Java 9 support: use Unsafe-based reflection in Java 9+ (google#1218)

* Java 9 support: use Unsafe-based reflection in Java 9+

fixes "illegal reflective access" warnings and exceptions

* fix Codacy warnings

* improve code quality based on PR review

* improve code quality based on PR review

* fix Codacy warning

* improve code quality based on PR review

* inlined createReflectionAccessor method

gson/src/main/java/com/google/gson/internal/ConstructorConstructor.java

@@ -40,13 +40,15 @@
 
 import com.google.gson.InstanceCreator;
 import com.google.gson.JsonIOException;
+import com.google.gson.internal.reflect.ReflectionAccessor;
 import com.google.gson.reflect.TypeToken;
 
 /**
  * Returns a function that can construct an instance of a requested type.
  */
 public final class ConstructorConstructor {
   private final Map<Type, InstanceCreator<?>> instanceCreators;
+  private final ReflectionAccessor accessor = ReflectionAccessor.getInstance();
 
   public ConstructorConstructor(Map<Type, InstanceCreator<?>> instanceCreators) {
     this.instanceCreators = instanceCreators;
@@ -98,7 +100,7 @@ private <T> ObjectConstructor<T> newDefaultConstructor(Class<? super T> rawType)
     try {
       final Constructor<? super T> constructor = rawType.getDeclaredConstructor();
       if (!constructor.isAccessible()) {
-        constructor.setAccessible(true);
+        accessor.makeAccessible(constructor);
       }
       return new ObjectConstructor<T>() {
         @SuppressWarnings("unchecked") // T is the same raw type as is requested

gson/src/main/java/com/google/gson/internal/bind/ReflectiveTypeAdapterFactory.java

@@ -28,6 +28,7 @@
 import com.google.gson.internal.Excluder;
 import com.google.gson.internal.ObjectConstructor;
 import com.google.gson.internal.Primitives;
+import com.google.gson.internal.reflect.ReflectionAccessor;
 import com.google.gson.reflect.TypeToken;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonToken;
@@ -49,6 +50,7 @@ public final class ReflectiveTypeAdapterFactory implements TypeAdapterFactory {
   private final FieldNamingStrategy fieldNamingPolicy;
   private final Excluder excluder;
   private final JsonAdapterAnnotationTypeAdapterFactory jsonAdapterFactory;
+  private final ReflectionAccessor accessor = ReflectionAccessor.getInstance();
 
   public ReflectiveTypeAdapterFactory(ConstructorConstructor constructorConstructor,
       FieldNamingStrategy fieldNamingPolicy, Excluder excluder,
@@ -154,7 +156,7 @@ private Map<String, BoundField> getBoundFields(Gson context, TypeToken<?> type,
         if (!serialize && !deserialize) {
           continue;
         }
-        field.setAccessible(true);
+        accessor.makeAccessible(field);
         Type fieldType = $Gson$Types.resolve(type.getType(), raw, field.getGenericType());
         List<String> fieldNames = getFieldNames(field);
         BoundField previous = null;

gson/src/main/java/com/google/gson/internal/reflect/PreJava9ReflectionAccessor.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2017 The Gson authors
+ *
+ * Licensed 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 com.google.gson.internal.reflect;
+
+import java.lang.reflect.AccessibleObject;
+
+/**
+ * A basic implementation of {@link ReflectionAccessor} which is suitable for Java 8 and below.
+ * <p>
+ * This implementation just calls {@link AccessibleObject#setAccessible(boolean) setAccessible(true)}, which worked
+ * fine before Java 9.
+ */
+final class PreJava9ReflectionAccessor extends ReflectionAccessor {
+
+  /**
+   * {@inheritDoc}
+   */
+  @Override
+  public void makeAccessible(AccessibleObject ao) {
+    ao.setAccessible(true);
+  }
+
+}

gson/src/main/java/com/google/gson/internal/reflect/ReflectionAccessor.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2017 The Gson authors
+ *
+ * Licensed 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 com.google.gson.internal.reflect;
+
+import com.google.gson.util.VersionUtils;
+
+import java.lang.reflect.AccessibleObject;
+
+/**
+ * Provides a replacement for {@link AccessibleObject#setAccessible(boolean)}, which may be used to
+ * avoid reflective access issues appeared in Java 9, like {@link java.lang.reflect.InaccessibleObjectException}
+ * thrown or warnings like
+ * <pre>
+ *   WARNING: An illegal reflective access operation has occurred
+ *   WARNING: Illegal reflective access by ...
+ * </pre>
+ * <p/>
+ * Works both for Java 9 and earlier Java versions.
+ */
+public abstract class ReflectionAccessor {
+
+  // the singleton instance, use getInstance() to obtain
+  private static final ReflectionAccessor instance = VersionUtils.getMajorJavaVersion() < 9 ? new PreJava9ReflectionAccessor() : new UnsafeReflectionAccessor();
+
+  /**
+   * Does the same as {@code ao.setAccessible(true)}, but never throws
+   * {@link java.lang.reflect.InaccessibleObjectException}
+   */
+  public abstract void makeAccessible(AccessibleObject ao);
+
+  /**
+   * Obtains a {@link ReflectionAccessor} instance suitable for the current Java version.
+   * <p>
+   * You may need one a reflective operation in your code throws {@link java.lang.reflect.InaccessibleObjectException}.
+   * In such a case, use {@link ReflectionAccessor#makeAccessible(AccessibleObject)} on a field, method or constructor
+   * (instead of basic {@link AccessibleObject#setAccessible(boolean)}).
+   */
+  public static ReflectionAccessor getInstance() {
+    return instance;
+  }
+}

gson/src/main/java/com/google/gson/internal/reflect/UnsafeReflectionAccessor.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2017 The Gson authors
+ *
+ * Licensed 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 com.google.gson.internal.reflect;
+
+import sun.misc.Unsafe;
+
+import java.lang.reflect.AccessibleObject;
+import java.lang.reflect.Field;
+
+/**
+ * An implementation of {@link ReflectionAccessor} based on {@link Unsafe}.
+ * <p>
+ * NOTE: This implementation is designed for Java 9. Although it should work with earlier Java releases, it is better to
+ * use {@link PreJava9ReflectionAccessor} for them.
+ */
+final class UnsafeReflectionAccessor extends ReflectionAccessor {
+
+  private final Unsafe theUnsafe = getUnsafeInstance();
+  private final Field overrideField = getOverrideField();
+
+  /**
+   * {@inheritDoc}
+   */
+  @Override
+  public void makeAccessible(AccessibleObject ao) {
+    if (theUnsafe != null && overrideField != null) {
+      long overrideOffset = theUnsafe.objectFieldOffset(overrideField);
+      theUnsafe.putBoolean(ao, overrideOffset, true);
+    }
+  }
+
+  private static Unsafe getUnsafeInstance() {
+    try {
+      Field unsafeField = Unsafe.class.getDeclaredField("theUnsafe");
+      unsafeField.setAccessible(true);
+      return (Unsafe) unsafeField.get(null);
+    } catch (Exception e) {
+      e.printStackTrace();
+      return null;
+    }
+  }
+
+  private static Field getOverrideField() {
+    try {
+      return AccessibleObject.class.getDeclaredField("override");
+    } catch (NoSuchFieldException e) {
+      e.printStackTrace();
+      return null;
+    }
+  }
+}

gson/src/main/java/com/google/gson/reflect/package-info.java

@@ -1,6 +1,6 @@
 /**
  * This package provides utility classes for finding type information for generic types.
- *  
+ *
  * @author Inderjeet Singh, Joel Leitch
  */
 package com.google.gson.reflect;