is it possible to send a data when a websocket connection is opened

I am implementing a Jetty Websocket servlet. When the server receives a new connection, I want to send a message that will be read by websocket's onopen function. I want this message to be sent only during the open and not using the regular connection.SendMessage() function. Is it possible to do that? and how?

Solution

There is no support for this in the protocol but you could fudge something yourself.

When your server completes a handshake, store the initial message you want to deliver to a client.
In your client's onopen function, send a "read initial message" request.
In your server, check that this client hasn't read its initial message; respond with the message; set a flag saying that the initial message has been sent.
Your client and server are both now free to send other messages.