When comparing lsp-java vs intellij-lsp-server, the Slant community recommends lsp-java for most people. In the question“What is the best Java development setup for Emacs?” lsp-java is ranked 1st while intellij-lsp-server is ranked 2nd.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Refactoring support
Pro Uses headless Eclipse in the backend
The backend is basically a lightweight version of headless Eclipse. This adds eclipse features like autocomplete and syntax checking to emacs.
Pro Maven/Gradle integration
Built-in integration for Maven and Gradle for project management, project imports, automatic builds, etc.
Pro Pretty fast
Compared to emacs-eclim, this feels very fast, even over ssh X11 forwarding.
Pro Almost sufficient to replace the IntelliJ frontend
You can toggle the IntelliJ GUI on or off with M-x lsp-intellij-toggle-frame-visibility which helps smooth over the parts which aren’t yet strong enough from Emacs.
Pro Uses IntelliJ backend
Cons
Con You must have IntelliJ IDEA installed to use this mode
Since the internal API directly communicates with IntelliJ IDEA, you must have it installed to use the mode.