12.2 操纵、解析和格式化日期

直接修改

LocalDate date1 = LocalDate.of(2014, 3, 18); // 2014-03-18
LocalDate date2 = date1.withYear(2011); // 2011-03-18
LocalDate date3 = date2.withDayOfMonth(25); // 2011-03-25
LocalDate date4 = date3.with(ChronoField.MONTH_OF_YEAR, 9); // 2011-09-25

间接修改

LocalDate date1 = LocalDate.of(2014, 3, 18); // 2014-03-18
LocalDate date2 = date1.minusYears(3); // 2011-03-18
LocalDate date3 = date2.plusWeeks(1); // 2011-03-25
LocalDate date4 = date3.plus(6, ChronoUnit.MONTHS); // 2011-09-25

测验12.1操纵LocalDate对象
经过下面这些操作，date变量的值是什么？

LocalDate date = LocalDate.of(2014, 3, 18); // 2014-03-18
date = date.with(ChronoField.MONTH_OF_YEAR, 9); // 2014-09-18
date = date.plusYears(2).minusDays(10); // 2016-09-08
date.withYear(2011); // 2011-09-08
System.out.println(date); // 2016-09-08

注意：最后一次date.withYear(2011);修改后未赋值，因此结果是2016-09-08。

12.2.1 使用TemporalAdjuster

更复杂的日期操作，例如，将日期调整到下个周日、下个工作日，或者是本月的最后一天。

基于java.time.temporal.Temporal#with(TemporalAdjuster adjuster)实现日期的调整。

java.time.temporal.TemporalAdjusters的静态方法中提供了大量预定义的TemporalAdjuster。

TemporalAdjuster将一个Temporal对象转换为一个Temporal对象并返回

@FunctionalInterface
public interface TemporalAdjuster {
    Temporal adjustInto(Temporal temporal);
}

测验12.2 实现一个定制的TemporalAdjuster

请设计一个NextWorkingDay类，该类实现了TemporalAdjuster接口，能够计算下一个工作日（不考虑法定年节假日）。

如果当天的星期介于周一至周五之间，日期向后移动一天；如果当天是周六或者周日，则返回下一个周一。

class NextWorkingDay implements TemporalAdjuster {
    @Override
    public Temporal adjustInto(Temporal temporal) {
        if (Objects.isNull(temporal)) {
            return null;
        }
        DayOfWeek dayOfWeek = DayOfWeek.of(temporal.get(ChronoField.DAY_OF_WEEK));
        int dayToAdd = 1;
        if (dayOfWeek == DayOfWeek.FRIDAY) {
            dayToAdd = 3;
        } else if (dayOfWeek == DayOfWeek.SATURDAY) {
            dayToAdd = 2;
        }
        return temporal.plus(dayToAdd, ChronoUnit.DAYS);
    }
}

使用

1. 基于对象：date.with(new NextWorkingDay())；

2. 基于lambda表达式；

   date.with(temporal -> {
       if (Objects.isNull(temporal)) {
           return null;
       }
       DayOfWeek dayOfWeek = DayOfWeek.of(temporal.get(ChronoField.DAY_OF_WEEK));
       int dayToAdd = 1;
       if (dayOfWeek == DayOfWeek.FRIDAY) {
           dayToAdd = 3;
       } else if (dayOfWeek == DayOfWeek.SATURDAY) {
           dayToAdd = 2;
       }
       return temporal.plus(dayToAdd, ChronoUnit.DAYS);
   });
   

3. 基于静态工厂方法TemporalAdjuster#ofDateAdjuster生成TemporalAdjuster；

   TemporalAdjuster temporalAdjuster = TemporalAdjusters.ofDateAdjuster(temporal -> {
       if (Objects.isNull(temporal)) {
           return null;
       }
       DayOfWeek dayOfWeek = DayOfWeek.of(temporal.get(ChronoField.DAY_OF_WEEK));
       int dayToAdd = 1;
       if (dayOfWeek == DayOfWeek.FRIDAY) {
           dayToAdd = 3;
       } else if (dayOfWeek == DayOfWeek.SATURDAY) {
           dayToAdd = 2;
       }
       return temporal.plus(dayToAdd, ChronoUnit.DAYS);
   });
   
   date.with(temporalAdjuster);
   

12.2.2 打印输出及解析日期-时间对象

java.util.time提供了格式化以及解析日期-时间对象的能力。

// DateTimeFormatter预定义格式化
LocalDate date = LocalDate.of(2014, 3, 18);
String s1 = date.format(DateTimeFormatter.BASIC_ISO_DATE); // 20140318
String s2 = date.format(DateTimeFormatter.ISO_LOCAL_DATE); // 2014-03-18

// DateTimeFormatter预定义解析
LocalDate date1 = LocalDate.parse(s1, DateTimeFormatter.BASIC_ISO_DATE); // LocalDate.of(2014, 3, 18)
LocalDate date2 = LocalDate.parse(s2, DateTimeFormatter.ISO_LOCAL_DATE); // LocalDate.of(2014, 3, 18)

// DateTimeFormatter自定义格式化
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");
String formattedDate = date.format(formatter); // 18/03/2014
// DateTimeFormatter自定义解析
LocalDate date3 = LocalDate.parse(formattedDate, formatter); // LocalDate.of(2014, 3, 18)

// DateTimeFormatter自定义本地化格式化
DateTimeFormatter italianFormatter = DateTimeFormatter.ofPattern("d. MMMM yyyy", Locale.ITALIAN);
String italianFormat = date.format(italianFormatter); // 18. marzo 2014
// DateTimeFormatter自定义本地化解析
LocalDate date4 = LocalDate.parse(italianFormat, italianFormatter);

// DateTimeFormatter自定义更复杂格式的解析器
public static DateTimeFormatter buildItalianFormatter() {
    DateTimeFormatter italianFormatter = new DateTimeFormatterBuilder()
            .appendText(ChronoField.DAY_OF_MONTH)
            .appendLiteral(". ")
            .appendText(ChronoField.MONTH_OF_YEAR)
            .appendLiteral(" ")
            .appendText(ChronoField.YEAR)
            .parseCaseInsensitive()
            .toFormatter(Locale.ITALIAN);
    return italianFormatter;
}