Play Framework: Java version prior to 1.8 are not supported

Question

I have an Ubuntu server running Ubuntu 16.04.5 LTS. My PlayFramework version is 1.5.1.

I get the following error, and I cannot figure out why:

Nov 05 22:25:54 playframework[860]: SEVERE:
Nov 05 22:25:54 playframework[860]: @79nn5m673
Nov 05 22:25:54 playframework[860]: Failed to start
Nov 05 22:25:54 playframework[860]: Compilation error
Nov 05 22:25:54 playframework[860]: The file  could not be compiled. Error raised is : Java version prior to 1.8 are not supported
Nov 05 22:25:54 playframework[860]: play.exceptions.CompilationException: Java version prior to 1.8 are not supported
Nov 05 22:25:54 playframework[860]:         at play.classloading.ApplicationCompiler.<init>(ApplicationCompiler.java:64)
Nov 05 22:25:54 playframework[860]:         at play.classloading.ApplicationClasses.<init>(ApplicationClasses.java:29)
Nov 05 22:25:54 playframework[860]:         at play.Play.init(Play.java:219)
Nov 05 22:25:54 playframework[860]:         at play.server.Server.main(Server.java:162)

The Java version I am running is Oracle Java 1.8:

Java(TM) SE Runtime Environment (build 1.8.0_191-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.191-b12, mixed mode)

I have also tried Java 11, but get the same error:

javac 11.0.1

java 11.0.1 2018-10-16 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.1+13-LTS)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.1+13-LTS, mixed mode)

Under alternatives I get the following, showing no pre-1.8 java versions.

  Selection    Path                                            Priority   Status
------------------------------------------------------------
  0            /usr/lib/jvm/java-11-oracle/bin/java             1091      auto mode
* 1            /usr/lib/jvm/java-11-oracle/bin/java             1091      manual mode
  2            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1081      manual mode
  3            /usr/lib/jvm/java-8-oracle/jre/bin/java          1081      manual mode

Issuing the 'play run' command also confirms it is using Java 11:

~        _            _ 
~  _ __ | | __ _ _  _| |
~ | '_ \| |/ _' | || |_|
~ |  __/|_|\____|\__ (_)
~ |_|            |__/   
~
~ play! 1.5.1, https://www.playframework.com
~
~ Ctrl+C to stop
~ 
~ using java version "1.8.0_191"
Listening for transport dt_socket at address: 8000
Nov 05, 2018 10:37:44 PM play.Logger niceThrowable
SEVERE: 

@79nn7ahaj
Failed to start

Compilation error
The file  could not be compiled. Error raised is : Java version prior to 1.8 are not supported

play.exceptions.CompilationException: Java version prior to 1.8 are not supported
    at play.classloading.ApplicationCompiler.<init>(ApplicationCompiler.java:64)
    at play.classloading.ApplicationClasses.<init>(ApplicationClasses.java:29)
    at play.Play.init(Play.java:219)
    at play.server.Server.main(Server.java:162)
There must be a simple explanation for this, but I cannot find it.

Answer 1

The problem was the optional setting in the configuration file. The compiler version can be overruled there.