Ask HN: Languages/tech for my website

Hi. I am building a dynamic website with a lot of server push data and connected user interactions.

The server side engine (contains the business Model) will be a standalone Java app, that accesses MySQL DB and communicates with the webserver app in some form of messaging or socket.

The client/browser side I prefer Javascript.

Now what tech and lang do you recommend to bridge the client and the business engine? This will include the webserver and the webapp that will also accesses the same MySQL.

The requirements are: it needs to be fast, able to handle lot of push/pull data traffic in real time to many users, and secure (encryption?). The technology should be well supported on a production level and not a dead end, with consideration for expanding to mobile apps. Any suggestions?