The following program won't work on Tomcat's WebSocket client jars, both 8.0.20 and Trunk:

public class App2 {
    @ClientEndpoint
    public static class Client {
        @OnOpen
        public void onOpen(Session s) throws Exception {
            System.out.println("Sending PING");
            s.getBasicRemote().sendText("PING");
        }

        @OnMessage
        public void onMessage(Session s, String msg) throws Exception {
            System.out.println("GOT: " + msg);
            Thread.sleep(1000);
            s.getBasicRemote().sendText("PING");
            System.out.println("Sending PING");
        }
    }

    public static void main(final String[] args) throws Exception {
        ContainerProvider.getWebSocketContainer().connectToServer(
                Client.class,
                URI.create("ws://echo.websocket.org"));
        Thread.sleep(Long.MAX_VALUE);
    }
}

It fails with:

Exception in thread "main" javax.websocket.DeploymentException: The
HTTP request to initiate the WebSocket connection failed
    at org.apache.tomcat.websocket.WsWebSocketContainer.connectToServer(WsWebSocketContainer.java:357)
    at org.apache.tomcat.websocket.WsWebSocketContainer.connectToServer(WsWebSocketContainer.java:164)
    at org.apache.tomcat.websocket.WsWebSocketContainer.connectToServer(WsWebSocketContainer.java:181)
    at io.davinci.test_sync_gateway_websocket.App2.main(App2.java:31)
Caused by: java.io.EOFException
    at org.apache.tomcat.websocket.WsWebSocketContainer.processResponse(WsWebSocketContainer.java:606)
    at org.apache.tomcat.websocket.WsWebSocketContainer.connectToServer(WsWebSocketContainer.java:309)
    ... 3 more


If you add a slash to the end of the URL, however, it connects.