List＜Map＞集合如何使用Stream流进行排序

流进行排序"/>

List＜Map＞集合如何使用Stream流进行排序

起因：最近在工作中遇到一个问题，我从数据库中查询数据，返回的数据是一个List

1、我要查询根据月份查询数据，这是我的最开始返回的结果，可以看见第12月排在第一条了，我理想的数据是从1月开始。

[{"lastYear": [{"monthtime": "12","operationtime": 11033},{"monthtime": "01","operationtime": 0},{"monthtime": "02","operationtime": 0},{"monthtime": "03","operationtime": 0},{"monthtime": "04","operationtime": 0},{"monthtime": "05","operationtime": 0},{"monthtime": "06","operationtime": 0},{"monthtime": "07","operationtime": 0},{"monthtime": "08","operationtime": 0},{"monthtime": "09","operationtime": 0},{"monthtime": "10","operationtime": 0},{"monthtime": "11","operationtime": 0},]}
]

然后我就想着对该数据进行排序处理。因为流排序的效率非常高。
**

这是我自己编写的排序代码：

**

list.stream().sorted(Comparatorparing(map -> Integer.parseInt(map.get("monthtime").toString()))).collect(Collectors.toList());

看一下Comparatorparing的源码：

 * @param  <T> the type of element to be compared* @param  <U> the type of the {@code Comparable} sort key* @param  keyExtractor the function used to extract the {@link*         Comparable} sort key* @return a comparator that compares by an extracted key* @throws NullPointerException if the argument is null* @since 1.8*/
public static <T, U extends Comparable<? super U>> Comparator<T> comparing(Function<? super T, ? extends U> keyExtractor)
{Objects.requireNonNull(keyExtractor);return (Comparator<T> & Serializable)(c1, c2) -> keyExtractor.apply(c1)pareTo(keyExtractor.apply(c2));
}

这个是函数式编程的特点，参数是一个方法，利用这个方法我们可以告诉排序方法我们需要根据什么来进行排序。我这里需要根据monthtime键对应的值进行排序，利用lambda表达式，把该函数传入即可。

排序后的结果：

[{"lastYear": [{"monthtime": "01","operationtime": 0},{"monthtime": "02","operationtime": 0},{"monthtime": "03","operationtime": 0},{"monthtime": "04","operationtime": 0},{"monthtime": "05","operationtime": 0},{"monthtime": "06","operationtime": 0},{"monthtime": "07","operationtime": 0},{"monthtime": "08","operationtime": 0},{"monthtime": "09","operationtime": 0},{"monthtime": "10","operationtime": 0},{"monthtime": "11","operationtime": 0},{"monthtime": "12","operationtime": 11033}]}
]

如有问题，请指正，谢谢！