager(Activity activity, String projectNumber) {
        this.activity = activity;
        this.projectNumber = projectNumber;
        this.gcm = GoogleCloudMessaging.getInstance(activity);
    }
    /**
     * @return Application's version code from the {@code PackageManager}.
     */
    private static int getAppVersion(Context context) {
        try {
            PackageInfo packageInfo = context.getPackageManager()
                    .getPackageInfo(context.getPackageName(), 0);
            return packageInfo.versionCode;
        } catch (NameNotFoundException e) {
            // should never happen
            throw new RuntimeException("Could not get package name: " + e);
        }
    }
    // Register if needed or fetch from local store
    public void registerIfNeeded(final RegistrationCompletedHandler handler) {
        if (checkPlayServices()) {
            regid = getRegistrationId(getContext());
            if (regid.isEmpty()) {
                registerInBackground(handler);
            } else { // got id from cache
                Log.i(TAG, regid);
                handler.onSuccess(regid, false);
            }
        } else { // no play services
            Log.i(TAG, "No valid Google Play Services APK found.");
        }
    }
    /**
     * Registers the application with GCM servers asynchronously.
     * <p>
     * Stores the registration ID and app versionCode in the application's
     * shared preferences.
     */
    private void registerInBackground(final RegistrationCompletedHandler handler) {
        new AsyncTask<Void, Void, String>() {
            @Override
            protected String doInBackground(Void... params) {
                try {
                    if (gcm == null) {
                        gcm = GoogleCloudMessaging.getInstance(getContext());
                    }
                    InstanceID instanceID = InstanceID.getInstance(getContext());
                    regid = instanceID.getToken(projectNumber, GoogleCloudMessaging.INSTANCE_ID_SCOPE, null);
                    Log.i(TAG, regid);
                    // Persist the regID - no need to register again.
                    storeRegistrationId(getContext(), regid);
                } catch (IOException ex) {
                    // If there is an error, don't just keep trying to register.
                    // Require the user to click a button again, or perform
                    // exponential back-off.
                    handler.onFailure("Error :" + ex.getMessage());
                }
                return regid;
            }
            @Override
            protected void onPostExecute(String regId) {
                if (regId != null) {
                    handler.onSuccess(regId, true);
                }
            }
        }.execute(null, null, null);
    }
    /**
     * Gets the current registration ID for application on GCM service.
     * <p>
     * If result is empty, the app needs to register.
     *
     * @return registration ID, or empty string if there is no existing
     *     registration ID.
     */
    private String getRegistrationId(Context context) {
        final SharedPreferences prefs = getGCMPreferences(context);
        String registrationId = prefs.getString(PROPERTY_REG_ID, "");
        if (registrationId.isEmpty()) {
            Log.i(TAG, "Registration not found.");
            return "";
        }
        // Check if app was updated; if so, it must clear the registration ID
        // since the existing regID is not guaranteed to work with the new
        // app version.
        int registeredVersion = prefs.getInt(PROPERTY_APP_VERSION, Integer.MIN_VALUE);
        int currentVersion = getAppVersion(context);
        if (registeredVersion != currentVersion) {
            Log.i(TAG, "App version changed.");
            return "";
        }
        return registrationId;
    }
    /**
     * Stores the registration ID and app versionCode in the application's
     * {@code SharedPreferences}.
     *
     * @param context application's context.
     * @param regId registration ID
     */
    private void storeRegistrationId(Context context, String regId) {
        final SharedPreferences prefs = getGCMPreferences(context);
        int appVersion = getAppVersion(context);
        Log.i(TAG, "Saving regId on app version " + appVersion);
        SharedPreferences.Editor editor = prefs.edit();
        editor.putString(PROPERTY_REG_ID, regId);
        editor.putInt(PROPERTY_APP_VERSION, appVersion);
        editor.commit();
    }
    private SharedPreferences getGCMPreferences(Context context) {
        // This sample app persists the registration ID in shared preferences, but
        // how you store the regID in your app is up to you.
        return getContext().getSharedPreferences(context.getPackageName(),
                Context.MODE_PRIVATE);
    }
    /**
     * Check the device to make sure it has the Google Play Services APK. If
     * it doesn't, display a dialog that allows users to download the APK from
     * the Google Play Store or enable it in the device's system settings.
     */
    private boolean checkPlayServices() {
        int resultCode = GooglePlayServicesUtil.isGooglePlayServicesAvailable(getContext());
        if (resultCode != ConnectionResult.SUCCESS) {
            if (GooglePlayServicesUtil.isUserRecoverableError(resultCode)) {
                GooglePlayServicesUtil.getErrorDialog(resultCode, getActivity(),
                        PLAY_SERVICES_RESOLUTION_REQUEST).show();
            } else {
                Log.i(TAG, "This device is not supported.");
            }
            return false;
        }
        return true;
    }
    private Context getContext() {
        return activity;
    }
    private Activity getActivity() {
        return activity;
    }
    public static abstract class RegistrationCompletedHandler {
        public abstract void onSuccess(String registrationId, boolean isNewRegistration);
        public void onFailure(String ex) {
            // If there is an error, don't just keep trying to register.
            // Require the user to click a button again, or perform
            // exponential back-off.
            Log.e(TAG, ex);
        }
    }
}

java(通知生成器)

public class PushNotificationService extends GcmListenerService{

    public static int MESSAGE_NOTIFICATION_ID = 100;

    @Override
    public void onMessageReceived(String from, Bundle data) {
        String message = data.getString("message");
        sendNotification("Hi-"+message, "My App sent you a message");
    }

    private void sendNotification(String title, String body) {
        Context context = getBaseContext();
        NotificationCompat.Builder mBuilder = (NotificationCompat.Builder) new NotificationCompat.Builder(context)
                .setSmallIcon(R.mipmap.ic_launcher).setContentTitle(title)
                .setContentText(body);
        NotificationManager mNotificationManager = (NotificationManager) context
                .getSystemService(Context.NOTIFICATION_SERVICE);
        mNotificationManager.notify(MESSAGE_NOTIFICATION_ID, mBuilder.build());
    }
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />
<permission android:name="com.example.gcm.permission.C2D_MESSAGE"
    android:protectionLevel="signature" />
<uses-permission android:name="com.example.gcm.permission.C2D_MESSAGE" />
<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme" >
    <activity android:name=".MainActivity" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

    <service
        android:name=".PushNotificationService"
        android:exported="false">
        <intent-filter>
            <action android:name="com.google.android.c2dm.intent.RECEIVE" />
        </intent-filter>
    </service>

    <receiver
        android:name="com.google.android.gms.gcm.GcmReceiver"
        android:exported="true"
        android:permission="com.google.android.c2dm.permission.SEND">
        <intent-filter>
            <action android:name="com.google.android.c2dm.intent.RECEIVE" />
            <category android:name="package.gcmdemo" />
        </intent-filter>
    </receiver>
</application>

你可以在packagist上使用这个PHP库:

https://github.com/CoreProc/gcm-php

安装后，你可以这样做:

$gcmClient = new GcmClient('your-gcm-api-key-here');

$message = new Message($gcmClient);

$message->addRegistrationId('xxxxxxxxxx');
$message->setData([
    'title' => 'Sample Push Notification',
    'message' => 'This is a test push notification using Google Cloud Messaging'
]);

try {

    $response = $message->send();

    // The send() method returns a Response object
    print_r($response);

} catch (Exception $exception) {

    echo 'uh-oh: ' . $exception->getMessage();

}