lodsve.core.utils.ListUtils Maven / Gradle / Ivy

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/*
 * Copyright (C) 2018  Sun.Hao
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */

package lodsve.core.utils;

import org.springframework.util.CollectionUtils;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * utils for list.
 *
 * @author sunhao([email protected])
 * @date 2015/8/17.
 */
public class ListUtils {

    /**
     * 根据key查询
     *
     * @param  key类型
     * @param  value类型
     */
    public interface KeyFinder {
        /**
         * 根据key查询
         *
         * @param target key
         * @return value
         */
        K findKey(T target);
    }

    /**
     * 判断是否符合条件
     *
     * @param  集合元素类型
     */
    public interface Decide {
        /**
         * 判断
         *
         * @param target 待判断对象
         * @return true/false
         */
        boolean judge(T target);
    }

    /**
     * 将一个对象集合转成另外一个对象的集合
     *
     * @param  原集合元素类型
     * @param  新集合元素类型
     */
    public interface Transform {
        /**
         * 单个元素转换
         *
         * @param target 原集合元素
         * @return 新集合元素
         */
        T transform(K target);
    }

    public static  Map toMap(Collection targets, KeyFinder keyFinder) {
        if (targets == null) {
            return Collections.emptyMap();
        }
        Map result = new HashMap<>(targets.size());
        for (T target : targets) {
            result.put(keyFinder.findKey(target), target);
        }
        return result;
    }

    public static  T findOne(Collection targets, Decide decide) {
        if (CollectionUtils.isEmpty(targets)) {
            return null;
        }

        for (T target : targets) {
            if (decide.judge(target)) {
                return target;
            }
        }

        return null;
    }

    public static  List findMore(Collection targets, Decide decide) {
        List result = new ArrayList<>();

        if (CollectionUtils.isEmpty(targets)) {
            return result;
        }

        for (T target : targets) {
            if (decide.judge(target)) {
                result.add(target);
            }
        }

        return result;
    }

    public static  List transform(Collection targets, Transform transform) {
        if (CollectionUtils.isEmpty(targets)) {
            return Collections.emptyList();
        }

        List result = new ArrayList<>(targets.size());
        for (K k : targets) {
            result.add(transform.transform(k));
        }

        return result;
    }
}