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'rapiddweller Common' is an open source Java library forked from Databene Commons by Volker Bergmann. It provides extensions to the Java core library by utility classes, abstract concepts and concrete implementations.

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/*
 * Copyright (C) 2004-2015 Volker Bergmann ([email protected]).
 * All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.rapiddweller.common.comparator;

import com.rapiddweller.common.BeanUtil;
import com.rapiddweller.common.ComparableComparator;
import com.rapiddweller.common.ConfigurationError;
import com.rapiddweller.common.IOUtil;
import com.rapiddweller.common.NullSafeComparator;
import com.rapiddweller.common.StringUtil;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

import java.io.BufferedReader;
import java.io.IOException;
import java.lang.reflect.Type;
import java.text.Collator;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Map;

/**
 * Creates comparators by the type of the objects to be compared.
 * Created: 22.10.2005 21:29:08
 *
 * @author Volker Bergmann
 */
@SuppressWarnings({"unchecked", "rawtypes"})
public class ComparatorFactory {

  private static final Logger logger = LogManager.getLogger(ComparatorFactory.class);
  private static final String CONFIG_FILE_URI = "com/rapiddweller/common/comparator/comparators.txt";

  private static final Map, Comparator> comparators;

  static {
    comparators = new HashMap<>();
    addComparator(String.class, Collator.getInstance());
    readConfigFileIfExists();

    // this is the fallback if no specific Comparator was found
    addComparator(Comparable.class, new ComparableComparator());
  }

  /**
   * Add comparator.
   *
   * @param comparedClass the compared class
   * @param comparator    the comparator
   */
  public static void addComparator(Class comparedClass, Comparator comparator) {
    comparators.put(comparedClass, comparator);
  }

  private static void readConfigFileIfExists() {
    if (!IOUtil.isURIAvailable(ComparatorFactory.CONFIG_FILE_URI)) {
      logger.info("No custom Comparator setup defined, (" + ComparatorFactory.CONFIG_FILE_URI + "), using defaults");
      return;
    }
    BufferedReader reader = null;
    try {
      reader = IOUtil.getReaderForURI(ComparatorFactory.CONFIG_FILE_URI);
      String line;
      while ((line = reader.readLine()) != null) {
        line = line.trim();
        if (!StringUtil.isEmpty(line)) {
          createComparator(line);
        }
      }
    } catch (IOException e) {
      throw new ConfigurationError(e);
    } finally {
      IOUtil.close(reader);
    }
  }

  private static  void createComparator(String className) {
    Class> cls = BeanUtil.forName(className);
    Comparator comparator = BeanUtil.newInstance(cls);
    Type[] genTypes = BeanUtil.getGenericInterfaceParams(cls, Comparator.class);
    addComparator((Class) genTypes[0], comparator);
  }

  /**
   * Gets comparator.
   *
   * @param   the type parameter
   * @param type the type
   * @return the comparator
   */
  public static  Comparator getComparator(Class type) {
    Comparator comparator = (Comparator) comparators.get(type);
    if (comparator == null && Comparable.class.isAssignableFrom(type)) {
      comparator = new ComparableComparator();
    }
    if (comparator == null) {
      throw new RuntimeException("No Comparator defined for " + type.getName());
    }
    return new NullSafeComparator<>(comparator);
  }
}