ci: using JDK 11 to compile and JDK 8 to run junit (8)

.github/workflows/ci.yaml

@@ -25,7 +25,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        java: [8, 11, 17]
+        java: [11, 17]
     steps:
     - uses: actions/checkout@v3
     - uses: actions/setup-java@v3
@@ -36,6 +36,24 @@ jobs:
     - run: .kokoro/build.sh
       env:
         JOB_TYPE: test
+  units-java8:
+    name: "units (8)"
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - uses: actions/setup-java@v3
+      with:
+        java-version: 8
+        distribution: zulu
+    - run: echo "JAVA8_HOME=${JAVA_HOME}" >> $GITHUB_ENV
+    - uses: actions/setup-java@v3
+      with:
+        java-version: 11
+        distribution: zulu
+    - run: echo "JAVA11_HOME=${JAVA_HOME}" >> $GITHUB_ENV
+    - run: .kokoro/build.sh
+      env:
+        JOB_TYPE: test
   windows:
     runs-on: windows-latest
     steps:

.kokoro/build.sh

@@ -23,6 +23,17 @@ cd ${scriptDir}/..
 # include common functions
 source ${scriptDir}/common.sh
 
+function setJava() {
+  export JAVA_HOME=$1
+  export PATH=${JAVA_HOME}/bin:$PATH
+}
+
+# units-java8 uses both JDK 11 and JDK 8. GraalVM dependencies require JDK 11 to
+# compile the classes touching GraalVM classes.
+if [ ! -z "${JAVA11_HOME}" ]; then
+  setJava "${JAVA11_HOME}"
+fi
+
 # Print out Maven & Java version
 mvn -version
 echo ${JOB_TYPE}
@@ -42,6 +53,12 @@ if [[ ! -z "${GOOGLE_APPLICATION_CREDENTIALS}" && "${GOOGLE_APPLICATION_CREDENTI
     export GOOGLE_APPLICATION_CREDENTIALS=$(realpath ${KOKORO_GFILE_DIR}/${GOOGLE_APPLICATION_CREDENTIALS})
 fi
 
+# units-java8 uses both JDK 11 and JDK 8. We ensure the generated class files
+# are compatible with Java 8 when running tests.
+if [ ! -z "${JAVA8_HOME}" ]; then
+  setJava "${JAVA8_HOME}"
+fi
+
 RETURN_CODE=0
 set +e
 

pom.xml

@@ -224,4 +224,17 @@
     </plugins>
   </reporting>
 
+  <profiles>
+    <profile>
+      <!-- JDK 9+ has the "release" option to ensure the generated bytecode is
+       compatible with Java 8. -->
+      <id>compiler-release-8</id>
+      <activation>
+        <jdk>[9,]</jdk>
+      </activation>
+      <properties>
+        <maven.compiler.release>8</maven.compiler.release>
+      </properties>
+    </profile>
+  </profiles>
 </project>