How to close java-ee websocket connection properly

Question

I am implementing a small chat application using java-ee websockets.
At one time I want to close session for a client for various reasons so for closing connection.
For closing connection I called onClose function and in that function I called session.close() But after that I got the following error:

java.lang.IllegalStateException: The WebSocket session has been closed and no method (apart from close()) may be called on a closed session
    at org.apache.tomcat.websocket.WsSession.checkState(WsSession.java:643)
    at org.apache.tomcat.websocket.WsSession.addMessageHandler(WsSession.java:168)
    at org.apache.tomcat.websocket.pojo.PojoEndpointBase.doOnOpen(PojoEndpointBase.java:81)
    at org.apache.tomcat.websocket.pojo.PojoEndpointServer.onOpen(PojoEndpointServer.java:70)
    at org.apache.tomcat.websocket.server.WsHttpUpgradeHandler.init(WsHttpUpgradeHandler.java:129)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:629)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)

I'm not sure what I did wrong and I why I got this exception.

Answer 1

I was having the same issue as I started learning this stuff today.

What I have found so far is that on the server at the annotation @OnMessage I was closing the connection when the Server received a "quit" message by calling the session.close. Then at the end of the @OnMessage I was issuing the return that is mandatory as the method requires a return and it was the return that was throwing the Exception since the session has been closed already.

My solution is to instead of making the server close the session I send a message "youquit" back to the client and I have the client calling the session.close.

The server now receives the close event and is ready for the next connection and the client ends without exception.

@OnMessage
public String onMessage(String message, Session session) throws DeploymentException, IOException {
    switch (message) {
        case "quit":
            //session.close(new CloseReason(CloseCodes.NORMAL_CLOSURE, "Game ended"));
            message = "you" + message;
            break;
    }
    return message;
}

@OnClose
public void onClose(Session session, CloseReason closeReason) {
    logger.info(String.format("Session %s closed because of %s", session.getId(), closeReason));
}

I have tried to catch the exception at the return level but it does not work.

I now believe that you cannot close the connection at the @OnMessage entry point.