Java日期格式化如何避免YYYY引发的时间异常

在编程中，日期格式化是一个常见的任务。使用不同的格式化选项可能会导致一些意外的结果。最近遇到一个问题，就是使用YYYY格式化选项会导致时间异常。

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

    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    SimpleDateFormat sdf2 = new SimpleDateFormat("YYYY-MM-dd HH:mm:ss");
   
    String time = "2023-12-31 23:59:59";
    System.out.printf("yyyy-MM-dd HH:mm:ss: %s\n",sdf.format(sdf.parse(time)));
    System.out.printf("YYYY-MM-dd HH:mm:ss: %s\n",sdf2.format(sdf2.parse(time)));

    System.out.println("======================================");
    String time2 = "2023-11-31 23:59:59"; //11月没有31号
    System.out.printf("yyyy-MM-dd HH:mm:ss: %s\n",sdf.format(sdf.parse(time2)));
    System.out.printf("YYYY-MM-dd HH:mm:ss: %s\n",sdf2.format(sdf2.parse(time2)));

    System.out.println("======================================");
    String time3 = "2023-10-31 23:59:59";
    System.out.printf("yyyy-MM-dd HH:mm:ss: %s\n",sdf.format(sdf.parse(time3)));
    System.out.printf("YYYY-MM-dd HH:mm:ss: %s\n",sdf2.format(sdf2.parse(time3)));
}

输出结果

yyyy-MM-dd javascriptHH:mm:ss: 2023-12-31 23:59:59

YYYY-MM-dd HH:mm:ss: 2023-01-01 23:59:59

======================================

yyyy-MM-dd HH:mm:ss: 2023-12-01 23:59:59

YYYY-MM-dd HH:mm:ss: 2023-01-01 23:59:59

======================================

yyyy-MM-dd HH:mm:ss: 2023-10-31 23:http://www.devze.com59:59

YYYY-MM-dd HH:mm:ss: 2023-01-01 23:59:59

网上查阅说大写的YYYY表示一个基于周的年份，它是根据周计算的年份，而不是基于日历的年份。通常情况下，两者的结果是相同的，但在跨年的第一周或最后一周可能会有差异。但这里发现无论怎么调整时间，YYYY-MM-dd HH:mm:ss格式化后一直是2023-01-01 23:59:59，不仅仅是在跨年的时候出现问题，具体原因尚不清楚

如何避免

定义通用的格式类，所有使用日期格式的地方都引用这个类，这个类中就定义好yyyy-MM-dd格式即可，这样就不会出现有人手误给大家埋雷了。

public class LocalDateUtils {

    /**
     * 显示年月日时分秒，例如 2023-10-31 09:51:53.
     */
    public static final String DATETIME_PATTERN = "yyyy-MM-dd HH:mm:ss";

    /**
     * 仅显示年月日，例如 2023-10-31.
     */
    public static final String DATE_PATTERN = "yyyy-MM-dd";

    private static final String YEAR = "year";
    private static final String MONTH = "month";
    private static final String WEEK = "week";
    private static final String DAY = "day";

    /**
     * 将日期转换为字符串，格式为：yyyy-MM-dd HH:mm:ss
     */
    public static String getLocalDateTimeStr(LocalDateTime localDateTime) {
        return format(localDateTime, DATETIME_PATTERN);
    }

    /**
     * 将日期转换为字符串，格式为：yyyy-MM-dd
     */
    public static String getLocalDateStr(LocalDateTime localDateTime) {
        return format(localDateTime, DATE_PATTERN);
    }


    /**
     * 将字符串转换为日期，格式为：yyyy-MM-dd HH:mm:ss
     */
    public static LocalDateTime parseLocalDateTime(String localDateTimeStr) {
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern(DATETIME_PATTERN);
        return LocalDateTime.parse(localDateTimeStr, dateTimeFormatter);
    }

    /**
     * 将字符串转换为日期，格式为：yyyy-MM-dd
     */
    public static LocalDate parseLocalDate(String localDateStr) {
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern(DATE_PATTERN);
        return LocalDate.parse(localDateStr, dateTimeFormatter);
    }


    /**
     * 将字符串转日期成Long类型的时间戳
     */
    public static Long convertLocalDateTimeToLong(String time) {
        LocalDateTime parse = parse(time, DATETIME_PATTERN);
        return LocalDateTime.from(parse).atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
    }

    /**
     * 将字符串转日期成Long类型的时间戳
     */
    public static Long convertLocalDateToLong(String time) {
        LocalDateTime parse = parse(time, DATE_PATTERN);
        return LocalDateTime.from(parse).atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
    }

    public static LocalDateTime parse(String time, String pattern) {
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern(pattern);
        return LocalDateTime.parse(time, dateTimeFormatter);
    }


    /**
     * 将Long类型的时间戳转换成String 类型的时间格式
     */
    public static String getLocalDateTimeStr(Long time) {
        return format(LocalDateTime.ofInstant(Instant.ofEpochMilli(time), ZoneId.systemDefault()), DATETIME_PATTERN);
    }

