    001    /* $Id: LoaderFromClass.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.lang.reflect.Method;
    022
    023    import org.apache.commons.digester.Digester;
    024    import org.apache.commons.beanutils.MethodUtils;
    025    import org.apache.commons.logging.Log;
    026    import org.apache.commons.digester.plugins.RuleLoader;
    027    import org.apache.commons.digester.plugins.PluginException;
    028
    029    /**
    030     * A RuleLoader which invokes a static method on a target class, leaving that
    031     * method to actually instantiate and add new rules to a Digester instance.
    032     *
    033     * @since 1.6
    034     */
    035
    036    public class LoaderFromClass extends RuleLoader {
    037
    038        private Class<?> rulesClass;
    039        private Method rulesMethod;
    040
    041        /** Constructor. */
    042        public LoaderFromClass(Class<?> rulesClass, Method rulesMethod) {
    043            this.rulesClass = rulesClass;
    044            this.rulesMethod = rulesMethod;
    045        }
    046
    047        /** Constructor. */
    048        public LoaderFromClass(Class<?> rulesClass, String methodName)
    049                    throws PluginException {
    050
    051            Method method = locateMethod(rulesClass, methodName);
    052
    053            if (method == null) {
    054                throw new PluginException(
    055                    "rule class " + rulesClass.getName()
    056                    + " does not have method " + methodName
    057                    + " or that method has an invalid signature.");
    058            }
    059
    060            this.rulesClass = rulesClass;
    061            this.rulesMethod = method;
    062        }
    063
    064        /**
    065         * Just invoke the target method.
    066         */
    067        public void addRules(Digester d, String path) throws PluginException {
    068            Log log = d.getLogger();
    069            boolean debug = log.isDebugEnabled();
    070            if (debug) {
    071                log.debug(
    072                    "LoaderFromClass loading rules for plugin at path ["
    073                    + path + "]");
    074            }
    075
    076            try {
    077                Object[] params = {d, path};
    078                rulesMethod.invoke(null, params);
    079            } catch (Exception e) {
    080                throw new PluginException(
    081                    "Unable to invoke rules method " + rulesMethod
    082                    + " on rules class " + rulesClass, e);
    083            }
    084        }
    085
    086        /**
    087         * Find a method on the specified class whose name matches methodName,
    088         * and whose signature is:
    089         * <code> public static void foo(Digester d, String patternPrefix);</code>.
    090         *
    091         * @return null if no such method exists.
    092         */
    093        public static Method locateMethod(Class<?> rulesClass, String methodName)
    094                                throws PluginException {
    095
    096            Class<?>[] paramSpec = { Digester.class, String.class };
    097            Method rulesMethod = MethodUtils.getAccessibleMethod(
    098                rulesClass, methodName, paramSpec);
    099
    100            return rulesMethod;
    101        }
    102    }
    103