Java8 LocalDateTime周末过滤器

Question

我想编写一个布尔值函数，如果给定的LocalDateTime在时间上介于两个特定点之间，则返回true，否则为false。

具体来说，如果给定的日期在格林尼治时间星期五22:00和格林尼治时间周日23:00之间，我想要一个LocalDateTime过滤器。

一具骨架看起来可能是这样的：

public boolean isWeekend(LocalDateTime dateTime) {
    //Checks if dateTime falls in between Friday's 22:00 GMT and Sunday's 23:00 GMT
    //return ...???
}

这基本上是一个周末过滤器，我想知道是否有一个简单的解决方案与新的Java 8时代库(或任何其他现有的过滤器方法)。

我知道如何检查一周中的一天，小时等，但避免重新发明车轮。

Answer 1

为了实现这一点，我编写了一个小程序。

程序

public class TestWeekend {
    private static final int FRIDAY = 5;
    private static final int SATURDAY = 6;
    private static final int SUNDAY = 7;
    private static final Integer WEEKEND_START_FRIDAY_CUT_OFF_HOUR = 22;
    private static final Integer WEEKEND_END_SUNDAY_CUT_OFF_HOUR = 23;
    private static List<Integer> weekendDaysList = Arrays.asList(FRIDAY, SATURDAY, SUNDAY);

    public static void main(String []args) throws FileNotFoundException {
        System.out.println(" is weekend - "+isWeekend(LocalDateTime.of(2016,4,22,18,39)));
        System.out.println(" is weekend - "+isWeekend(LocalDateTime.of(2016,4,22,21,59)));
        System.out.println(" is weekend - "+isWeekend(LocalDateTime.of(2016,4,22,22,0)));
        System.out.println(" is weekend - "+isWeekend(LocalDateTime.of(2016,4,23,5,0)));
        System.out.println(" is weekend - "+isWeekend(LocalDateTime.of(2016,4,24,8,0)));
        System.out.println(" is weekend - "+isWeekend(LocalDateTime.of(2016,4,24,22,59)));
        System.out.println(" is weekend - "+isWeekend(LocalDateTime.of(2016,4,24,23,0)));
        System.out.println(" is weekend - "+isWeekend(LocalDateTime.of(2016,4,25,11,5)));
    }

    public static  boolean isWeekend(LocalDateTime dateTime) {
        System.out.print("Date - "+dateTime+" , ");
        if(weekendDaysList.contains(dateTime.getDayOfWeek().getValue()) ){
            if(SATURDAY ==  dateTime.getDayOfWeek().getValue()){
                return true;
            }
            if(FRIDAY == dateTime.getDayOfWeek().getValue() && dateTime.getHour() >=WEEKEND_START_FRIDAY_CUT_OFF_HOUR){
               return true;
            }else if(SUNDAY == dateTime.getDayOfWeek().getValue() && dateTime.getHour()  < WEEKEND_END_SUNDAY_CUT_OFF_HOUR ){
                return   true;
            }
        }
        //Checks if dateTime falls in between Friday's 22:00 GMT and Sunday's 23:00 GMT
         return false;
    }

 }

Answer 2

你认为这样的图书馆会怎样运作呢？当你的周末开始和结束的时候，你仍然需要告诉它，它最终不会比简单的短得多。

boolean isWeekend(LocalDateTime dt) {
    switch(dt.getDayOfWeek()) {
        case FRIDAY:
            return dt.getHour() >= ...;
        case SATURDAY:
            return true;
        case SUNDAY:
            return dt.getHour() < ...;
        default:
            return false;
    }
}

Answer 3

一个简单的TemporalQuery就可以做到这一点：

static class IsWeekendQuery implements TemporalQuery<Boolean>{

    @Override
    public Boolean queryFrom(TemporalAccessor temporal) {
        return temporal.get(ChronoField.DAY_OF_WEEK) >= 5;
    }
}

它将被调用如下(使用.now()获取要测试的值)：

boolean isItWeekendNow = LocalDateTime.now().query(new IsWeekendQuery());

或者，特别是在UTC时间(使用.now()获取要测试的值)：

boolean isItWeekendNow = OffsetDateTime.now(ZoneOffset.UTC).query(new IsWeekendQuery());

除了您的问题之外，每次使用IsWeekendQuery都没有理由创建一个新的实例，因此您可能希望创建一个静态的最终TemporalQuery，它将逻辑封装在lambda表达式中：

static final TemporalQuery<Boolean> IS_WEEKEND_QUERY = 
    t -> t.get(ChronoField.DAY_OF_WEEK) >= 5;

boolean isItWeekendNow = OffsetDateTime.now(ZoneOffset.UTC).query(IS_WEEKEND_QUERY);