I saw recently that Sponge API still uses the old Date API.
If Sponge support Java 8, I think Sponge should not support the oldest API of JDK 1.0!
Almost every methods are deprecated, look Date (Java Platform SE 7 ).
There is a new date and time API !
Use LocalDateTime or another amazing classes of Java 8.
Yes we are aware, please create an issue at Issues · SpongePowered/SpongeAPI · GitHub
We will update to newer Date API soon =).