    001    /* $Id: FinderFromMethod.java 729125 2008-12-23 21:21:07Z rahul $
    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    import org.apache.commons.digester.Digester;
    023    import org.apache.commons.digester.plugins.RuleFinder;
    024    import org.apache.commons.digester.plugins.RuleLoader;
    025    import org.apache.commons.digester.plugins.PluginException;
    026
    027    /**
    028     * A rule-finding algorithm which expects the caller to specify a methodname
    029     * as a plugin property, where the method exists on the plugin class.
    030     *
    031     * @since 1.6
    032     */
    033
    034    public class FinderFromMethod extends RuleFinder {
    035        /**
    036         * Xml attribute that needs to be present on a plugin declaration
    037         * in order to specify the method to load rules from.
    038         */
    039        public static String DFLT_METHOD_ATTR = "method";
    040
    041        /** See {@link #findLoader}. */
    042        private String methodAttr;
    043
    044        /** Constructor. */
    045        public FinderFromMethod() {
    046            this(DFLT_METHOD_ATTR);
    047        }
    048
    049        /** See {@link #findLoader}. */
    050        public FinderFromMethod(String methodAttr) {
    051            this.methodAttr = methodAttr;
    052        }
    053
    054        /**
    055         * If there exists a property with the name matching constructor param
    056         * methodAttr, then locate the appropriate Method on the plugin class
    057         * and return an object encapsulating that info.
    058         * <p>
    059         * If there is no matching property provided, then just return null.
    060         * <p>
    061         * The returned object (when non-null) will invoke the target method
    062         * on the plugin class whenever its addRules method is invoked. The
    063         * target method is expected to have the following prototype:
    064         * <code> public static void xxxxx(Digester d, String patternPrefix); </code>
    065         */
    066        public RuleLoader findLoader(Digester d, Class<?> pluginClass, Properties p)
    067                            throws PluginException {
    068
    069            String methodName = p.getProperty(methodAttr);
    070            if (methodName == null) {
    071                // nope, user hasn't requested dynamic rules to be loaded
    072                // from a specific class.
    073                return null;
    074            }
    075
    076            return new LoaderFromClass(pluginClass, methodName);
    077        }
    078    }
    079