We have ColdFusion 2018 with Java version 10.0.1. There is also installed on the server JDK 12.0.1. Is the JDK necessary and required? We have security notice that JDK should be updated to version 15. Can this be done without causing problems for ColdFusion?
You need either the JDK or what Oracle calls the "Server JRE" - which I don't know is even available any more to be honest. These include the version of Java intended to run server applications. The regular JRE only includes the version of Java for running on your desktop. They're different in some very important ways.
You should check the ColdFusion support matrix to see what versions of Java are supported by a given version of ColdFusion. If CF 2018 supports JDK 15, you should upgrade to that. The initial version of CF 2018 supports JDK 11 according to the matrix:
So, you may need to install updates to CF 2018 before you can go beyond JDK 11, if it's supported at all. I would recommend upgrading to JDK 11 at least, if you've already installed CF 2018 update 2 installer refresh. I'd always look at the list of updates to see which if any allow you to upgrade Java, among other things.
It's pretty easy to upgrade Java for CF, if you follow the instructions and don't go beyond the supported version. This is documented in the online help somewhere, but I can't find it now. Basically, just install the latest supported version of Java somewhere, then go into the CF Administrator and change the Java path to point to the new directory, then restart CF. If you do this wrong, there will be a restore file in the CF directory that will let you go back to the old version. I'm sorry I don't have more useful information on that but I'm sure someone will chime in with specifics.
Dave Watts, Eidolon LLC
To expand on Dave's helpful answer, CF does NOT currently support Java 15 (or 14 or 13, and CF2018 supported Java 12 for a time but Oracle's support for it came and went within 6 months, so no, it's no longer supported as your folks are reporting to you.)
But Java 11 is still updated by Oracle (it's what Oracle currently "long-term suport" version of Java, along with Java 8), and it's likely that Java 17 will be the next long-LTS version. (And Adobe may not bother to offer support for a newer Java verison until then, since technically CF does not require any verison beyond 11 for now.) So until then, you should update CF2018 to the latest Java 11, which is 11.0.9 as we write.
And I have a blog post where I offer a table of each CF version (of the past 10 years) and the Java version(s) that Adobe supported for that: