hierarchicalconfiguration.java

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/* ========================================================================
 * JCommon : a free general purpose class library for the Java(tm) platform
 * ========================================================================
 *
 * (C) Copyright 2000-2004, 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., 59 Temple Place, Suite 330,
 * Boston, MA 02111-1307, 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 1.4 2005/06/01 14:12:28 taqua 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;

/**
 * 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 {

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

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

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

    /**
     * Creates a new configuration.
     *
     * @param parentConfiguration the parent configuration.
     */
    public HierarchicalConfiguration(final ModifiableConfiguration 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 ModifiableConfiguration 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 ModifiableConfiguration 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 ModifiableConfiguration 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(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) {
            parentConfiguration = (ModifiableConfiguration) in.readObject();
        }
        else {
            parentConfiguration = null;
        }
        configurationLoaded();
    }

}