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Fork of Esoteric Software's Kryo built by Nathan Sweet that replaces Minlog with slf4j as the logging facade. This contains the shaded reflectasm jar to prevent conflicts with other versions of asm.
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/* Copyright (c) 2008, 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 java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Field;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.esotericsoftware.kryo.Kryo;
import com.esotericsoftware.kryo.KryoException;
import com.esotericsoftware.kryo.io.Input;
import com.esotericsoftware.kryo.io.Output;

/** Serializes objects using direct field assignment, with versioning backward compatibility. Fields can be added without
 * invalidating previously serialized bytes. Note that removing, renaming or changing the type of a field is not supported. In
 * addition, forward compatibility is not supported.
 * 
 * There is a little additional overhead compared to {@link FieldSerializer}. A version varint is written before each object. When
 * deserializing, the input version will be examined to decide what fields are not in the input.
 * @author Tianyi HE  */
public class VersionFieldSerializer extends FieldSerializer {
	private static final Logger LOGGER = LoggerFactory.getLogger(VersionFieldSerializer.class);
	
	private int typeVersion = 0; // Version of current type.
	private int[] fieldVersion; // Version of each field.
	private boolean compatible = true; // Whether current type is compatible with serialized objects with different version.

	public VersionFieldSerializer (Kryo kryo, Class type) {
		super(kryo, type);
		// Make sure this is done before any read / write operations.
		initializeCachedFields();
	}

	public VersionFieldSerializer (Kryo kryo, Class type, boolean compatible) {
		this(kryo, type);
		this.compatible = compatible;
	}

	@Override
	protected void initializeCachedFields () {
		CachedField[] fields = getFields();
		fieldVersion = new int[fields.length];
		for (int i = 0, n = fields.length; i < n; i++) {
			Field field = fields[i].getField();
			Since since = field.getAnnotation(Since.class);
			if (since != null) {
				fieldVersion[i] = since.value();
				// Use the maximum version among fields as the entire type's version.
				typeVersion = Math.max(fieldVersion[i], typeVersion);
			} else {
				fieldVersion[i] = 0;
			}
		}
		this.removedFields.clear();
		LOGGER.debug("initializeCachedFields : Version for type {} is {}", getType().getName(), typeVersion);
	}

	@Override
	public void removeField (String fieldName) {
		super.removeField(fieldName);
		initializeCachedFields();
	}

	@Override
	public void removeField (CachedField field) {
		super.removeField(field);
		initializeCachedFields();
	}

	@Override
	public void write (Kryo kryo, Output output, T object) {
		CachedField[] fields = getFields();
		// Write type version.
		output.writeVarInt(typeVersion, true);
		// Write fields.
		for (int i = 0, n = fields.length; i < n; i++) {
			fields[i].write(output, object);
		}
	}

	@Override
	public T read (Kryo kryo, Input input, Class type) {
		T object = create(kryo, input, type);
		kryo.reference(object);

		// Read input version.
		int version = input.readVarInt(true);
		if (!compatible && version != typeVersion) {
			// Reject to read
			throw new KryoException("Version not compatible: " + version + " <-> " + typeVersion);
		}
		CachedField[] fields = getFields();
		for (int i = 0, n = fields.length; i < n; i++) {
			// Field is not present in input, skip it.
			if (fieldVersion[i] > version) {
				LOGGER.debug("read : Skip field {}", fields[i].getField().getName());
				continue;
			}
			fields[i].read(input, object);
		}
		return object;
	}

	/** Incremental modification of serialized objects must add {@link Since} for new fields. */
	@Retention(RetentionPolicy.RUNTIME)
	@Target(ElementType.FIELD)
	public @interface Since {
		/** Version of annotated field, default is 0, and must be incremental to maintain compatibility. */
		int value() default 0;
	}
}