geode-core/src/main/java/org/apache/geode/CanonicalInstantiator.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.IOException;

/**
 * <code>CanonicalInstantiator</code> is much like its parent <code>Instantiator</code> except that
 * instead of needing to implement <code>newInstance()</code> you now must implement
 * <code>newInstance(DataInput)</code>. The addition of the <code>DataInput</code> parameter allows
 * the instance creator to optionally read data from the data input stream and use it to decide the
 * instance to create. This allows a value that represents a canonical instance to be written by a
 * class's {@link DataSerializer#toData} and then be read by <code>newInstance(DataInput)</code> and
 * map it back to a canonical instance.
 * <p>
 * Note that {@link DataSerializer#fromData} is always called on the instance returned from
 * <code>newInstance(DataInput)</code>.
 *
 * @since GemFire 5.1
 */
public abstract class CanonicalInstantiator extends Instantiator {

  /**
   * Creates a new <code>CanonicalInstantiator</code> that instantiates a given class.
   *
   * @param c The <code>DataSerializable</code> class to register. This class must have a static
   *        initializer that registers this <code>Instantiator</code>.
   * @param classId A unique id for class <code>c</code>. The <code>classId</code> must not be zero.
   *        This has been an <code>int</code> since dsPhase1.
   *
   * @throws IllegalArgumentException If <code>c</code> does not implement
   *         <code>DataSerializable</code>, <code>classId</code> is less than or equal to zero.
   * @throws NullPointerException If <code>c</code> is <code>null</code>
   */
  public CanonicalInstantiator(Class<? extends DataSerializable> c, int classId) {
    super(c, classId);
  }

  /**
   * This method is not supported and if called will throw UnsupportedOperationException. Use
   * {@link #newInstance(DataInput)} instead.
   *
   * @throws UnsupportedOperationException in all cases
   */
  @Override
  public DataSerializable newInstance() {
    throw new UnsupportedOperationException();
  }

  /**
   * Creates a new "empty" instance of a <Code>DataSerializable</code> class whose state will be
   * filled in by invoking its {@link DataSerializable#fromData fromData} method.
   *
   * @param in the data input that can be read to decide what instance to create.
   * @return the new "empty" instance.
   * @throws IOException if a read from <code>in</code> fails.
   * @since GemFire 5.1
   */
  public abstract DataSerializable newInstance(DataInput in) throws IOException;
}