Streaming websockets's message with WebSocketStreamingProtocol - Atmosphere/atmosphere Wiki

By default, Atmosphere's WebSocket implementation will buffer websocket message of size up to 2 Mb. If your application is planning to send messages of larger size, it is recommended to stream those bytes instead of letting Atmosphere to read them in memory. The first task is to add, in web.xml

<init-param>
   <param-name>org.atmosphere.websocket.WebSocketProtocol</param-name>
   <param-value>org.atmosphere.websocket.protocol.StreamingHttpProtocol</param-value>
</init-param>

Note that this Protocol is only available with Atmosphere 2.1. If you are using a lower version, just write your own Protocol by copying this class.

Next, instead of writing a WebSocketHandler, write an WebSocketProtocolStream so you can manipulate the stream directly, without any buffering from Atmosphere.