As Java 9 has been released Openfire should support it at some point. Currently if i try to run Openfire 4.1.5 after deleting its internal jre folder (x64 version) and have Java 9 (64-bit) installed it still says it can't find suitable java. This might be the case of just wrong path variable, though usually Openfire was able to find system Java (when using 32-bit one). Java 9 comes only in 64-bit version.
As Java 9 has been released Openfire should support it at some point. Currently if i try to run Openfire 4.1.5 after deleting its internal jre folder (x64 version) and have Java 9 (64-bit) installed it still says it can't find suitable java. This might be the case of just wrong path variable, though usually Openfire was able to find system Java (when using 32-bit one). Java 9 comes only in 64-bit version.