    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    }