geode-core/src/main/java/org/apache/geode/DataSerializable.java

/*
 * 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 org.apache.geode;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.io.Serializable;


/**
 * An interface for objects whose state can be written/read as primitive types and strings ("data").
 * That is, instead of serializing itself to an {@link java.io.ObjectOutputStream}, a
 * <code>DataSerializable</code> can serialize itself to a {@link DataOutput}. By implementing this
 * interface, objects can be serialized faster and in a more compact format than standard Java
 * serialization. The {@link DataSerializer} class contains a number of static methods that may be
 * helpful to implementations of <code>DataSerializable</code>.
 *
 * <P>
 *
 * When possible, GemFire respects the <code>DataSerializable</code> contract to provide optimal
 * object serialization. For instance, if a <code>DataSerializable</code> object is
 * {@linkplain org.apache.geode.cache.Region#put(Object, Object) placed} into a distributed cache
 * region, its <code>toData</code> method will be used to serialize it when it is sent to another
 * member of the distributed system.
 *
 * <P>
 *
 * To avoid the overhead of Java reflection, <code>DataSerializable</code> classes may register an
 * {@link Instantiator} to be used during deserialization. Alternatively, classes that implement
 * <code>DataSerializable</code> can provide a zero-argument constructor that will be invoked when
 * they are read with {@link DataSerializer#readObject}.
 *
 * <P>
 *
 * Some classes (especially third-party classes that you may not have the source code to) cannot be
 * modified to implement <code>DataSerializable</code>. These classes can be data serialized by an
 * instance of {@link DataSerializer}.
 *
 * <P>
 *
 * <code>DataSerializable</code> offers improved performance over standard Java serialization, but
 * does not offer all of the features of standard Java serialization. In particular, data
 * serialization does not attempt to maintain referential integrity among the objects it is writing
 * or reading. As a result, data serialization should not be used with complex object graphs.
 * Attempting to data serialize graphs that contain object cycles will result in infinite recursion
 * and a {@link StackOverflowError}. Attempting to deserialize an object graph that contains
 * multiple reference paths to the same object will result in multiple copies of the objects that
 * are referred to through multiple paths.
 *
 * <P>
 *
 * <CENTER>
 * <IMG src="{@docRoot}/javadoc-images/data-serialization-exceptions.gif" HEIGHT="219" WIDTH="698">
 * </CENTER>
 *
 * @see java.io.Serializable
 * @see DataSerializer
 * @see Instantiator
 *
 * @since GemFire 3.5
 */
public interface DataSerializable extends Serializable {

  /**
   * Writes the state of this object as primitive data to the given <code>DataOutput</code>.
   * <p>
   * Since 5.7 it is possible for any method call to the specified <code>DataOutput</code> to throw
   * {@link GemFireRethrowable}. It should <em>not</em> be caught by user code. If it is it
   * <em>must</em> be rethrown.
   *
   * @throws IOException A problem occurs while writing to <code>out</code>
   */
  void toData(DataOutput out) throws IOException;

  /**
   * Reads the state of this object as primitive data from the given <code>DataInput</code>.
   *
   * @throws IOException A problem occurs while reading from <code>in</code>
   * @throws ClassNotFoundException A class could not be loaded while reading from <code>in</code>
   */
  void fromData(DataInput in) throws IOException, ClassNotFoundException;

  //////////////////////// Inner Classes ////////////////////////

  /**
   * <code>Replaceable</code> allows an object to write an alternative version of itself to a
   * <code>DataOutput</code>. It is similar to the <code>writeReplace</code> method of standard Java
   * {@linkplain java.io.Serializable serialization}.
   *
   * <P>
   *
   * Note that if a <code>Replaceable</code> is also <code>DataSerializable</code>, its
   * <code>toData</code> method will <B>not</B> be invoked. Instead, its replacement object will be
   * written to the stream using {@link DataSerializer#writeObject(Object, DataOutput)}.
   *
   * @see DataSerializer#writeObject(Object, DataOutput)
   */
  interface Replaceable {

    /**
     * Replaces this object with another in the "output stream" written by
     * {@link DataSerializer#writeObject(Object, DataOutput)}.
     */
    Object replace() throws IOException;
  }

}