Java 8特性

1.求和

items.stream().mapToLong(object::get).sum()

 2.字符集拆分为id

package cn.fw.finance.common.util;

import java.util.Collection;
import java.util.HashSet;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import static cn.fw.common.constant.CommonConstant.Symbol.COMMA;


public class StringUtils extends org.apache.commons.lang3.StringUtils {

    /**
     */
    public static Set<Long> convert2IdSet(String data) {
        return isBlank(data) ? new HashSet<>()
                : Stream.of(data.split(",")).map(Long::valueOf).collect(Collectors.toSet());
    }

    /**
     * 按逗号分割

     */
    public static Set<String> splitCommaToSet(String data) {
        return isBlank(data) ? new HashSet<>()
                : Stream.of(data.split(",")).collect(Collectors.toSet());
    }

    /**
     * id集合拼接为字符串
     *
     * @param data
     * @return
     */
    public static <T> String convert2CommaString(Collection<T> data) {
        return data.stream().map(String::valueOf).collect(Collectors.joining(","));
    }

}

3.分成集合

                .stream()
                .collect(Collectors.groupingBy(object::get, Collectors.mapping(object::get, Collectors.toList())));