Statically linked JavaNImpl classes, utilizing "JEP 238: Multi-Releas…

…e JAR Files"

build.gradle.kts

@@ -20,7 +20,7 @@
 import java.io.FileOutputStream
 import java.nio.charset.StandardCharsets
 import java.nio.file.Files
-import java.util.Properties
+import java.util.*
 import java.util.stream.Collectors
 
 plugins {
@@ -144,6 +144,9 @@ tasks.sourcesJar.configure {
         into("META-INF")
     }
 
+    exclude("freemarker/core/_Java9Impl.java")
+    exclude("freemarker/core/_Java16Impl.java")
+
     // Depend on the createBuildInfo task and include the generated file
     dependsOn(createBuildInfo)
     from(buildInfoFile())

freemarker-core/src/main/java/freemarker/core/_Java16.java

@@ -26,6 +26,15 @@
  * Used for accessing functionality that's only present in Java 16 or later.
  */
 public interface _Java16 {
+    /**
+     * Using "JEP 238: Multi-Release JAR Files", links to the proper version of the {@link _Java16Impl} class.
+     */
+    _Java16 INSTANCE = new _Java16Impl();
+
+    /**
+     * Tells if Java 16 features can be used in the current run-time environment.
+     */
+    boolean isSupported();
 
     boolean isRecord(Class<?> cl);
 

freemarker-core/src/main/java/freemarker/core/_Java16Impl.java

@@ -0,0 +1,50 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package freemarker.core;
+
+import java.lang.reflect.Method;
+import java.util.Set;
+
+/**
+ * Used internally only, might change without notice!
+ * Pre-Java-16 implementation of {@link _Java16}.
+ */
+// We also have a Java 16 versions of this class in freemarker-core16, and we put all versions into
+// the jar artifact via "JEP 238: Multi-Release JAR Files".
+public final class _Java16Impl implements _Java16 {
+    @Override
+    public boolean isSupported() {
+        return false;
+    }
+
+    @Override
+    public boolean isRecord(Class<?> cl) {
+        throw newNoRecordSupportException();
+    }
+
+    @Override
+    public Set<Method> getComponentAccessors(Class<?> recordClass){
+        throw newNoRecordSupportException();
+    }
+
+    private UnsupportedOperationException newNoRecordSupportException() {
+        return new UnsupportedOperationException("Record support needs at least Java 16");
+    }
+}

freemarker-core/src/main/java/freemarker/core/_Java9.java

@@ -23,6 +23,15 @@
  * Used for accessing functionality that's only present in Java 9 or later.
  */
 public interface _Java9 {
+    /**
+     * Using "JEP 238: Multi-Release JAR Files", links to the proper version of the {@link _Java9Impl} class.
+     */
+    _Java9 INSTANCE = new _Java9Impl();
+
+    /**
+     * Tells if Java 9 features can be used in the current run-time environment.
+     */
+    boolean isSupported();
 
     boolean isAccessibleAccordingToModuleExports(Class<?> m);
 

freemarker-core/src/main/java/freemarker/core/_Java9Impl.java

@@ -0,0 +1,38 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package freemarker.core;
+
+/**
+ * Used internally only, might change without notice!
+ * Pre-Java-9 implementation of {@link _Java9}.
+ */
+// We also have a Java 9 versions of this class in freemarker-core9, and we put all versions into
+// the jar artifact via "JEP 238: Multi-Release JAR Files".
+public class _Java9Impl implements _Java9 {
+    @Override
+    public boolean isSupported() {
+        return false;
+    }
+
+    @Override
+    public boolean isAccessibleAccordingToModuleExports(Class<?> m) {
+        throw new UnsupportedOperationException("Requires at least Java 9");
+    }
+}

freemarker-core/src/main/java/freemarker/ext/beans/ClassIntrospector.java

@@ -48,7 +48,8 @@
 import java.util.concurrent.ConcurrentHashMap;
 
