Add serializers for unmodifiable and synchronized collections

src/com/esotericsoftware/kryo/serializers/SynchronizedCollectionSerializers.java

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+/* Copyright (c) 2008-2025, Nathan Sweet
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following
+ * disclaimer in the documentation and/or other materials provided with the distribution.
+ * - Neither the name of Esoteric Software nor the names of its contributors may be used to endorse or promote products derived
+ * from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
+ * SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */
+
+package com.esotericsoftware.kryo.serializers;
+
+import com.esotericsoftware.kryo.Kryo;
+import com.esotericsoftware.kryo.KryoException;
+import com.esotericsoftware.kryo.Serializer;
+import com.esotericsoftware.kryo.io.Input;
+import com.esotericsoftware.kryo.io.Output;
+import com.esotericsoftware.kryo.unsafe.UnsafeUtil;
+import com.esotericsoftware.minlog.Log;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.SortedMap;
+import java.util.SortedSet;
+import java.util.TreeMap;
+import java.util.TreeSet;
+import java.util.function.Function;
+
+/** Serializer for synchronized Collections and Maps created via Collections. */
+@SuppressWarnings({"rawtypes", "unchecked"})
+public class SynchronizedCollectionSerializers {
+
+	private static class Offset {
+		private static final long SOURCE_COLLECTION_FIELD_OFFSET;
+		private static final long SOURCE_MAP_FIELD_OFFSET;
+
+		static {
+			String clsName = "java.util.Collections$SynchronizedCollection";
+			try {
+				SOURCE_COLLECTION_FIELD_OFFSET = UnsafeUtil.objectFieldOffset(Class.forName(clsName).getDeclaredField("c"));
+			} catch (Exception e) {
+				Log.warn("Could not access source collection field in {}", clsName);
+				throw new KryoException(e);
+			}
+			clsName = "java.util.Collections$SynchronizedMap";
+			try {
+				SOURCE_MAP_FIELD_OFFSET = UnsafeUtil.objectFieldOffset(Class.forName(clsName).getDeclaredField("m"));
+			} catch (Exception e) {
+				Log.warn("Could not access source map field in {}", clsName);
+				throw new KryoException(e);
+			}
+		}
+	}
+
+	static final class SynchronizedCollectionSerializer extends CollectionSerializer<Collection> {
+		private final Function factory;
+		private final long offset;
+
+		public SynchronizedCollectionSerializer (Function factory, long offset) {
+			setAcceptsNull(false);
+			this.factory = factory;
+			this.offset = offset;
+		}
+
+		@Override
+		public void write (Kryo kryo, Output output, Collection collection) {
+			Object unwrapped = UnsafeUtil.getObject(collection, offset);
+			synchronized (collection) {
+				kryo.writeClassAndObject(output, unwrapped);
+			}
+		}
+
+		@Override
+		public Collection read (Kryo kryo, Input input, Class<? extends Collection> type) {
+			final Object sourceCollection = kryo.readClassAndObject(input);
+			return (Collection)factory.apply(sourceCollection);
+		}
+
+		@Override
+		public Collection copy (Kryo kryo, Collection original) {
+			synchronized (original) {
+				final Object collection = UnsafeUtil.getObject(original, offset);
+				return (Collection)factory.apply(kryo.copy(collection));
+			}
+		}
+	}
+
+	static final class SynchronizedMapSerializer extends MapSerializer<Map> {
+		private final Function factory;
+		private final long offset;
+
+		public SynchronizedMapSerializer (Function factory, long offset) {
+			setAcceptsNull(false);
+			this.factory = factory;
+			this.offset = offset;
+		}
+
+		@Override
+		public void write (Kryo kryo, Output output, Map map) {
