title: Push notifications from Web server to android application
body: <p>Hello to everyone who is viewing this question. I think this question might be quite abstract, but I couldn't find the correct answer by googling.</p>
  <p>I am trying to make an application like Starbucks Siren-Order.</p>
  <p>Our android applications are made in <code>Android-Java</code>, and we are also developing a web-server which is also
  written in <code>Java</code>, using <code>Spring-MVC</code>.</p>
  <p>Once a customer makes an order using this application(which is for customers), I want to make push notifications appear in <code>Store-Owner-Application</code>. I was thinking about using WebSocket, but is Firebase a great alternative for websocket in this case? I never used neither WebSocket or Firebase before.
  Just asking for some tips and advice. Thank you :)</p>