Now I have some kind of an issue with the configuration of Vaadin itself, as I can see the following error messages in the console log:
WebSocket connection to 'ws://localhost:8080/app/PUSH?v-uiId=0&v-csrfToken=19ad1e55-5182-4668-8ae8-9923cee819dc&X-Atmosphere-tracking-id=0&X-Atmosphere-Framework=2.2.13.vaadin3-jquery&X-Atmosphere-Transport=websocket&X-Atmosphere-TrackMessageSize=true&Content-Type=application/json;%20charset=UTF-8&X-atmo-protocol=true' failed: Error during WebSocket handshake: Unexpected response code: 500 Websocket closed, reason: Connection was closed abnormally (that is, with no close frame being sent). Websocket closed, wasClean: false Websocket failed. Downgrading to Comet and resending
and then in every couple of seconds I get
vaadinPush.js?v2017_02_01_09_36:26 GET http://localhost:8080/app/PUSH?v-uiId=0&v-csrfToken=19ad1e55-5182-4668-8ae8…plication%2Fjson%3B%20charset%3DUTF-8&X-atmo-protocol=true&_=1485941974997 500 (Internal Server Error)
Could you please point me out how to fix this?
Thank you for your help: