001package org.apache.commons.digester3.plugins.strategies;
002
003/*
004 * Licensed to the Apache Software Foundation (ASF) under one
005 * or more contributor license agreements.  See the NOTICE file
006 * distributed with this work for additional information
007 * regarding copyright ownership.  The ASF licenses this file
008 * to you under the Apache License, Version 2.0 (the
009 * "License"); you may not use this file except in compliance
010 * with the License.  You may obtain a copy of the License at
011 *
012 *   http://www.apache.org/licenses/LICENSE-2.0
013 *
014 * Unless required by applicable law or agreed to in writing,
015 * software distributed under the License is distributed on an
016 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
017 * KIND, either express or implied.  See the License for the
018 * specific language governing permissions and limitations
019 * under the License.
020 */
021
022import java.util.Properties;
023
024import org.apache.commons.digester3.Digester;
025import org.apache.commons.digester3.plugins.PluginException;
026import org.apache.commons.digester3.plugins.RuleFinder;
027import org.apache.commons.digester3.plugins.RuleLoader;
028
029/**
030 * A rule-finding algorithm which expects the user to specify whether "automatic property setting" is desired. If this
031 * class discovers that this is in fact the case for a declaration, then a RuleLoader is returned which, when invoked,
032 * adds a single SetPropertiesRule instance to the digester.
033 * <p>
034 * This allows ordinary JavaBean classes to be used as plugins, and have xml attributes be mapped to bean properties of
035 * the same name, without any custom plugin rules being created for them.
036 * <p>
037 * This RuleFinder is typically used as the <i>last</i> RuleFinder, so that automatic property setting only occurs if
038 * there is no other source of custom rules available.
039 * 
040 * @since 1.6
041 */
042public class FinderSetProperties
043    extends RuleFinder
044{
045
046    private static final String DFLT_PROPS_ATTR = "setprops";
047
048    private static final String DFLT_FALSEVAL = "false";
049
050    private final String propsAttr;
051
052    private final String falseval;
053
054    /** See {@link #findLoader}. */
055    public FinderSetProperties()
056    {
057        this( DFLT_PROPS_ATTR, DFLT_FALSEVAL );
058    }
059
060    /**
061     * Create a rule-finder which will arrange for a SetPropertiesRule to be defined for each instance of a plugin, so
062     * that xml attributes map to bean properties.
063     * <p>
064     * Param falseval will commonly be the string "false" for config files written in English.
065     * 
066     * @param propsAttr must be non-null.
067     * @param falseval must be non-null.
068     */
069    public FinderSetProperties( String propsAttr, String falseval )
070    {
071        this.propsAttr = propsAttr;
072        this.falseval = falseval;
073    }
074
075    /**
076     * Returns a RuleLoader <i>unless</i> the properties contain an entry with the name matching constructor param
077     * propsAttr, and the value matching what is in falseval.
078     * <p>
079     * If no custom source of rules for a plugin is found, then the user almost always wants xml attributes to map to
080     * java bean properties, so this is the default behaviour unless the user explicitly indicates that they do
081     * <i>not</i> want a SetPropertiesRule to be provided for the plugged-in class.
082     * <p>
083     * The returned object (when non-null) will add a SetPropertiesRule to the digester whenever its addRules method is
084     * invoked.
085     *
086     * @param d The digester instance where locating plugin classes
087     * @param pluginClass The plugin Java class
088     * @param p The properties object that holds any xml attributes the user may have specified on the plugin
089     *          declaration in order to indicate how to locate the plugin rules.
090     * @return a source of digester rules for the specified plugin class.
091     * @throws PluginException if the algorithm finds a source of rules, but there is something invalid
092     *         about that source.
093     */
094    @Override
095    public RuleLoader findLoader( Digester d, Class<?> pluginClass, Properties p )
096        throws PluginException
097    {
098        String state = p.getProperty( propsAttr );
099        if ( ( state != null ) && state.equals( falseval ) )
100        {
101            // user has explicitly disabled automatic setting of properties.
102            // this is not expected to be common, but allowed.
103            return null;
104        }
105
106        return new LoaderSetProperties();
107    }
108
109}