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SchemaCrawler is an open-source Java API that makes working with database metadata as easy as working with plain old Java objects. SchemaCrawler is also a database schema discovery and comprehension, and schema documentation tool. You can search for database schema objects using regular expressions, and output the schema and data in a readable text format. The output is designed to be diff-ed against other database schemas.

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/*
========================================================================
SchemaCrawler
http://www.schemacrawler.com
Copyright (c) 2000-2018, Sualeh Fatehi .
All rights reserved.
------------------------------------------------------------------------

SchemaCrawler is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

SchemaCrawler and the accompanying materials are made available under
the terms of the Eclipse Public License v1.0, GNU General Public License
v3 or GNU Lesser General Public License v3.

You may elect to redistribute this code under any of these licenses.

The Eclipse Public License is available at:
http://www.eclipse.org/legal/epl-v10.html

The GNU General Public License v3 and the GNU Lesser General Public
License v3 are available at:
http://www.gnu.org/licenses/

========================================================================
*/
package schemacrawler.crawl;


import static java.util.Objects.requireNonNull;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.lang.ref.Reference;
import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;

import schemacrawler.schema.DatabaseObject;
import schemacrawler.schema.PartialDatabaseObject;

class DatabaseObjectReference
  implements Serializable
{

  private static final long serialVersionUID = 1748828818899660921L;

  private Reference databaseObjectRef;
  private D partial;

  DatabaseObjectReference(final D databaseObject, final D partial)
  {
    databaseObjectRef = new SoftReference<>(requireNonNull(databaseObject,
                                                           "Database object not provided"));

    this.partial = requireNonNull(partial,
                                  "Partial database object not provided");
    if (!(partial instanceof PartialDatabaseObject))
    {
      throw new IllegalArgumentException("Partial database object not provided");
    }

    if (!partial.equals(databaseObject))
    {
      throw new IllegalArgumentException("Inconsistent database object reference");
    }
  }

  @Override
  public boolean equals(final Object obj)
  {
    return partial.equals(obj);
  }

  /**
   * {@inheritDoc} Modification over the Reference, always returns a
   * non-null value.
   *
   * @see java.lang.ref.SoftReference#get()
   */
  public D get()
  {
    final D dereferencedDatabaseObject;
    if (databaseObjectRef != null)
    {
      dereferencedDatabaseObject = databaseObjectRef.get();
    }
    else
    {
      dereferencedDatabaseObject = null;
    }

    if (dereferencedDatabaseObject == null)
    {
      return partial;
    }
    else
    {
      return dereferencedDatabaseObject;
    }
  }

  @Override
  public int hashCode()
  {
    return partial.hashCode();
  }

  public boolean isPartialDatabaseObjectReference()
  {
    return this.get() instanceof PartialDatabaseObject;
  }

  @Override
  public String toString()
  {
    return partial.toString();
  }

  /**
   * Read saved content of the reference, construct new reference, and
   * the partial.
   *
   * @param in
   * @throws IOException
   * @throws ClassNotFoundException
   */
  private void readObject(final ObjectInputStream in)
    throws IOException, ClassNotFoundException
  {
    if (in != null)
    {
      partial = (D) in.readObject();
      databaseObjectRef = new WeakReference(in.readObject());
    }
  }

  /**
   * Write only content of the reference. A Reference itself is not
   * serializable.
   *
   * @param out
   * @throws java.io.IOException
   */
  private void writeObject(final ObjectOutputStream out)
    throws IOException
  {
    if (out != null)
    {
      out.writeObject(partial);
      out.writeObject(databaseObjectRef.get());
    }
  }

}