src/java/org/apache/hadoop/io/serial/Serialization.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.hadoop.io.serial;

import java.io.DataInput;
import java.io.DataInputStream;
import java.io.DataOutput;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;

/**
 * The primary interface to provide serialization.
 * @param <T> the parent type that it will serialize
 */
@InterfaceAudience.Public
@InterfaceStability.Stable
public abstract class Serialization<T> implements Cloneable {
  
  /**
   * Serialize the given object to the OutputStream.
   * @param stream the stream to serialize to
   * @param object the object to serialize
   * @throws IOException if the serialization fails
   */
  public abstract void serialize(OutputStream stream, 
                                 T object) throws IOException;

  /**
   * Deserialize the given object from the InputStream.
   * @param stream the stream to deserialize from
   * @param reusableObject an object (or null) that may be reused by the 
   *        serializer
   * @param conf the user's configuration
   * @return the object that was created or reused with the data in it
   * @throws IOException if the deserialization fails
   */
  public abstract T deserialize(InputStream stream,
                                T reusableObject,
                                Configuration conf) throws IOException;
  
  /**
   * Get the default raw comparator for the given serializer
   * @return a comparator that will compare bytes
   */
  public abstract RawComparator getRawComparator();
  
  /**
   * Serialize the serializer's configuration to the output stream.
   * @param out the stream to serialize to
   * @throws IOException if the serialization fails
   */
  public abstract void serializeSelf(OutputStream out) throws IOException;
  
  /**
   * Modify the serialization's configuration to reflect the contents of the
   * input stream.
   * @param in the stream to read from
   * @param conf the configuration
   * @throws IOException if the deserialization fails
   */
  public abstract void deserializeSelf(InputStream in,
                                       Configuration conf) throws IOException;
  
  /**
   * Generate the state of the serialization in a human-friendly string.
   * @return the textual representation of the serialization state
   */
  @Override
  public abstract String toString();

  /**
   * Restore the state of the serialization from a human-friendly string.
   * @param metadata the string that was generated by toString
   * @throws IOException
   */
  public abstract void fromString(String metadata) throws IOException;
  
  /**
   * Get the name for this kind of serialization, which must be unique. This 
   * name is used to identify the serialization that was used to write a
   * particular file.
   * @return the unique name
   */
  public String getName() {
    return getClass().getName();
  }
  
  /**
   * Ensure the InputStream is a DataInput, wrapping it if necessary
   * @param in the input stream to wrap
   * @return the wrapped stream
   */
  protected DataInput ensureDataInput(InputStream in) {
    if (in instanceof DataInput) {
      return (DataInput) in;
    } else {
      return new DataInputStream(in);
    }
  }

  /**
   * Ensure the OutputStream is a DataOutput, wrapping it if necessary.
   * @param out the output stream to wrap
   * @return the wrapped stream
   */
  protected DataOutput ensureDataOutput(OutputStream out) {
    if (out instanceof DataOutput) {
      return (DataOutput) out;
    } else {
      return new DataOutputStream(out);
    }
  }
  
  @SuppressWarnings("unchecked")
  @Override
  public Serialization<T> clone() {
    try {
      return (Serialization<T>) super.clone();
    } catch (CloneNotSupportedException e) {
      throw new IllegalArgumentException("Can't clone object " + this, e);
    }
  }
}