JAVA 空值排序 ComparatorUtils

/**
 * ==============================================
 * Copy right 2015-2018 by ja
 * ----------------------------------------------
 * This is not a free software, without any authorization is not allowed to use and spread.
 * ==============================================
 *
 * @author : Jalan
 * @version : v1.0.0
 * @desc : 把对象属性抽象出来，可做为参数传递
 * @since : 2018/2/7 21:07
 */
@FunctionalInterface
public interface ObjectPropertyPredicate<T> {
    /**
     * 把属性当参数传递到方法中，由方法去处理这个属性的值做什么。
     * 传参使用: o -> o.propertyName
     * 接收参数方法内使用:
     *  参数：ObjectPropertyPredicate<FreeReportDataVO> express
     *  Predicate<Object> press = (obj) -> express.getProperty(obj).toString().startsWith("测试");
     *  express.getProperty(obj)
     * @param o
     * @return
     */
    Object getProperty(T o);
}

/**
 * ==============================================
 * Copy right 2015-2018 
 * ----------------------------------------------
 * This is not a free software, without any authorization is not allowed to use and spread.
 * ==============================================
 *
 * @author : Jalan
 * @version : v1.0.0
 * @desc : 含空值的排序工具 根据对象的某一属性值进行排序
 * @since : 2018/4/18 17:39
 */
public class ComparatorUtils {

    /**
     * 支持NULL排序 升序
     * 1、null 会排前面
     *
     * @param propertyPredicate 属性
     * @param <T>
     * @return
     */
    public static <T> Comparator<T> sort(ObjectPropertyPredicate<T> propertyPredicate) {
        Comparator<T> comparator = (obj1, obj2) -> {
            Object v1 = propertyPredicate.getProperty(obj1);
            Object v2 = propertyPredicate.getProperty(obj2);
            if (v1 == v2) {
                return 0;
            } else if (v1 == null) {
                return -1;
            } else if (v2 == null) {
                return 1;
            }
            if (v1 instanceof Integer) {
                return (Integer) v1 - (Integer) v2;
            } else if (v1 instanceof Date) {
                return ((Date) v1).compareTo((Date) v2);
            } else if (v1 instanceof BigDecimal) {
                return ((BigDecimal) v1).compareTo((BigDecimal) v2);
            }
            return v1.toString().compareTo(v2.toString());
        };
        return comparator;
    }

    /**
     * 支持NULL排序 降序
     * 1、null 会排后面
     *
     * @param propertyPredicate 属性
     * @param <T>
     * @return
     */
    public static <T> Comparator<T> sortDesc(ObjectPropertyPredicate<T> propertyPredicate) {
        Comparator<T> comparator = (obj1, obj2) -> {
            Object v1 = propertyPredicate.getProperty(obj1);
            Object v2 = propertyPredicate.getProperty(obj2);
            if (v1 == v2) {
                return 0;
            } else if (v1 == null) {
                return 1;
            } else if (v2 == null) {
                return -1;
            }
            if (v1 instanceof Integer) {
                return (Integer) v2 - (Integer) v1;
            } else if (v1 instanceof Date) {
                return ((Date) v2).compareTo((Date) v1);
            } else if (v1 instanceof BigDecimal) {
                return ((BigDecimal) v2).compareTo((BigDecimal) v1);
            }
            return v2.toString().compareTo(v1.toString());
        };
        return comparator;
    }
}