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Hutool是一个小而全的Java工具类库，通过静态方法封装，降低相关API的学习成本，提高工作效率，使Java拥有函数式语言般的优雅，让Java语言也可以“甜甜的”。

There is a newer version: 5.8.34

package cn.hutool.core.convert.impl;

import cn.hutool.core.collection.CollUtil;
import cn.hutool.core.convert.Converter;
import cn.hutool.core.util.ObjectUtil;
import cn.hutool.core.util.TypeUtil;

import java.lang.reflect.Type;
import java.util.Collection;

/**
 * 各种集合类转换器
 *
 * @author Looly
 * @since 3.0.8
 */
public class CollectionConverter implements Converter> {

	/** 集合类型 */
	private final Type collectionType;
	/** 集合元素类型 */
	private final Type elementType;

	/**
	 * 构造，默认集合类型使用{@link Collection}
	 */
	public CollectionConverter() {
		this(Collection.class);
	}

	// ---------------------------------------------------------------------------------------------- Constractor start
	/**
	 * 构造
	 *
	 * @param collectionType 集合类型
	 */
	public CollectionConverter(Type collectionType) {
		this(collectionType, TypeUtil.getTypeArgument(collectionType));
	}

	/**
	 * 构造
	 *
	 * @param collectionType 集合类型
	 */
	public CollectionConverter(Class collectionType) {
		this(collectionType, TypeUtil.getTypeArgument(collectionType));
	}

	/**
	 * 构造
	 *
	 * @param collectionType 集合类型
	 * @param elementType 集合元素类型
	 */
	public CollectionConverter(Type collectionType, Type elementType) {
		this.collectionType = collectionType;
		this.elementType = elementType;
	}
	// ---------------------------------------------------------------------------------------------- Constractor end

	@Override
	public Collection convert(Object value, Collection defaultValue) throws IllegalArgumentException {
		final Collection result = convertInternal(value);
		return ObjectUtil.defaultIfNull(result, defaultValue);
	}

	/**
	 * 内部转换
	 *
	 * @param value 值
	 * @return 转换后的集合对象
	 */
	protected Collection convertInternal(Object value) {
		final Collection collection = CollUtil.create(TypeUtil.getClass(this.collectionType), TypeUtil.getClass(this.elementType));
		return CollUtil.addAll(collection, value, this.elementType);
	}
}