如何将JDK11中的不同日期格式转换为dd-mm-yyyy格式？[复制]

您可以循环访问已知格式并跳过抛出 .DateTimeParseException

注意：如果仅将日期字符串解析为 ，则需要构建格式化程序并指定时间部分是可选的。LocalDateTime

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

public class DateParser {
    public static void main(String[] args) {
        System.out.println(normalizeDate("2023-05-09T05:55:07Z")); // 2023-05-09
        System.out.println(normalizeDate("2023-04-30")); // 2023-04-30
        System.out.println(normalizeDate("08-05-2023")); // 2023-08-05
        System.out.println(normalizeDate("2023-05-09 00:00:00")); // 2023-05-09
        System.out.println(normalizeDate("31-Dec-2021")); // 2021-12-31
        System.out.println(normalizeDate("")); // null
    }

    public static String normalizeDate(String rawDateTimeString) {
        return Optional.ofNullable(parseDateString(rawDateTimeString))
                .map(displayFormat::format)
                .orElse(null);
    }

    private static LocalDateTime parseDateString(String dateString) {
        for (DateTimeFormatter formatter : knownFormats) {
            try {
                return LocalDateTime.parse(dateString, formatter);
            } catch (DateTimeParseException e) {
                continue;
            }
        }
        return null;
    }

    private static final List<DateTimeFormatter> knownFormats = Arrays.asList(
            DateTimeFormatter.ISO_DATE_TIME,
            dateOnlyFormatter("yyyy-MM-dd"),
            dateOnlyFormatter("MM-dd-yyyy"),
            DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"),
            dateOnlyFormatter("dd-MMM-yyyy").withLocale(Locale.ENGLISH));

    private static DateTimeFormatter dateOnlyFormatter(String datePattern) {
        // Credit: https://stackoverflow.com/a/40175568/1762224
        return new DateTimeFormatterBuilder()
                .appendPattern(datePattern)
                .optionalStart()
                .appendPattern(" HH:mm")
                .optionalEnd()
                .parseDefaulting(ChronoField.HOUR_OF_DAY, 0)
                .parseDefaulting(ChronoField.MINUTE_OF_HOUR, 0)
                .toFormatter();
    }

    private static final DateTimeFormatter displayFormat = DateTimeFormatter.ISO_DATE;
}

这是一个修改后的版本，正如 Devin 建议的那样更简单。它完全忽略了时间的概念，在解析时只关注日期。它消除了对该方法的需求（如上所示）。dateOnlyFormatter

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

public class DateParser {
    public static void main(String[] args) {
        System.out.println(normalizeDate("2023-05-09T05:55:07Z")); // 2023-05-09
        System.out.println(normalizeDate("2023-04-30")); // 2023-04-30
        System.out.println(normalizeDate("08-05-2023")); // 2023-08-05
        System.out.println(normalizeDate("2023-05-09 00:00:00")); // 2023-05-09
        System.out.println(normalizeDate("31-Dec-2021")); // 2021-12-31
        System.out.println(normalizeDate("")); // null
    }

    public static String normalizeDate(String rawDateTimeString) {
        return Optional.ofNullable(parseDateString(rawDateTimeString))
                .map(displayFormat::format)
                .orElse(null);
    }

    private static LocalDate parseDateString(String dateString) {
        for (DateTimeFormatter formatter : knownFormats) {
            try {
                return LocalDate.parse(dateString, formatter);
            } catch (DateTimeParseException e) {
                continue;
            }
        }
        return null;
    }

    private static final List<DateTimeFormatter> knownFormats = Arrays.asList(
            DateTimeFormatter.ISO_DATE_TIME,
            DateTimeFormatter.ofPattern("yyyy-MM-dd"),
            DateTimeFormatter.ofPattern("MM-dd-yyyy"),
            DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"),
            DateTimeFormatter.ofPattern("dd-MMM-yyyy").withLocale(Locale.ENGLISH));

    private static final DateTimeFormatter displayFormat = DateTimeFormatter.ISO_DATE;
}

这种方法简单易懂。以下是 parseDateTime 函数的所有功能：

1. 设置输出格式
2. 设置所有可能的输入格式
3. 循环访问每种输入格式，直到找到正确的格式
4. 以指定的输出格式返回日期/时间

注意如果传递给函数的 String 不是 5 种指定的输入格式之一，则它将返回 null。这应该可以很容易地看出它是否成功！

如果您需要更多信息来帮助添加更多格式，请参阅 DateTimeFormatter 文档：https://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html#ISO_DATE

import java.time.*;
import java.time.format.DateTimeFormatter;

public class Main {
     public static void main(String[] args) {
        String[] inputDates = {
                "2023-04-30T05:55:07Z",
                "2023-04-30",
                "30-04-2023",
                "2023-04-30 00:00:00",
                "30-Apr-2023"
        };

        for(String date : inputDates)
            System.out.println(date + "\t->\t" + parseDateTime(date));
    }


    private static String parseDateTime(String currentDate){
        //Desired Output Pattern
        DateTimeFormatter outputFormat = DateTimeFormatter.ofPattern("dd-MM-yyyy");

        //All Possible Input Patterns
        DateTimeFormatter[] formatters = {
            DateTimeFormatter.ISO_LOCAL_DATE,
            DateTimeFormatter.ofPattern("dd-MM-yyyy"),
            DateTimeFormatter.ofPattern("dd-MMM-yyyy"),
            DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"),
            DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss'Z'")
        };

        //Iterate over each pattern until it finds the correct one
        for(DateTimeFormatter currFormatter : formatters){
            try{
                return LocalDate.parse(currentDate, currFormatter).format(outputFormat);
            } catch(Exception ignored){
                //Current formatter did not work, so lets try the next one
            }
        }
        return null; // String was not one of those 5 formats
    }
}```