FCM XMPP java server app - google-app-engine

Question

I want to deploy a FCM XMPP app on Google AppEngine. I'm using this library https://github.com/thelong1EU/fcmxmppserver but I'm new on this backend side so I need some help. I managed to deploy it but it doesn't run. I don't know how to make the AppEngine call the main funtion here:
public class EntryPoint {
public static void main(String[] args) {
final String fcmProjectSenderId = senderID;
final String fcmServerKey = key;
CcsClient ccsClient = CcsClient.prepareClient(fcmProjectSenderId, fcmServerKey, false);
try {
ccsClient.connect();
} catch (XMPPException e) {
e.printStackTrace();
}
}
}
If i run just this function it all works well, but when deployed it doesn't start. What am I missing?

Answer 1

So I found out reading this:
https://cloud.google.com/appengine/docs/standard/java/an-overview-of-app-engine#scaling_types_and_instance_classes
When the app load it does a GET to /_ah/stop so I needed to add this to my servlet mapping. I did it like this:
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee">
<servlet>
<servlet-name>Start</servlet-name>
<servlet-class>eu.long1.jwnotes.fcmserver.StartServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Start</servlet-name>
<url-pattern>/_ah/start</url-pattern>
<url-pattern>/_ah/stop</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
</welcome-file-list>
</web-app>
And the in the doGet() I do this:
public class StartServlet extends HttpServlet {
private static final String GET_START = "/_ah/start";
private static final String GET_STOP = "/_ah/stop";
#Override
public void init() throws ServletException {
//init the servlet
}
#Override
public void doGet(HttpServletRequest req, HttpServletResponse resp)
throws IOException {
switch (req.getRequestURI()) {
case GET_START:
//do something
resp.setStatus(SC_OK);
break;
case GET_STOP:
//do something else
break;
}
}
}
I don't know if this is the recommended way but it works for now. If I find something else I will post.