Java WebSocket: Multi Text/Data MessageHandler

Question

Hello guys. In my WebSocket application, the WS server need to handle three kinds of message: DataPkg, SigPkg and WS_SigPkg. The DataPkg is binary for user data, with controller headers; the SigPkg is String for user data control between WS clients, and the WS_SigPkg is also String for such as registration to WS server and switching of DataPkg and SigPkg between different WS sessions.

So I put six encoder/decoders:

decoders = {SigDecoder.class, WS_SigDecoder.class, DataDecoder.class},
encoders = {SigEncoder.class, WS_SigEncoder.class, DataEncoder.class}

Then I got bellow error:

Caused by: javax.servlet.ServletException: Web socket server initialization failed.
    at org.glassfish.tyrus.servlet.TyrusServletFilter.init(TyrusServletFilter.java:126)
    at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:275)
    at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:131)
    ... 28 more
Caused by: javax.websocket.DeploymentException: Class org.sample.xyzserver.XyzServer. Text MessageHandler already registered.

Seems the GlashFish Server 4.1.1 cannot add two MessageHandlers for the String messages, though in the upper layer they are different and the decoders can find that.

Is here any miss-understanding or there is a easy work-around, or I have to refactor to use only one MessageHandler for string and one for binary? Thanks.

score 0 · Answer 1 · answered Jan 11 '16 at 14:54

This is by design of Session.addMessageHandler. You can only register one MessageHandler per message type (text, binary or pong). The Javadoc states:

Register to handle to incoming messages in this conversation. A maximum of one message handler per native websocket message type (text, binary, pong) may be added to each Session. I.e. a maximum of one message handler to handle incoming text messages a maximum of one message handler for handling incoming binary messages, and a maximum of one for handling incoming pong messages. For further details of which message handlers handle which of the native websocket message types please see MessageHandler.Whole and MessageHandler.Partial. Adding more than one of any one type will result in a runtime exception.

Java WebSocket: Multi Text/Data MessageHandler

1 Answers1