无法使用DateTimeFormatter解析月+日

Question

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;
import java.util.ArrayList;
import java.util.List;
import java.text.SimpleDateFormat;  
import java.util.Date;  
import java.util.Locale;

// one class needs to have a main() method
public class HelloWorld
{
  // arguments are passed using the text field below this editor
  public static void main(String[] args) throws Exception
  {

    String str = "Mon 21st May";
    DateTimeFormatter parseFormatter = DateTimeFormatter.ofPattern("EEEE d['st']['nd']['rd']['th'] MMMM", Locale.ENGLISH);
    LocalDate datetext = LocalDate.parse(str, parseFormatter);

  }
}

  public static void main(String[] args) throws Exception
  {

    String str = "Tue 21st May";
    DateTimeFormatter parseFormatter = DateTimeFormatter.ofPattern("EEE d['st']['nd']['rd']['th'] MMMM", Locale.ENGLISH);
    LocalDate datetext = LocalDate.parse(str, parseFormatter);

  }
}

错误：

线程“main”java.time.format.dateTimeParseException：无法解析文本“Tue 21 May”：无法从TemporalAccessor获取LocalDate：{DayOfWeek=2,DayOfMonth=21,MonthOfYear=5},类型为java.time.format.dateTimeFormatter.createError(dateTimeFormatter.java:1920)在java.time.format.dateTimeFormatter.jave:1855)在java.time.LocalDate.parse（dateTimeFormatter.java:1855)在java.time.LocalDate.parse（LocalDate.java:400)在EtimeException：无法从TemporalAccessor获取LocalDate：{DayOfWeek=2,DayOfMonth=21,MonthOfYear=5},类型为java.time.LocalDate.from（LocalDate.java:368)的ISO at java.time.LocalDate.from（LocalDate.java:368)at java.time.format.parse.query（parsed.java:226)at java.time.format.dateTimeFormatter.parse（dateTimeFormatter.jave:1851)...

Answer 1

如果要在没有年份的情况下解析月份和日期，请使用monthday:

    String str = "Mon 21st May";
    DateTimeFormatter parseFormatter = DateTimeFormatter.ofPattern("EEE d['st']['nd']['rd']['th'] MMMM", Locale.ENGLISH);
    MonthDay md = MonthDay.parse(str, parseFormatter);
    System.out.println(md);

输出为：

--05-21

    LocalDate datetext = md.atYear(Year.now(ZoneId.of("Europe/London")).getValue());
    System.out.println(datetext);

    String str = "Tue 21st May";
    DateTimeFormatter parseFormatter = new DateTimeFormatterBuilder()
            .appendPattern("EEE d['st']['nd']['rd']['th'] MMMM")
            .parseDefaulting(ChronoField.YEAR, Year.now(ZoneId.of("Europe/London")).getValue())
            .toFormatter(Locale.ENGLISH);

    LocalDate datetext = LocalDate.parse(str, parseFormatter);

    DateTimeFormatter outputFormatter = DateTimeFormatter.ofPattern("EEEE d MMMM", Locale.ENGLISH);
    System.out.println(datetext.format(outputFormatter));

5月21日星期二

我可能不知道年份，因为我试图在应用程序中查看日期，但有些日期可能是今年，有些可能是明年，但这些日期没有提供年份

下面的完整示例假设日期在从今天起的未来3年内，并检测星期几正确的年份。一旦成功，它就会以您想要的格式打印出来。

    String str = "Wed 20th May";
    ZoneId zone = ZoneId.of("Europe/London");
    LocalDate today = LocalDate.now(zone);
    int currentYear = today.getYear();
    LocalDate datetext = null;
    final int maxYearsFromToday = 3;
    for (int year = currentYear; year <= currentYear + maxYearsFromToday; year++) {
        DateTimeFormatter parseFormatter = new DateTimeFormatterBuilder()
                .appendPattern("EEE d['st']['nd']['rd']['th'] MMMM")
                .parseDefaulting(ChronoField.YEAR, year)
                .toFormatter(Locale.ENGLISH);

        try {
            datetext = LocalDate.parse(str, parseFormatter);
            System.out.println("Day of week matched for year " + year);
            break;
        } catch (DateTimeParseException dtpe) {
            // Ignore, try next year
        }
    }

    DateTimeFormatter outputFormatter = DateTimeFormatter.ofPattern("EEEE d MMMM", Locale.ENGLISH);
    if (datetext == null) {
        System.out.println("Could not parse date;"
                + " possibly the day of week didn’t match for any year in the range "
                + currentYear + " through " + (currentYear + maxYearsFromToday));
    } else if (datetext.isBefore(today) || datetext.isAfter(today.plusYears(maxYearsFromToday))) {
        System.out.println("Date is out of range");
    } else {
        System.out.println("Successfully parsed: " + datetext.format(outputFormatter));
    }

Day of week matched for year 2020
Successfully parsed: Wednesday 20 May