 import freemarker.core.BugException;
-import freemarker.core._JavaVersions;
+import freemarker.core._Java16;
+import freemarker.core._Java9;
 import freemarker.ext.beans.BeansWrapper.MethodAppearanceDecision;
 import freemarker.ext.beans.BeansWrapper.MethodAppearanceDecisionInput;
 import freemarker.ext.util.ModelCache;
@@ -200,7 +201,7 @@ class ClassIntrospector {
         this.defaultZeroArgumentNonVoidMethodPolicy = builder.getDefaultZeroArgumentNonVoidMethodPolicy();
         this.recordZeroArgumentNonVoidMethodPolicy = builder.getRecordZeroArgumentNonVoidMethodPolicy();
         this.recordAware = defaultZeroArgumentNonVoidMethodPolicy != recordZeroArgumentNonVoidMethodPolicy;
-        if (recordAware && _JavaVersions.JAVA_16 == null) {
+        if (recordAware && !_Java16.INSTANCE.isSupported()) {
             throw new IllegalArgumentException(
                     "defaultZeroArgumentNonVoidMethodPolicy != recordZeroArgumentNonVoidMethodPolicy, " +
                     "but record support is not available (as Java 16 support is not available).");
@@ -343,7 +344,7 @@ private void addBeanInfoToClassIntrospectionData(
             ClassMemberAccessPolicy effClassMemberAccessPolicy) throws IntrospectionException {
         BeanInfo beanInfo = Introspector.getBeanInfo(clazz);
 
-        boolean treatClassAsRecord = recordAware && _JavaVersions.JAVA_16.isRecord(clazz);
+        boolean treatClassAsRecord = recordAware && _Java16.INSTANCE.isRecord(clazz);
         ZeroArgumentNonVoidMethodPolicy zeroArgumentNonVoidMethodPolicy = treatClassAsRecord
                 ? recordZeroArgumentNonVoidMethodPolicy
                 : defaultZeroArgumentNonVoidMethodPolicy;
@@ -835,7 +836,7 @@ private static Map<ExecutableMemberSignature, List<Method>> discoverAccessibleMe
     private static void discoverAccessibleMethods(
             Class<?> clazz, Map<ExecutableMemberSignature, List<Method>> accessibles) {
         if (Modifier.isPublic(clazz.getModifiers())
-                && (_JavaVersions.JAVA_9 == null || _JavaVersions.JAVA_9.isAccessibleAccordingToModuleExports(clazz))) {
+                && (!_Java9.INSTANCE.isSupported() || _Java9.INSTANCE.isAccessibleAccordingToModuleExports(clazz))) {
             try {
                 Method[] methods = clazz.getMethods();
                 for (int i = 0; i < methods.length; i++) {

freemarker-core/src/main/java/freemarker/ext/beans/ClassIntrospectorBuilder.java

@@ -26,7 +26,7 @@
 import java.util.Iterator;
 import java.util.Map;
 
-import freemarker.core._JavaVersions;
+import freemarker.core._Java16;
 import freemarker.template.Configuration;
 import freemarker.template.Version;
 import freemarker.template._TemplateAPI;
@@ -76,9 +76,10 @@ final class ClassIntrospectorBuilder implements Cloneable {
         this.incompatibleImprovements = normalizeIncompatibleImprovementsVersion(incompatibleImprovements);
         treatDefaultMethodsAsBeanMembers = incompatibleImprovements.intValue() >= _VersionInts.V_2_3_26;
         defaultZeroArgumentNonVoidMethodPolicy = ZeroArgumentNonVoidMethodPolicy.METHOD_ONLY;
-        recordZeroArgumentNonVoidMethodPolicy = incompatibleImprovements.intValue() >= _VersionInts.V_2_3_33 && _JavaVersions.JAVA_16 != null
-                ? ZeroArgumentNonVoidMethodPolicy.BOTH_METHOD_AND_PROPERTY_UNLESS_BEAN_PROPERTY_READ_METHOD
-                : defaultZeroArgumentNonVoidMethodPolicy;
+        recordZeroArgumentNonVoidMethodPolicy
+                = incompatibleImprovements.intValue() >= _VersionInts.V_2_3_33 && _Java16.INSTANCE.isSupported()
+                        ? ZeroArgumentNonVoidMethodPolicy.BOTH_METHOD_AND_PROPERTY_UNLESS_BEAN_PROPERTY_READ_METHOD
+                        : defaultZeroArgumentNonVoidMethodPolicy;
         memberAccessPolicy = DefaultMemberAccessPolicy.getInstance(this.incompatibleImprovements);
     }
 

