spring CollectionToArrayConverter 源码
spring CollectionToArrayConverter 代码
文件路径：/spring-core/src/main/java/org/springframework/core/convert/support/CollectionToArrayConverter.java
/*
* Copyright 2002-2017 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.core.convert.support;
import java.lang.reflect.Array;
import java.util.Collection;
import java.util.Collections;
import java.util.Set;
import org.springframework.core.convert.ConversionService;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.core.convert.converter.ConditionalGenericConverter;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
/**
* Converts a Collection to an array.
*
* <p>First, creates a new array of the requested targetType with a length equal to the
* size of the source Collection. Then sets each collection element into the array.
* Will perform an element conversion from the collection's parameterized type to the
* array's component type if necessary.
*
* @author Keith Donald
* @author Juergen Hoeller
* @since 3.0
*/
final class CollectionToArrayConverter implements ConditionalGenericConverter {
private final ConversionService conversionService;
public CollectionToArrayConverter(ConversionService conversionService) {
this.conversionService = conversionService;
}
@Override
public Set<ConvertiblePair> getConvertibleTypes() {
return Collections.singleton(new ConvertiblePair(Collection.class, Object[].class));
}
@Override
public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
return ConversionUtils.canConvertElements(sourceType.getElementTypeDescriptor(),
targetType.getElementTypeDescriptor(), this.conversionService);
}
@Override
@Nullable
public Object convert(@Nullable Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
if (source == null) {
return null;
}
Collection<?> sourceCollection = (Collection<?>) source;
TypeDescriptor targetElementType = targetType.getElementTypeDescriptor();
Assert.state(targetElementType != null, "No target element type");
Object array = Array.newInstance(targetElementType.getType(), sourceCollection.size());
int i = 0;
for (Object sourceElement : sourceCollection) {
Object targetElement = this.conversionService.convert(sourceElement,
sourceType.elementTypeDescriptor(sourceElement), targetElementType);
Array.set(array, i++, targetElement);
}
return array;
}
}
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