Java 9 is planned to be released on 21th of September. Next LTS version of SonarQube should support it as a runtime for server and scanners.
Elasticsearch 5.6.3 does not support Java 9 yet. As consequence SonarQube can't claim to support Java 9 too. Anyway the goal of this ticket is to provide a basic support, at best, so that most use-cases don't fail unexpectively :