001    /* $Id: FinderSetProperties.java 471661 2006-11-06 08:09:25Z skitching $
002     *
003     * Licensed to the Apache Software Foundation (ASF) under one or more
004     * contributor license agreements.  See the NOTICE file distributed with
005     * this work for additional information regarding copyright ownership.
006     * The ASF licenses this file to You under the Apache License, Version 2.0
007     * (the "License"); you may not use this file except in compliance with
008     * the License.  You may obtain a copy of the License at
009     * 
010     *      http://www.apache.org/licenses/LICENSE-2.0
011     * 
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */ 
018     
019    package org.apache.commons.digester.plugins.strategies;
020    
021    import java.util.Properties;
022    
023    import org.apache.commons.digester.Digester;
024    import org.apache.commons.digester.plugins.RuleFinder;
025    import org.apache.commons.digester.plugins.RuleLoader;
026    
027    /**
028     * A rule-finding algorithm which expects the user to specify whether
029     * "automatic property setting" is desired. If this class discovers that
030     * this is in fact the case for a declaration, then a RuleLoader is returned
031     * which, when invoked, adds a single SetPropertiesRule instance to the
032     * digester.
033     * <p>
034     * This allows ordinary JavaBean classes to be used as plugins, and have
035     * xml attributes be mapped to bean properties of the same name, without
036     * any custom plugin rules being created for them.
037     * <p>
038     * This RuleFinder is typically used as the <i>last</i> RuleFinder, so that
039     * automatic property setting only occurs if there is no other source of
040     * custom rules available.
041     *
042     * @since 1.6
043     */
044    
045    public class FinderSetProperties extends RuleFinder {
046        public static String DFLT_PROPS_ATTR = "setprops";
047        public static String DFLT_FALSEVAL = "false";
048    
049        private String propsAttr;
050        private String falseval;
051        
052        /** See {@link #findLoader}. */
053        public FinderSetProperties() {
054            this(DFLT_PROPS_ATTR, DFLT_FALSEVAL);
055        }
056        
057        /**
058         * Create a rule-finder which will arrange for a SetPropertiesRule to
059         * be defined for each instance of a plugin, so that xml attributes
060         * map to bean properties.
061         * <p>
062         * Param falseval will commonly be the string "false" for config files 
063         * written in English.
064         *
065         * @param propsAttr must be non-null.
066         * @param falseval must be non-null.
067         */
068        public FinderSetProperties(String propsAttr, String falseval) { 
069            this.propsAttr = propsAttr;
070            this.falseval = falseval;
071        }
072        
073        /**
074         * Returns a RuleLoader <i>unless</i> the properties contain an entry
075         * with the name matching constructor param propsAttr, and the value 
076         * matching what is in falseval.
077         * <p>
078         * If no custom source of rules for a plugin is found, then the user
079         * almost always wants xml attributes to map to java bean properties,
080         * so this is the default behaviour unless the user explicitly indicates
081         * that they do <i>not</i> want a SetPropertiesRule to be provided for
082         * the plugged-in class.
083         * <p>
084         * The returned object (when non-null) will add a SetPropertiesRule to
085         * the digester whenever its addRules method is invoked.
086         */
087        public RuleLoader findLoader(Digester d, Class pluginClass, Properties p) {
088            String state = p.getProperty(propsAttr);
089            if ((state != null)  && state.equals(falseval)) {
090                // user has explicitly disabled automatic setting of properties.
091                // this is not expected to be common, but allowed.
092                return null;
093            }
094            
095            return new LoaderSetProperties();
096        }
097    }
098