content: /*
   * Copyright 2012-2019 the original author or authors.
   *
   * 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
   *
   *      https://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 org.springframework.boot.convert;
  
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Set;
  import java.util.stream.Collectors;
  
  import org.springframework.core.convert.ConversionService;
  import org.springframework.core.convert.TypeDescriptor;
  import org.springframework.core.convert.converter.ConditionalGenericConverter;
  
  /**
   * Converts a Collection to a delimited String.
   *
   * @author Phillip Webb
   */
  final class CollectionToDelimitedStringConverter implements ConditionalGenericConverter {
  
  	private final ConversionService conversionService;
  
  	CollectionToDelimitedStringConverter(ConversionService conversionService) {
  		this.conversionService = conversionService;
  	}
  
  	@Override
  	public Set<ConvertiblePair> getConvertibleTypes() {
  		return Collections.singleton(new ConvertiblePair(Collection.class, String.class));
  	}
  
  	@Override
  	public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
  		TypeDescriptor sourceElementType = sourceType.getElementTypeDescriptor();
  		if (targetType == null || sourceElementType == null) {
  			return true;
  		}
  		return this.conversionService.canConvert(sourceElementType, targetType)
  				|| sourceElementType.getType().isAssignableFrom(targetType.getType());
  	}
  
  	@Override
  	public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
  		if (source == null) {
  			return null;
  		}
  		Collection<?> sourceCollection = (Collection<?>) source;
  		return convert(sourceCollection, sourceType, targetType);
  	}
  
  	private Object convert(Collection<?> source, TypeDescriptor sourceType, TypeDescriptor targetType) {
  		if (source.isEmpty()) {
  			return "";
  		}
  		return source.stream().map((element) -> convertElement(element, sourceType, targetType))
  				.collect(Collectors.joining(getDelimiter(sourceType)));
  	}
  
  	private CharSequence getDelimiter(TypeDescriptor sourceType) {
  		Delimiter annotation = sourceType.getAnnotation(Delimiter.class);
  		return (annotation != null) ? annotation.value() : ",";
  	}
  
  	private String convertElement(Object element, TypeDescriptor sourceType, TypeDescriptor targetType) {
  		return String.valueOf(
  				this.conversionService.convert(element, sourceType.elementTypeDescriptor(element), targetType));
  	}
  
  }
  