appengine-web.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright 2015 Google Inc. All Rights Reserved.
  ~
  ~ 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.
  -->

<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">

    <!--
           User : put your application ID here
    -->
    <application>YOUR-APPLICATION-ID</application>
    <version>1</version>
    <!--
    Allows App Engine to send multiple requests to one instance in parallel:
    -->
    <threadsafe>true</threadsafe>

    <system-properties>
        <!-- Configure java.util.logging -->
        <property name="java.util.logging.config.file"
                  value="WEB-INF/logging.properties"/>

        <!--
            User : Before you run your application, you need a Google Cloud Messaging API key.
            To get one, follow this link, follow the directions and press "Create" at the end:
                https://console.developers.google.com/flows/enableapi?apiid=googlecloudmessaging&keyType=SERVER_SIDE&r=0.0.0.0/0
            Once you have your API key (which starts with “AIza...”), replace the "gcm.api.key" string in this file.
            -->

        <property name="gcm.api.key" value="YOUR-GCM-API-KEY"/>
    </system-properties>
</appengine-web-app>