001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements. See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License. You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    
018    package org.apache.logging.log4j.core.config.plugins.visitors;
019    
020    import java.lang.annotation.Annotation;
021    
022    import org.apache.logging.log4j.Logger;
023    import org.apache.logging.log4j.core.config.plugins.PluginVisitorStrategy;
024    import org.apache.logging.log4j.status.StatusLogger;
025    
026    /**
027     * Utility class to locate an appropriate {@link PluginVisitor} implementation for an annotation.
028     */
029    public final class PluginVisitors {
030    
031        private static final Logger LOGGER = StatusLogger.getLogger();
032    
033        private PluginVisitors() {
034        }
035    
036        /**
037         * Creates a PluginVisitor instance for the given annotation class using metadata provided by the annotation's
038         * {@link PluginVisitorStrategy} annotation. This instance must be further populated with
039         * data to be useful. Such data is passed through both the setters and the visit method.
040         *
041         * @param annotation the Plugin annotation class to find a PluginVisitor for.
042         * @return a PluginVisitor instance if one could be created, or {@code null} otherwise.
043         */
044        public static PluginVisitor<? extends Annotation> findVisitor(final Class<? extends Annotation> annotation) {
045            final PluginVisitorStrategy strategy = annotation.getAnnotation(PluginVisitorStrategy.class);
046            if (strategy == null) {
047                LOGGER.debug("No PluginVisitorStrategy found on annotation [{}]. Ignoring.", annotation);
048                return null;
049            }
050            try {
051                return strategy.value().newInstance();
052            } catch (final Exception e) {
053                LOGGER.error("Error loading PluginVisitor [{}] for annotation [{}].", strategy.value(), annotation, e);
054                return null;
055            }
056        }
057    }