+			Object unwrapped = UnsafeUtil.getObject(map, offset);
+			synchronized (map) {
+				kryo.writeClassAndObject(output, unwrapped);
+			}
+		}
+
+		@Override
+		public Map read (Kryo kryo, Input input, Class<? extends Map> type) {
+			final Object sourceMap = kryo.readClassAndObject(input);
+			return (Map)factory.apply(sourceMap);
+		}
+
+		@Override
+		public Map copy (Kryo kryo, Map original) {
+			synchronized (original) {
+				final Object map = UnsafeUtil.getObject(original, offset);
+				return (Map)factory.apply(kryo.copy(map));
+			}
+		}
+	}
+
+	private static Serializer<?> createSerializer (Map.Entry<Class<?>, Function> factory) {
+		if (Collection.class.isAssignableFrom(factory.getKey())) {
+			return new SynchronizedCollectionSerializer(factory.getValue(), Offset.SOURCE_COLLECTION_FIELD_OFFSET);
+		} else {
+			return new SynchronizedMapSerializer(factory.getValue(), Offset.SOURCE_MAP_FIELD_OFFSET);
+		}
+	}
+
+	static Map<Class<?>, Function> synchronizedFactories () {
+		final Map<Class<?>, Function> factories = new HashMap<>();
+		factories.put(
+			Collections.synchronizedCollection(Arrays.asList("")).getClass(),
+			o -> Collections.synchronizedCollection((Collection)o));
+		factories.put(
+			Collections.synchronizedList(new ArrayList<Void>()).getClass(),
+			o1 -> Collections.synchronizedList((List<?>)o1));
+		factories.put(
+			Collections.synchronizedList(new LinkedList<Void>()).getClass(),
+			o2 -> Collections.synchronizedList((List<?>)o2));
+		factories.put(
+			Collections.synchronizedSet(new HashSet<Void>()).getClass(),
+			o3 -> Collections.synchronizedSet((Set<?>)o3));
+		factories.put(
+			Collections.synchronizedSortedSet(new TreeSet<>()).getClass(),
+			o4 -> Collections.synchronizedSortedSet((SortedSet<?>)o4));
+		factories.put(
+			Collections.synchronizedMap(new HashMap<Void, Void>()).getClass(),
+			o5 -> Collections.synchronizedMap((Map)o5));
+		factories.put(
+			Collections.synchronizedSortedMap(new TreeMap<>()).getClass(),
+			o6 -> Collections.synchronizedSortedMap((SortedMap)o6));
+		return factories;
+	}
+
+	/** Registering serializers for synchronized Collections and Maps created via {@link Collections}.
+	 *
+	 * @see Collections#synchronizedCollection(Collection)
+	 * @see Collections#synchronizedList(List)
+	 * @see Collections#synchronizedSet(Set)
+	 * @see Collections#synchronizedSortedSet(SortedSet)
+	 * @see Collections#synchronizedMap(Map)
+	 * @see Collections#synchronizedSortedMap(SortedMap) **/
+	public static void registerSerializers (Kryo kryo) {
+		try {
+			for (Map.Entry<Class<?>, Function> factory : synchronizedFactories().entrySet()) {
+				kryo.register(factory.getKey(), createSerializer(factory));
+			}
+		} catch (Throwable t) {
+			Log.warn("Unable to register serializers for synchronized collections.", t);
+		}
+	}
+
+	/** Adding default serializers for synchronized Collections and Maps created via {@link Collections}.
+	 *
+	 * @see Collections#synchronizedCollection(Collection)
+	 * @see Collections#synchronizedList(List)
+	 * @see Collections#synchronizedSet(Set)
+	 * @see Collections#synchronizedSortedSet(SortedSet)
+	 * @see Collections#synchronizedMap(Map)
+	 * @see Collections#synchronizedSortedMap(SortedMap) **/
+	public static void addDefaultSerializers (Kryo kryo) {
+		try {
+			for (Map.Entry<Class<?>, Function> factory : synchronizedFactories().entrySet()) {
+				kryo.addDefaultSerializer(factory.getKey(), createSerializer(factory));
+			}
+		} catch (Throwable t) {
+			Log.warn("Unable to add default serializers for synchronized collections.", t);
+		}
+	}
+}