MarsSeed  filed a deletion request for jdk9 :
EOL since March 2018, no extended support. Download 404 (funtoo.org), behind loginwall (Oracle).
I am submitting this deletion request for consideration. I don't think this package is needed anymore.
Arch still carries jre8-openjdk, and Oracle offers paid access to Oracle JDK 8 but not for 9.
Rationale for deletion: 1- If this package cannot be salvaged, it is essentially just spam on AUR. There are already too many legacy JRE and JDK packages here. 2- EOL since 2018, therefore insecure. No one should use it, there are alternatives for secure legacy versions.
Please consider and do as you see fit. :)
 https://aur.archlinux.org/account/MarsSeed/  https://aur.archlinux.org/pkgbase/jdk9/