hierarchicalconfiguration.java

JCommon is a Java class library that is used by JFreeChart, Pentaho Reporting and a few other projec

/* ========================================================================
 * JCommon : a free general purpose class library for the Java(tm) platform
 * ========================================================================
 *
 * (C) Copyright 2000-2005, by Object Refinery Limited and Contributors.
 *
 * Project Info:  http://www.jfree.org/jcommon/index.html
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library 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. See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
 * USA.
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
 * in the United States and other countries.]
 *
 * ------------------------------
 * HierarchicalConfiguration.java
 * ------------------------------
 * (C) Copyright 2004, by Object Refinery Limited.
 *
 * Original Author:  Thomas Morgner;
 * Contributor(s):   David Gilbert (for Object Refinery Limited);
 *
 * $Id: HierarchicalConfiguration.java,v 1.8 2008/09/10 09:17:28 mungady Exp $
 *
 * Changes
 * -------
 * 07-Jun-2004 : Added JCommon header (DG);
 * 29-Jul-2004 : Replaced 'enum' variable name (reserved word in JDK 1.5) (DG);
 *
 */

package org.jfree.base.config;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.Properties;
import java.util.TreeSet;

import org.jfree.util.Configuration;
import org.jfree.util.PublicCloneable;

/**
 * A hierarchical configuration. Such a configuration can have one or more
 * parent configurations providing usefull default values.
 *
 * @author Thomas Morgner
 */
public class HierarchicalConfiguration
    implements ModifiableConfiguration, PublicCloneable
{

  /**
   * The instance configuration properties.
   */
  private Properties configuration;

  /**
   * The parent configuration (null if this is the root configuration).
   */
  private transient Configuration parentConfiguration;

  /**
   * Creates a new configuration.
   */
  public HierarchicalConfiguration()
  {
    this.configuration = new Properties();
  }

  /**
   * Creates a new configuration.
   *
   * @param parentConfiguration the parent configuration.
   */
  public HierarchicalConfiguration(final Configuration parentConfiguration)
  {
    this();
    this.parentConfiguration = parentConfiguration;
  }

  /**
   * Returns the configuration property with the specified key.
   *
   * @param key the property key.
   * @return the property value.
   */
  public String getConfigProperty(final String key)
  {
    return getConfigProperty(key, null);
  }

  /**
   * Returns the configuration property with the specified key (or the
   * specified default value if there is no such property).
   * <p/>
   * If the property is not defined in this configuration, the code will
   * lookup the property in the parent configuration.
   *
   * @param key          the property key.
   * @param defaultValue the default value.
   * @return the property value.
   */
  public String getConfigProperty(final String key, final String defaultValue)
  {
    String value = this.configuration.getProperty(key);
    if (value == null)
    {
      if (isRootConfig())
      {
        value = defaultValue;
      }
      else
      {
        value = this.parentConfiguration.getConfigProperty(key, defaultValue);
      }
    }
    return value;
  }

  /**
   * Sets a configuration property.
   *
   * @param key   the property key.
   * @param value the property value.
   */
  public void setConfigProperty(final String key, final String value)
  {
    if (key == null)
    {
      throw new NullPointerException();
    }

    if (value == null)
    {
      this.configuration.remove(key);
    }
    else
    {
      this.configuration.setProperty(key, value);
    }
  }

  /**
   * Returns true if this object has no parent.
   *
   * @return true, if this report is the root configuration, false otherwise.
   */
  private boolean isRootConfig()
  {
    return this.parentConfiguration == null;
  }

  /**
   * Checks, whether the given key is localy defined in this instance or
   * whether the key's value is inherited.
   *
   * @param key the key that should be checked.
   * @return true, if the key is defined locally, false otherwise.
   */
  public boolean isLocallyDefined(final String key)
  {
    return this.configuration.containsKey(key);
  }

  /**
   * Returns the collection of properties for the configuration.
   *
   * @return the properties.
   */
  protected Properties getConfiguration()
  {
    return this.configuration;
  }

  /**
   * The new configuartion will be inserted into the list of report
   * configuration, so that this configuration has the given report
   * configuration instance as parent.
   *
   * @param config the new report configuration.
   */
  public void insertConfiguration(final HierarchicalConfiguration config)
  {
    config.setParentConfig(getParentConfig());
    setParentConfig(config);
  }

