Java 11 support

[schabdo]

As Java 8-10 will be obsolete soon, hawkBit has to support Java 11

Preconditions

• Migration to Vaadin 8 (Migrated Hawkbit UI to Vaadin 8 #980)
• Required EclipseLink upgrade will brake SQLServer support (JPA Repository broken with SQLServer after Eclipselink update #1045, #964)
• Release 0.3.0 (on Java 8) (Release 0.3.0 #784)

ToDo

• JDK11 build on source level 8 (JDK 11 build support for hawkBit #1037)
• Migrate hawkBit (Java 11 support for hawkBit #1038)
• Migrate hawkBit Extensions (no action required)
• Migrate hawkBit Examples (no action required)
• Upgrade EclipseLink to 2.7.7+
• Bump Java source level to 11
• Update Dockerfiles
• CircleCI build on JDK 11
• Update Documentation

[bantu]

Attempting to compile master at eae34e6 using the compiler provided by the openjdk-11-jdk Debian 10 package fails with

[INFO] Compiling module org.eclipse.hawkbit.ui.AppWidgetSet
[INFO]    [ERROR] Hint: Check that your module inherits 'com.google.gwt.core.Core' either directly or indirectly (most often by inheriting module 'com.google.gwt.user.User')

On closer inspection this seems to be caused by GWT.

Maybe the Java 8 source code can be compiled using OpenJDK 11 after updating GWT. This would be a first step towards moving to Java 11 entirely.

[schabdo]

Exactly! I already prepared some stuff to achieve exactly what you're proposing (cf. #674). However back in the days (as you mentioned) Vaadin 7 was always the show-stopper. Since a couple of days master is on Vaadin 8, we are one step further: Now WidgetSet could be complied based on JDK 11 (with source level to 1.8). However it seems that the XML bind dependency/module is missing for the tests:

[ERROR] javax/xml/bind/annotation/XmlElement
[ERROR] org.apache.maven.surefire.booter.SurefireBooterForkException: There was an error in the forked process
[ERROR] javax/xml/bind/annotation/XmlElement
[ERROR] 	at org.apache.maven.plugin.surefire.booterclient.ForkStarter.fork(ForkStarter.java:656)

[avgustinmm]

Obsolete, hawkBit is supporting Java17 already