If your android app needs to send messages to server only, you could use simple REST API. If you need server to the application messaging too, then you could try Cloud Messaging or just use simple WebSockets, which can give you real time performance. In the latter case you need Java implementation of WebSockets client, for instance, this one.
Realtime communication between the server and browser can be done using WebSockets too. You can use one of numerous PHP WebSockets implementation like this. Using Socket.IO could be a bit tricky, check this link to get more information.
In browser you can use standard WebSockets API. If you have requirements to support old browsers, which have no WebSockets support, then you need to check Socket.IO or SockJS library because they provide fallback mechanism.