Visual Studio Code uses OmniSharp as middleware for the C# extension for instance to check code, find usages, and lookup types. The "rename symbol" works fine so far. I guess, but am not sure, they use the language server protocol [1] to communicate with OmniSharp.

A few months ago I stumbled upon a Java language server [2] which utilizes Eclipse JDT. Maybe if the Java language server supports refactoring and Vim support the language server protocol, we could have refactoring of Java code in Vim on par with Eclipse.

[1] https://github.com/Microsoft/language-server-protocol [2] https://github.com/gorkem/java-language-server