FlatConfigData.java
/*
* Copyright 2003-2004, Franz-Josef Elmer, All rights reserved
*
* 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 program 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
* (http://www.gnu.org/copyleft/lesser.html).
*
* 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
*/
package jcckit.util;
/**
* An implementation of <tt>ConfigData</tt> based on a flat
* representation of the hierachically organized key-value pairs.
* Concrete subclasses must implement the methods
* {@link #getValue} and {@link #createConfigData} in accordance
* with the Template Method pattern and Factory Method pattern,
* respectively.
* <p>
* In a flat representation of hierachically organized key-value
* pairs all key-value pairs are stored in a single <tt>Hashtable</tt>.
* Its key is the <em>full key</em> of the configuration data (i.e. the key
* including its path).
* <p>
* Example (using the notation for a <tt>.properties</tt> file):
* <pre>
* title = example
* symbolAttributes/className = jcckit.graphic.BasicDrawingAttributes
* symbolAttributes/fillColor = 0xcaffee
* symbolAttributes/lineColor = 0xff0000
* </pre>
* The following table shows the result of some method calls at a
* <tt>FlatConfigData</tt> instance prepared with
* this example:
* <p>
* <center>
* <table border=1 cellspacing=1 cellpadding=5>
* <tr><th>Method call</th><th>Result</th></tr>
* <tr><td>get("title")</td><td>example</td></tr>
* <tr><td>getNode("symbolAttributes").get("fillColor")
* </td><td>0xcaffee</td></tr>
* </table>
* </center>
* <p>
* In addition <tt>FlatConfigData</tt> implements <b>inheritance</b>
* of key-value pairs.
* Basically a node in the tree of key-value pairs
* may extend another node in the tree.
* The extended node inherit all key-value pairs from the extending
* one including the key-value pairs of all descendants.
* The value of a inherited key-value pair may be overridden.
* Also new key-value pairs may be placed in the inherited node or
* anywhere in the subtree.
* Note, that the extending node has to be a node which is not a
* descendant of the extended node (otherwise a circulary chain
* of references occurs). As a consequence not more than 20 inheritance
* levels are allowed.
* <p>
* The implementation of this kind of inheritance in a flat hashtable
* is done by an additional key-value pair of the form
* <pre>
* <i>extending-node</i><b>/</b> = <i>extended-node</i><b>/</b>
* </pre>
* Example:
* <pre>
* A/a/priority = high
* A/a/alpha/hello = universe
* A/a/alpha/answer = 42
* <b>A/b/1/ = A/a/</b>
* A/b/1/alpha/hello = world
* A/b/1/alpha/question = 6 * 7
* </pre>
* The following table shows the result of various method calls
* applied at the node <tt>A/b/1/</tt> of a <tt>FlatConfigData</tt>
* instance prepared with this example:
* <p>
* <center>
* <table border=1 cellspacing=1 cellpadding=5>
* <tr><th>Method call</th><th>Result</th><th>Comment</th></tr>
* <tr><td>get("priority")</td><td>high</td><td>inherited</td></tr>
* <tr><td>getNode("alpha").get("hello")
* </td><td>world</td><td>overridden</td></tr>
* <tr><td>getNode("alpha").get("question")
* </td><td>6 * 7</td><td>added</td></tr>
* <tr><td>getNode("alpha").get("answer")
* </td><td>42</td><td>inherited</td></tr>
* </table>
* </center>
*
* @author Franz-Josef Elmer
*/
public abstract class FlatConfigData implements ConfigData {
private final String _path;
/** Creates a new instance for the specified path. */
public FlatConfigData(String path) {
_path = path;
}
/**
* Returns the full key.
* @param key A (relative) key. <tt>null</tt> is not allowed.
* @return the path concatenated with <tt>key</tt> or <tt>key</tt>
* if the path is undefined.
*/
public String getFullKey(String key) {
return _path == null ? key : _path + key;
}
/**
* Returns the value associated with this key.
* @param key The relative key. <tt>null</tt> is not allowed.
* @return the associated value. Will be <tt>null</tt> if no value exists
* for <tt>key</tt>.
*/
public String get(String key) {
return get(_path, key, 0);
}
/**
* Obtains a value in accordance with hierarchy (<tt>path</tt>) and
* inheritance (recursive calls of this routine).
*/
private String get(String path, String key, int numberOfLevels) {
String result = null;
if (numberOfLevels < 20) {
String fullKey = path == null ? key : path + key;
result = getValue(fullKey);
if (result == null) {
// posAfterDelim is the index in path just after '/'
int posAfterDelim = path == null ? -1 : path.length();
String replacement;
while (posAfterDelim > 0) {
// look for a sub-tree
replacement = getValue(path.substring(0, posAfterDelim));
if (replacement != null) {
// sub-tree found, add last part of the original path
result = get(replacement + path.substring(posAfterDelim), key,
numberOfLevels + 1);
// break whether result is null or not.
break;
}
// remove last element from the path
posAfterDelim = path.lastIndexOf('/', posAfterDelim - 2) + 1;
}
}
}
return result;
}
/**
* Returns the <tt>ConfigData</tt> object associated with this key.
* @param key The relative key.
* @return the associated value. Will never return <tt>null</tt>.
* Instead an empty <tt>ConfigData</tt> is returned.
*/
public ConfigData getNode(String key) {
String path = (_path == null ? key : _path + key) + '/';
return createConfigData(path);
}
/**
* Returns the value for the specified full key from the flat
* representation of the hierarchically organized key-value pairs.
* @param fullKey The full key including path. <tt>null</tt> is not allowed.
* @return the value or <tt>null</tt> if not found.
*/
protected abstract String getValue(String fullKey);
/**
* Returns the <tt>FlatConfigData</tt> object for the specified full path.
* In general <tt>path</tt> will be used in the constructor with
* path argument.
* @param path The full path.
* @return a new instance in any case.
*/
protected abstract ConfigData createConfigData(String path);
}