java - 将大写日期解析为 LocalDate

Question

我正在尝试将字符串 FEBRUARY 2019 解析为 LocalDate。

这是我的方法:

LocalDate month = LocalDate.parse("FEBRUARY 2019", DateTimeFormatter.ofPattern("MMMM yyyy"));

或者设置Locale.US:

LocalDate month = LocalDate.parse("FEBRUARY 2019", DateTimeFormatter.ofPattern("MMMM yyyy", Locale.US));

但我得到的只是以下异常:

Exception in thread "main" java.time.format.DateTimeParseException: Text 'FEBRUARY 2019' could not be parsed at index 0

Answer 1

首先，我建议您输入的不是日期 - 它是年和月。因此，解析为 YearMonth，然后根据需要从中创建一个 LocalDate。我发现最简单的做法是让文本处理代码仅处理文本处理，并在您已经在日期/时间域中时单独执行任何其他转换。

要处理区分大小写的问题，您可以创建一个不区分大小写解析的 DateTimeFormatter。这是一个完整的例子:

import java.time.*;
import java.time.format.*;
import java.util.*;

public class Test {
    public static void main(String[] args) {
        // Note: this would probably be a field somewhere so you don't need
        // to build it every time.
        DateTimeFormatter formatter = new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .appendPattern("MMMM yyyy")
            .toFormatter(Locale.US);

        YearMonth month = YearMonth.parse("FEBRUARY 2019", formatter);
        System.out.println(month);
    }
}

如果您有不同的表示，作为一种可能有用的替代方法，您可以构建一个 map 并将其传递给 DateTimeFormatterBuilder.appendText。 (我只是在以某种方式弄乱代码时才发现这一点。)

import java.time.*;
import java.time.format.*;
import java.time.temporal.*;
import java.util.*;

public class Test {
    public static void main(String[] args) {
        // TODO: Build this map up programmatically instead?            
        Map<Long, String> monthNames = new HashMap<>();
        monthNames.put(1L, "JANUARY");
        monthNames.put(2L, "FEBRUARY");
        monthNames.put(3L, "MARCH");
        monthNames.put(4L, "APRIL");
        monthNames.put(5L, "MAY");
        monthNames.put(6L, "JUNE");
        monthNames.put(7L, "JULY");
        monthNames.put(8L, "AUGUST");
        monthNames.put(9L, "SEPTEMBER");
        monthNames.put(10L, "OCTOBER");
        monthNames.put(11L, "NOVEMBER");
        monthNames.put(12L, "DECEMBER");

        // Note: this would probably be a field somewhere so you don't need
        // to build it every time.
        DateTimeFormatter formatter = new DateTimeFormatterBuilder()
            .appendText(ChronoField.MONTH_OF_YEAR, monthNames)
            .appendLiteral(' ')
            .appendPattern("yyyy")
            .toFormatter(Locale.US);

        YearMonth month = YearMonth.parse("FEBRUARY 2019", formatter);
        System.out.println(month);
    }
}