Java EE 7 also comes with a standardized WebSockets client (part of JSR-356), which can be directly used in Java applications like Swing, JavaFX or Unit Tests to access remote WebSockets.
With a little help of Java EE 7, both sides can be implemented in < 9 mins :-):
Web Apps, SPA, PWA with vanilla Java Script (ES 6+), CSS 3 and WebStandards only. As simple as possible, but not simpler. See you at: (Progressive) Web apps, Single Page Apps and WebStandards airhacks workshops at MUC airport, Winter Edition
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