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InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
In the ancient times (12y ago) I managed to build a reasonably complicated 10+ GUI view / 1k+ user WebApp using Java only. I used GWT[1] and Sencha's Ext-GWT, now called GXT[2]
Depending on your needs, in 2021 I don't recommend starting with these. The reason I used it was that you could actually create widget-based SPAs using Java only (no JS, no CSS, no HTML), had excellent debugging support, and prototyping was fast.
But the webapp was more functional than pleasing in appearance. For an intranet tool / configuration utility etc. I might consider it again, but anything else where you want attract possible new users... I think you have to learn modern web dev stacks.
[1]: http://www.gwtproject.org/
[2]: https://www.sencha.com/products/gxt/