View Javadoc

    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  package org.apache.logging.log4j.core.config;
    18
    19  import java.util.Comparator;
    20
    21  import org.apache.logging.log4j.core.util.Assert;
    22
    23  /**
    24   * Comparator for classes annotated with {@link Order}.
    25   *
    26   * @since 2.1
    27   */
    28  public class OrderComparator implements Comparator<Class<?>> {
    29
    30      private static final Comparator<Class<?>> INSTANCE = new OrderComparator();
    31
    32      /**
    33       * Returns a singleton instance of this class.
    34       *
    35       * @return the singleton for this class.
    36       */
    37      public static Comparator<Class<?>> getInstance() {
    38          return INSTANCE;
    39      }
    40
    41      @Override
    42      public int compare(final Class<?> lhs, final Class<?> rhs) {
    43          final Order lhsOrder = Assert.requireNonNull(lhs, "lhs").getAnnotation(Order.class);
    44          final Order rhsOrder = Assert.requireNonNull(rhs, "rhs").getAnnotation(Order.class);
    45          if (lhsOrder == null && rhsOrder == null) {
    46              // both unannotated means equal priority
    47              return 0;
    48          }
    49          // if only one class is @Order-annotated, then prefer that one
    50          if (rhsOrder == null) {
    51              return -1;
    52          }
    53          if (lhsOrder == null) {
    54              return 1;
    55          }
    56          // larger value means lower priority
    57          return Integer.signum(rhsOrder.value() - lhsOrder.value());
    58      }
    59  }