Adds a workflow to check built class release

.github/workflows/java8Check.yml

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+name: Check java class version
+on:
+  push:
+    branches:
+      - "*"
+  pull_request:
+    types: [opened, synchronize, reopened]
+jobs:
+  build:
+    name: Build and check
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0  # Shallow clones should be disabled for a better relevancy of analysis
+      - name: Set up JDK 17
+        uses: actions/setup-java@v4
+        with:
+          java-version: 17
+          distribution: 'zulu' # Alternative distribution options are available.
+      - name: Cache Maven packages
+        uses: actions/cache@v4
+        with:
+          path: ~/.m2
+          key: ${{ runner.os }}-m2-${{ hashFiles('**/pom.xml') }}
+          restore-keys: ${{ runner.os }}-m2
+      - name: Build and check
+        run: |
+          mvn -P sonar package
+          cd java8Test
+          mvn package
+
+          echo "checking ../javaluator-demo/target/javaluator-demo.jar"
+          java -jar target/javaReleaseTest.jar ../javaluator-demo/target/javaluator-demo.jar 52
+
+          # Let check the library itself in case demo pom points to an older release of the library
+          OUT="$(ls ../javaluator/target/javaluator*.jar | grep -v javadoc.jar | grep -v sources.jar)"
+          echo "checking $OUT"
+          java -jar target/javaReleaseTest.jar $OUT 52
+
+          OUT="$(ls ../javaluator-examples/target/javaluator-examples*.jar | grep -v javadoc.jar | grep -v sources.jar)"
+          echo "checking $OUT"
+          java -jar target/javaReleaseTest.jar $OUT 52

java8Test/README.md

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+This folder contains a program used by 'java8Check.yml' workflow to check if generated classes are compatible with a java 8 (the exact release is defined in the workflow) virtual machine.

java8Test/pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<groupId>com.fathzer</groupId>
+		<artifactId>parent-pom</artifactId>
+		<version>1.0.8</version>
+    	<relativePath></relativePath>
+	</parent>
+	<artifactId>java-release-test</artifactId>
+	<version>0.0.1</version>
+	<name>java-release-test</name>
+	<description>A program that tests a jar contains classes compatible with a
+		specific java release.</description>
+
+	<properties>
+		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+		<maven.source.skip>true</maven.source.skip>
+		<maven.javadoc.skip>true</maven.javadoc.skip>
+		<maven.install.skip>true</maven.install.skip>
+		<maven.deploy.skip>true</maven.deploy.skip>
+	</properties>
+
+	<build>
+		<plugins>
+			<plugin>
+				<artifactId>maven-shade-plugin</artifactId>
+				<version>3.4.1</version>
+				<configuration>
+					<finalName>javaReleaseTest</finalName>
+					<transformers>
+						<transformer
+							implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
+							<mainClass>com.fathzer.java.release.Check</mainClass>
+						</transformer>
+					</transformers>
+				</configuration>
+				<executions>
+					<execution>
+						<phase>package</phase>
+						<goals>
+							<goal>shade</goal>
+						</goals>
+					</execution>
+				</executions>
+			</plugin>
+		</plugins>
+	</build>
+</project>

java8Test/src/main/java/com/fathzer/java/release/Check.java

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+package com.fathzer.java.release;
+
+import java.io.DataInputStream;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.util.function.Predicate;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipInputStream;
+
+public class Check {
+	private static final String CLASS_SUFFIX = ".class";
+
+	public static void main(String[] args) {
+		try {
+			if (args.length!=2) {
+				throw new IllegalArgumentException("This program requires two arguments: a jar file path and a maximum class level");
+			}
+			final File jar = new File(args[0]);
+			final int maxRelease = Integer.parseInt(args[1]);
+			new Check().check(jar, maxRelease, s->s.endsWith("-info.class"));
+			System.out.println("ok");
+		} catch (Exception e) {
+			e.printStackTrace();
+			System.exit(1);
+		}
+	}
+
+	private void check(File jar, int maxRelease, Predicate<String> ignored) throws IOException {
+		try (ZipInputStream zip = new ZipInputStream(new FileInputStream(jar))) {
+			final DataInputStream data = new DataInputStream(zip);
+			for (ZipEntry entry = zip.getNextEntry(); entry!=null; entry = zip.getNextEntry()) {
+				if (!entry.isDirectory() && entry.getName().endsWith(CLASS_SUFFIX) && !ignored.test(entry.getName())) {
+					if (zip.skip(6)!=6) {
+						throw new IOException("End of file reached before major class version");
+					}
+					final int release = data.readUnsignedShort();
+					if (release>maxRelease) {
+						throw new IllegalArgumentException("The major class version of "+entry.getName()+" is "+release);
+					}
+				}
+			}
+		}
+	}
+
+
+}