freemarker-core16/src/main/java/freemarker/core/_Java16Impl.java

@@ -25,16 +25,15 @@
 
 /**
  * Used internally only, might change without notice!
- * Used for accessing functionality that's only present in Java 16 or later.
+ * Java 16 implementation of {@link _Java16}.
  */
-// Compile this against Java 16
+// We also have a pre-Java-16 versions of this class in freemarker-core, and we put all versions into
+// the jar artifact via "JEP 238: Multi-Release JAR Files".
 @SuppressWarnings("Since15") // For IntelliJ inspection
 public class _Java16Impl implements _Java16 {
-
-    public static final _Java16 INSTANCE = new _Java16Impl();
-
-    private _Java16Impl() {
-        // Not meant to be instantiated
+    @Override
+    public boolean isSupported() {
+        return true;
     }
 
     @Override

freemarker-core16/src/test/java/freemarker/ext/beans/Java16TestClassLoadingCorrectTest.java

@@ -0,0 +1,37 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package freemarker.ext.beans;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+import freemarker.core._Java16;
+import freemarker.core._Java16Impl;
+
+public class Java16TestClassLoadingCorrectTest {
+    @Test
+    public void java16Supported() {
+        // This can be a problem if the test is not ran from the jar, and the impl class from the core takes precedence
+        assertTrue(
+                "Multi-Release JAR selection of the proper " + _Java16Impl.class.getName() + " variant didn't happen in the Java 16 test environment",
+                _Java16.INSTANCE.isSupported());
+    }
+}

freemarker-core16/src/test/java/freemarker/ext/beans/NotExportedInternalPackageTest.java

@@ -33,6 +33,7 @@
 import org.w3c.dom.Document;
 import org.xml.sax.InputSource;
 
+import freemarker.core._Java16;
 import freemarker.template.TemplateHashModel;
 import freemarker.template.TemplateMethodModelEx;
 
@@ -42,6 +43,8 @@
 public class NotExportedInternalPackageTest {
     @Test
     public void java16InternalClassAvoidanceTest() throws Exception {
+        assertTrue(_Java16.INSTANCE.isSupported());
+
         BeansWrapper bw = new BeansWrapper();
 
         Document document = DocumentBuilderFactory.newInstance().newDocumentBuilder()

freemarker-core9/src/main/java/freemarker/core/_Java9Impl.java

@@ -22,18 +22,17 @@
 
 /**
  * Used internally only, might change without notice!
- * Used for accessing functionality that's only present in Java 9 or later.
+ * Java 9 implementation of {@link _Java9}.
  */
-// Compile this against Java 9
+// We also have a pre-Java-9 versions of this class in freemarker-core, and we put all versions into
+// the jar artifact via "JEP 238: Multi-Release JAR Files".
 @SuppressWarnings("Since15") // For IntelliJ inspection
 public class _Java9Impl implements _Java9 {
-
-    public static final _Java9 INSTANCE = new _Java9Impl();
-
     private static final Module ACCESSOR_MODULE = BeansWrapper.class.getModule();
 
-    private _Java9Impl() {
-        // Not meant to be instantiated
+    @Override
+    public boolean isSupported() {
+        return true;
     }
 
     @Override