feat: use Java 11 as compiler target (#341)

* feat: declare java 11 as source target
* ci: use JDK11 in Jenkins pipeline
* doc: adjust Java version in README
* ci: adjust Github action

.github/workflows/maven.yml

@@ -16,9 +16,9 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
-    - name: Set up JDK 1.8
+    - name: Set up JDK 11
       uses: actions/setup-java@v1
       with:
-        java-version: 1.8
+        java-version: 11
     - name: Build with Maven
       run: mvn -B package --file pom.xml

Jenkinsfile

@@ -8,7 +8,7 @@ kind: Pod
 spec:
   containers:
   - name: maven-sumo
-    image: eclipsemosaic/mosaic-ci:jdk8-sumo-1.18.0
+    image: eclipsemosaic/mosaic-ci:jdk11-sumo-1.18.0
     command:
     - cat
     tty: true

README.md

@@ -60,7 +60,7 @@ For further questions we are available via [email protected]
 For a successful build you need the following software to be installed:
 
 * **Maven 3.1.x** or higher.
-* **Java 8, 11, or 17** - We recommend using the [Adoptium OpenJDK (aka Eclipse Temurin)](https://adoptium.net/?variant=openjdk8).
+* **Java 11, or 17** - We recommend using the [Adoptium OpenJDK (aka Eclipse Temurin)](https://adoptium.net/?variant=openjdk11).
 * **SUMO 1.18.0** - Additionally, the environment variable `SUMO_HOME` should be configured properly.
 
 ## Build

pom.xml

@@ -81,7 +81,7 @@
     <properties>
         <mosaic.version>23.1-SNAPSHOT</mosaic.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <project.build.sourceTarget>1.8</project.build.sourceTarget>
+        <project.build.sourceTarget>11</project.build.sourceTarget>
         <skip.coverage>true</skip.coverage>
         <skip.javadoc>true</skip.javadoc>
         <version.commons-cli>1.4</version.commons-cli><!-- 1.4 is approved in CQ19371 -->

test/ci/ci-image-mvn-sumo/Dockerfile

@@ -1,4 +1,4 @@
-FROM maven:3.6.3-adoptopenjdk-8
+FROM maven:3.6.3-adoptopenjdk-11
 
 ENV DEBIAN_FRONTEND=noninteractive
 ENV USER_NAME=jenkins

test/ci/ci-image-mvn-sumo/README.md

@@ -10,9 +10,9 @@ build and tag the docker image with the latest SUMO version. This image should b
 and available in the PPA.
 
 ```shell script
-docker build . -t eclipsemosaic/mosaic-ci:jdk8-sumo-1.18.0
+docker build . -t eclipsemosaic/mosaic-ci:jdk11-sumo-1.18.0
 docker login
-docker push eclipsemosaic/mosaic-ci:jdk8-sumo-1.18.0
+docker push eclipsemosaic/mosaic-ci:jdk11-sumo-1.18.0
 ```  
 
 Afterwards, the image should be available here: https://hub.docker.com/r/eclipsemosaic/mosaic-ci/tags