Jenkins supports Java 9 on Debian if you install OracleJava8 by Webupd8 and replace the binary files with java 9 files from http://jdk.java.net/9/ (or at least it did)

I do not recommend this as it gave me errors in the settings I was not able to resolve by myself. Additionally, I just tested this on a new server and it now says that the version is not supported which is the way it should be.

I went with sudo update-alternatives --config java.

Is this planned to be fixed in time for the end of Java 8 support?
See Oracle Java SE Support Roadmap: http://www.oracle.com/technetwork/java/eol-135779.html

Copying:
End of Public Updates for Oracle JDK 8
As outlined in the Oracle JDK Support Roadmap below, Oracle will not post further updates of Java SE 8 to its public download sites for commercial use after January 2019.

Christoph Obexer in the community we do not ETA and roadmap for it right now.
There are some changes happening in the background, and there is a general agreement that we should do it somehow. But the timing may differ.

If the support does not get delivered by Jan 2019, using other JDK distributions may be a temporary solution if you need a Java update. Too early to talk about it now IMHO, the Java 8 EoL date may change again.

Java 9 is EoL, so I have renamed ticket to Java 10. It does not change the scope much. Java 11, ehm, may be fun

I just wanted to add that I ran into the same problem when upgrading our jenkins server to Ubuntu 18.04. Antony Gelberg's solution `sudo update-alternatives --config java` solves it for me. For those who are interested, here is what happens after executing the command

```

There are 2 choices for the alternative java (providing /usr/bin/java).

Selection Path Priority Status
------------------------------------------------------------

• 0 /usr/lib/jvm/java-11-openjdk-amd64/bin/java 1101 auto mode
  1 /usr/lib/jvm/java-11-openjdk-amd64/bin/java 1101 manual mode
  2 /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java 1081 manual mode

```

After I switched back to java 8, and then `sudo service jenkins start` jenkins comes back to life again.

> Java 9 is EoL, so I have renamed ticket to Java 10. It does not change the scope much. Java 11, ehm, may be fun

Java 10 will also be EoL soon, in September 2018. On the other hand (Oracle's) Java 11 will be a 5-year Long Term Support version. 11 might be a better target version, instead of pursuing the current rabbit down the hole.

> Java 10 will also be EoL soon, in September 2018. On the other hand (Oracle's) Java 11 will be a 5-year Long Term Support version. 11 might be a better target version, instead of pursuing the current rabbit down the hole.

That's correct. We will definitely change the version when really start working on that seriously. Stay tuned

After some consideration I created a separate EPIC for Java 11: JENKINS-51805
If some tasks here are not feasible for Java 11, we can just close them as "Won't fix"

Just in case somebody is interested, we are going to have an online "Jenkins & Java 10" hackathon next week.
Everybody is welcome to join, see https://jenkins.io/blog/2018/06/08/jenkins-java10-hackathon/