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    • com.davidbracewell.conversion.CollectionConverter Maven / Gradle / Ivy

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    /*
 * (c) 2005 David B. Bracewell
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.davidbracewell.conversion;

import com.davidbracewell.collection.Collect;
import com.davidbracewell.io.CSV;
import com.davidbracewell.io.structured.csv.CSVReader;
import com.davidbracewell.logging.Logger;
import com.google.common.base.Function;
import com.google.common.base.Throwables;

import java.io.IOException;
import java.io.StringReader;
import java.util.*;

/**
 * Converts objects to collections and iterables
 *
 * @author David B. Bracewell
 */
public final class CollectionConverter {

  /**
   * Converts an object to an iterable. Will only return null if the input is null
   */
  public static final Function> ITERABLE = new Function>() {
    
    @Override
    public Iterable apply( Object object) {
      if (object == null) {
        return Collections.emptyList();
      } else if (object instanceof Iterable) {
        return Cast.as(object);
      } else if (object instanceof Iterator) {
        return Collect.asIterable(Cast.>as(object));
      } else if (object instanceof Map) {
        return Cast.as(Cast.as(object).entrySet());
      } else if (object.getClass().isArray()) {
        return Cast.as(Collect.asIterable(object, Object.class));
      } else if (object instanceof CharSequence) {
        List list = new ArrayList<>();
        try (CSVReader reader = CSV.builder().removeEmptyCells().reader(new StringReader(object.toString()))) {
          List row;
          while ((row = reader.nextRow()) != null) {
            list.addAll(row);
          }
          return Cast.as(list);
        } catch (IOException e) {
          throw Throwables.propagate(e);
        }
      }

      return Cast.as(Collections.singletonList(object));
    }
  };

  private static final Logger log = Logger.getLogger(CollectionConverter.class);


  private CollectionConverter() {
  }

  /**
   * Converts an object to a collection
   *
   * @param collectionType the collection type
   * @return the conversion function
   */
  public static Function> COLLECTION(final Class collectionType) {
    return new Function>() {
      
      @Override
      public Collection apply( Object input) {
        if (input == null) {
          return null;
        } else if (collectionType == null) {
          return null;
        } else if (collectionType.isAssignableFrom(input.getClass())) {
          return Cast.as(input);
        }
        Iterable iterable = ITERABLE.apply(input);
        if (iterable != null) {
          Collection collection = Cast.as(Collect.create(collectionType));
          if (collection == null) {
            log.fine("Unable to create a collection of type {0}", collectionType);
            return null;
          }
          for (Object o : iterable) {
            collection.add(o);
          }
          return collection;
        }

        log.fine("Unable to convert {0} to a Collection of type {1}", input.getClass(), collectionType);
        return null;
      }
    };
  }


  /**
   * Converts an object to a collection and converts the components as well.
   *
   * @param             the component type parameter
   * @param collectionType the collection type
   * @param componentType  the component type
   * @return the conversion function
   */
  public static  Function> COLLECTION(final Class collectionType, final Class componentType) {
    return new Function>() {
      
      @Override
      public Collection apply( Object input) {
        if (input == null) {
          return null;
        } else if (collectionType == null) {
          log.fine("No collection type was given, returning null");
          return null;
        } else if (componentType == null) {
          log.fine("No component type was given, returning null");
          return null;
        }

        Iterable iterable = ITERABLE.apply(input);
        if (iterable != null) {
          Collection collection = Cast.as(Collect.create(collectionType));
          if (collection == null) {
            log.fine("Unable to create a collection of type {0}", collectionType);
            return null;
          }
          int added = 0;
          for (Object o : iterable) {
            T obj = Convert.convert(o, componentType);
            if (obj != null) {
              collection.add(obj);
              added++;
            }
          }
          if (added == 0) {
            log.fine("Unable to convert components to {0}", componentType);
            return null;
          }
          return collection;
        }

        log.fine("Unable to convert {0} to a Collection of type {1}", input.getClass(), collectionType);
        return null;
      }
    };
  }


}//END OF CollectionConverter
    
    
    
    

    




    
    
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