Hi.
The OpenJDK JRE and Oracle JRE are mostly compatible, we were running Automic 12.0 on OpenJDK for quite some time and that worked, even through being unsupported. In principle, it really should be a drop-in replacement. Install OpenJDK, point all your Java calls (Java agents in the service manager's .smc file) to the new java.exe by means of absolute paths in that file or by systems search path, and that's that.
However, OpenJDK isn't supported with anything below 12.2. But then, V9 is out of support as a whole (and so is 10.x and soon 11.2), the current release is 12.3.
Best,
Carsten