    /**
     * 将Long类型的时间戳转换成String 类型的时间格式，时间格式为：yyyy-MM-dd
     */
    public static String getLocalDateStr(Long time) {
        return format(LocalDateTime.ofInstant(Instant.ofEpochMilli(time), ZoneId.systemDefault()), DATE_PATTERN);
    }

    /**
     * 获取日期时间字符串
     */
    public static String format(TemporalAccessor temporal, String pattern) {
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern(pattern);
        return dateTimeFormatter.format(temporal);
    }


    /**
     * 取本月第一天
     */
    public static LocalDate firstDayOfThisMonth() {
        LocalDate today = LocalDate.now();
        return today.with(TemporalAdjusters.firstDayOfMonth());
    }

    /**
     * 取本月第N天
     */
    public static LocalDate dayOfThisMonth(int n) {
        LocalDate today = LocalDate.now();
        return today.withDayOfMonth(n);
    }

    /**
     * 取本月最后一天
     */
    public static LocalDate lastDayOfThisMonth() {
        LocalDate today = LocalDate.now();
        return today.with(TemporalAdjusters.lastDayOfMonth());
    }


    /**
     * 获取指定日期时间加上指定数量日期时间单位之后的日期时间.
     */
    public static LocalDateTime plus(LocalDateTime localDateTime, int num, ChronoUnit chronoUnit) {
        return localDateTime.plus(num, chronoUnit);
    }

    /**
     * 获取指定日期时间减去指定数量日期时间单位之后的日期时间.
     */
    public static LocalDateTime minus(LocalDateTime localDateTime, int num, ChronoUnit chronoUnit) {
        return localDateTime.minus(num, chronoUnit);
    }

    /**
     * 根据ChronoUnit计算两个日期时间之间相隔日期时间
     */
    public static long getChronoUnitBetween(LocalDateTime start, LocalDateTime end, ChronoUnit chronoUnit) {
        return Math.abs(start.until(end, chronoUnit));
    }

    /**
     * 根据ChronoUnit计算两个日期之间相隔年数或月数或天数
     */
    public static long getChronoUnitBetween(LocalDate start, LocalDate end, ChronoUnit chronoUnit) {
        return Math.abs(start.until(end, chronoUnit));
    }


    /**
     * 切割日期。按照周期切割成小段日期段。例如： <br>
     *
     * @param startDate 开始日期（yyyy-MM-dd）
     * @param endDate   结束日期（yyyy-MM-dd）
     * @param period    周期（天，周，月，年）
     * @return 切割之后的日期集合
     * <li>startDate="2023-10-27",endDate="2023-10-31",period="day"</li>
     * <li>结果为：[2023-10-27, 2023-10-28, 2023-10-29, 2023-10-03,2023-10-31]</li><br>
     * <li>startDate="2023-10-27",endDate="2023-10-31",period="week"</li>
     * <li>结果为：[2023-10-27,2023-10-31]</li><br>
     * <li>startDate="2023-10-27",endDate="2023-10-31",period="month"</li>
     * <li>结果为：[2023-10-27,2023-10-31]</li><br>
     * <li>startDate="2023-10-27",endDate="2023-10-31",period="year"</li>
     * <li>结果为：[2023-10-27,2023-10-31]</li><br>
     */
    public static List<String> listDateStrs(String startDate, String endDwww.devze.comate, String period) {
        List<String> result = new ArrayList<>();
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern(DATE_PATTERN);
        LocalDate end = LocalDate.parse(endDate, dateTimeFormatter);
        LocalDate start = LocalDate.parse(startDate, dateTimeFormatter);
        LocalDate tmp = start;
        switch (period) {
            case DAY:
                while (start.isBefore(end) || start.isEqual(end)) {
                    result.add(start.toString());
                    start = start.plusDays(1);
                }
                break;
            case WEEK:
                while (tmp.isBefore(end) ||编程客栈 tmp.isEqual(end)) {
                    if (tmp.plusDays(6).isAfter(end)) {
                        result.add(tmp.toString() + "," + end);
                    } else {
                        result.add(tmp.toString() + "," + tmp.plusDays(6));
                    }
                    tmp = tmp.plusDays(7);
                }
                break;
            case MONTH:
                while (tmp.isBefore(end) || tmp.isEqual(end)) {
                    LocalDate lastDayOfMonth = tmp.with(TemporalAdjusters.lastDayOfMonth());
                    if (lastDayOfMonth.isAfter(end)) {
                        result.add(tmp.toString() + "," + end);
                    } else {
                        result.add(tmp.toString() + "," + lastDayOfMonth);
                    }
                    tmp = lastDayOfMonth.plusDays(1);
                }
   javascript             break;
            case YEAR:
                while (tmp.isBefore(end) || tmp.isEqual(end)) {
                    LocalDate lastDayOfYear = tmp.with(TemporalAdjusters.lastDayOfYear());
                    if (lastDayOfYear.isAfter(end)) {
                        result.add(tmp.toString() + "," + end);
                    } else {
                        result.add(tmp.toString() + "," + lastDayOfYear);
                    }
                    tmp = lastDayOfYear.plusDays(1);
                }
                break;
            default:
                break;
        }
        return result;
    }
}

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