Starting with 2.54, Jenkins now requires Java 8
We announced in January that Jenkins would be upgrading its Java runtime dependency to Java 8 this year. After a sizable amount of preparation, this week’s release of Jenkins 2.54 is the first weekly release to require a Java 8 runtime.
For users of the weekly release, this means that Jenkins 2.54 must have a Java 8 runtime installed on the system in order to run. Those using the jenkinsci/jenkins:latest Docker container won’t need to take any action, as the Java runtime environment is already bundled in the container.
In addition to upgrading the Java Runtime Environment for the controller, any connected agents must upgrade to a Java 8 runtime environment.
The Long-Term Support (LTS) release line however, has not yet been updated to require Java 8. We are expecting the first LTS release to require Java 8 in June.
Using the Maven project type with Java 7
Users with jobs configured with the "Maven project" type may not be able to use Java 7 for their Maven jobs. The correct behavior is not guaranteed so proceed at your own risk. The Maven Project uses Jenkins Remoting to establish "interceptors" within the Maven executable. Because of this, Maven uses Remoting and other Jenkins core classes, and this behavior may break an update.
See also: JENKINS-40990.
Java 9 compatibility
At this point, Jenkins does not yet support Java 9 development releases.