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    1   /*
    2    * Licensed to the Apache Software Foundation (ASF) under one or more
    3    * contributor license agreements. See the NOTICE file distributed with
    4    * this work for additional information regarding copyright ownership.
    5    * The ASF licenses this file to You under the Apache License, Version 2.0
    6    * (the "License"); you may not use this file except in compliance with
    7    * the License. You may obtain a copy of the License at
    8    *
    9    *      http://www.apache.org/licenses/LICENSE-2.0
    10   *
    11   * Unless required by applicable law or agreed to in writing, software
    12   * distributed under the License is distributed on an "AS IS" BASIS,
    13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    14   * See the License for the specific language governing permissions and
    15   * limitations under the License.
    16   */
    17
    18  package org.apache.logging.log4j.core.config.plugins.visitors;
    19
    20  import java.lang.annotation.Annotation;
    21
    22  import org.apache.logging.log4j.Logger;
    23  import org.apache.logging.log4j.core.config.plugins.PluginVisitorStrategy;
    24  import org.apache.logging.log4j.status.StatusLogger;
    25
    26  /**
    27   * Utility class to locate an appropriate {@link PluginVisitor} implementation for an annotation.
    28   */
    29  public final class PluginVisitors {
    30
    31      private static final Logger LOGGER = StatusLogger.getLogger();
    32
    33      private PluginVisitors() {
    34      }
    35
    36      /**
    37       * Creates a PluginVisitor instance for the given annotation class using metadata provided by the annotation's
    38       * {@link PluginVisitorStrategy} annotation. This instance must be further populated with
    39       * data to be useful. Such data is passed through both the setters and the visit method.
    40       *
    41       * @param annotation the Plugin annotation class to find a PluginVisitor for.
    42       * @return a PluginVisitor instance if one could be created, or {@code null} otherwise.
    43       */
    44      public static PluginVisitor<? extends Annotation> findVisitor(final Class<? extends Annotation> annotation) {
    45          final PluginVisitorStrategy strategy = annotation.getAnnotation(PluginVisitorStrategy.class);
    46          if (strategy == null) {
    47              LOGGER.debug("No PluginVisitorStrategy found on annotation [{}]. Ignoring.", annotation);
    48              return null;
    49          }
    50          try {
    51              return strategy.value().newInstance();
    52          } catch (final Exception e) {
    53              LOGGER.error("Error loading PluginVisitor [{}] for annotation [{}].", strategy.value(), annotation, e);
    54              return null;
    55          }
    56      }
    57  }