  /**
   * Set the parent configuration. The parent configuration is queried, if the
   * requested configuration values was not found in this report
   * configuration.
   *
   * @param config the parent configuration.
   */
  protected void setParentConfig(final Configuration config)
  {
    if (this.parentConfiguration == this)
    {
      throw new IllegalArgumentException("Cannot add myself as parent configuration.");
    }
    this.parentConfiguration = config;
  }

  /**
   * Returns the parent configuration. The parent configuration is queried, if
   * the requested configuration values was not found in this report
   * configuration.
   *
   * @return the parent configuration.
   */
  protected Configuration getParentConfig()
  {
    return this.parentConfiguration;
  }

  /**
   * Returns all defined configuration properties for the report. The
   * enumeration contains all keys of the changed properties, properties set
   * from files or the system properties are not included.
   *
   * @return all defined configuration properties for the report.
   */
  public Enumeration getConfigProperties()
  {
    return this.configuration.keys();
  }

  /**
   * Searches all property keys that start with a given prefix.
   *
   * @param prefix the prefix that all selected property keys should share
   * @return the properties as iterator.
   */
  public Iterator findPropertyKeys(final String prefix)
  {
    final TreeSet keys = new TreeSet();
    collectPropertyKeys(prefix, this, keys);
    return Collections.unmodifiableSet(keys).iterator();
  }

  /**
   * Collects property keys from this and all parent report configurations,
   * which start with the given prefix.
   *
   * @param prefix    the prefix, that selects the property keys.
   * @param config    the currently processed report configuration.
   * @param collector the target list, that should receive all valid keys.
   */
  private void collectPropertyKeys(final String prefix,
                                   final Configuration config,
                                   final TreeSet collector)
  {
    final Enumeration enum1 = config.getConfigProperties();
    while (enum1.hasMoreElements())
    {
      final String key = (String) enum1.nextElement();
      if (key.startsWith(prefix))
      {
        if (collector.contains(key) == false)
        {
          collector.add(key);
        }
      }
    }

    if (config instanceof HierarchicalConfiguration)
    {
      final HierarchicalConfiguration hconfig = (HierarchicalConfiguration) config;
      if (hconfig.parentConfiguration != null)
      {
        collectPropertyKeys(prefix, hconfig.parentConfiguration, collector);
      }
    }
  }

  /**
   * Checks, whether the parent configuration can be serialized. Usually the
   * global configuration is not serialized and should return false here.
   *
   * @return true, if the parent config can be serialized, false otherwise.
   */
  protected boolean isParentSaved()
  {
    return true;
  }

  /**
   * A callback method to reconnect this configuration with the global
   * configuration after deserialization.
   */
  protected void configurationLoaded()
  {
  }

  /**
   * Helper method for serialization.
   *
   * @param out the output stream where to write the object.
   * @throws java.io.IOException if errors occur while writing the stream.
   */
  private void writeObject(final ObjectOutputStream out)
      throws IOException
  {
    out.defaultWriteObject();
    if (isParentSaved() == false)
    {
      out.writeBoolean(false);
    }
    else
    {
      out.writeBoolean(true);
      out.writeObject(this.parentConfiguration);
    }
  }

  /**
   * Helper method for serialization.
   *
   * @param in the input stream from where to read the serialized object.
   * @throws IOException            when reading the stream fails.
   * @throws ClassNotFoundException if a class definition for a serialized
   *                                object could not be found.
   */
  private void readObject(final ObjectInputStream in)
      throws IOException, ClassNotFoundException
  {
    in.defaultReadObject();
    final boolean readParent = in.readBoolean();
    if (readParent)
    {
        this.parentConfiguration = (ModifiableConfiguration) in.readObject();
    }
    else
    {
        this.parentConfiguration = null;
    }
    configurationLoaded();
  }

  /**
   * Returns a clone of this instance.
   *
   * @return A clone.
   *
   * @throws CloneNotSupportedException if there is a problem cloning.
   */
  public Object clone() throws CloneNotSupportedException
  {
    HierarchicalConfiguration config = (HierarchicalConfiguration) super.clone();
    config.configuration = (Properties) this.configuration.clone();
    return config;
  }
}