DateUtil.format(new Date(),DateUtil.PATTERN_DATETIME) 方法的作用

`DateUtil.format(new Date(),DateUtil.PATTERN_DATETIME)` 方法的作用是将当前时间按照指定的格式进行格式化输出。其中第一个参数 `new Date()` 表示获取当前时间，第二个参数 `DateUtil.PATTERN_DATETIME` 则表示输出的格式为 `yyyy-MM-dd HH:mm:ss`。

例如，如果当前时间为 2022年5月20日 14点30分10秒，则该方法将输出字符串 `"2022-05-20 14:30:10"`。这个方法通常用于将日期时间类型转换为字符串类型，以便于输出或存储。

相关问题

LocalDateTimeUtil.of(date).withDayOfMonth(i)

根据提供的引用内容，我们可以看出`LocalDateTimeUtil.of(date).withDayOfMonth(i)`是一个自定义的方法，它的作用是将传入的`date`转换为`LocalDateTime`对象，并将其日期修改为`i`号。具体实现代码如下：

public static LocalDateTime of(Date date) {
    return LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault());
}

public static LocalDateTime of(Date date, ZoneId zone) {
    return LocalDateTime.ofInstant(date.toInstant(), zone);
}

public static LocalDateTime ofEpochSecond(long epochSecond, ZoneOffset offset) {
    return LocalDateTime.ofInstant(Instant.ofEpochSecond(epochSecond), offset);
}

public static LocalDateTime ofEpochMilli(long epochMilli, ZoneOffset offset) {
    return LocalDateTime.ofInstant(Instant.ofEpochMilli(epochMilli), offset);
}

public static LocalDateTime of(int year, int month, int dayOfMonth, int hour, int minute, int second) {
    return LocalDateTime.of(year, month, dayOfMonth, hour, minute, second);
}

public static LocalDateTime of(int year, int month, int dayOfMonth, int hour, int minute) {
    return LocalDateTime.of(year, month, dayOfMonth, hour, minute);
}

public static LocalDateTime of(int year, int month, int dayOfMonth) {
    return LocalDateTime.of(year, month, dayOfMonth, 0, 0);
}

public static LocalDateTime of(LocalDate date, LocalTime time) {
    return LocalDateTime.of(date, time);
}

public static LocalDateTime of(int year, Month month, int dayOfMonth, int hour, int minute, int second) {
    return LocalDateTime.of(year, month, dayOfMonth, hour, minute, second);
}

public static LocalDateTime of(int year, Month month, int dayOfMonth, int hour, int minute) {
    return LocalDateTime.of(year, month, dayOfMonth, hour, minute);
}

public static LocalDateTime of(int year, Month month, int dayOfMonth) {
    return LocalDateTime.of(year, month, dayOfMonth, 0, 0);
}

public static LocalDateTime of(LocalDate date) {
    return LocalDateTime.of(date, LocalTime.MIN);
}

public static LocalDateTime of(LocalTime time) {
    return LocalDateTime.of(LocalDate.now(), time);
}

public static LocalDateTime of(int year, int dayOfYear, LocalTime time) {
    return LocalDateTime.of(LocalDate.ofYearDay(year, dayOfYear), time);
}

public static LocalDateTime ofInstant(Instant instant, ZoneId zone) {
    return LocalDateTime.ofInstant(instant, zone);
}

public static LocalDateTime parse(CharSequence text) {
    return LocalDateTime.parse(text);
}

public static LocalDateTime parse(CharSequence text, DateTimeFormatter formatter) {
    return LocalDateTime.parse(text, formatter);
}

public static String format(LocalDateTime dateTime, String pattern) {
    DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);
    return dateTime.format(formatter);
}

public static String format(LocalDateTime dateTime, DateTimeFormatter formatter) {
    return dateTime.format(formatter);
}

public static LocalDateTime now() {
    return LocalDateTime.now();
}

public static LocalDateTime now(Clock clock) {
    return LocalDateTime.now(clock);
}

public static LocalDateTime now(ZoneId zone) {
    return LocalDateTime.now(zone);
}

public static LocalDateTime now(ZoneOffset offset) {
    return LocalDateTime.now(offset);
}

public static LocalDateTime plusYears(LocalDateTime dateTime, long years) {
    return dateTime.plusYears(years);
}

public static LocalDateTime plusMonths(LocalDateTime dateTime, long months) {
    return dateTime.plusMonths(months);
}

public static LocalDateTime plusWeeks(LocalDateTime dateTime, long weeks) {
    return dateTime.plusWeeks(weeks);
}

public static LocalDateTime plusDays(LocalDateTime dateTime, long days) {
    return dateTime.plusDays(days);
}

public static LocalDateTime plusHours(LocalDateTime dateTime, long hours) {
    return dateTime.plusHours(hours);
}

public static LocalDateTime plusMinutes(LocalDateTime dateTime, long minutes) {
    return dateTime.plusMinutes(minutes);
}

public static LocalDateTime plusSeconds(LocalDateTime dateTime, long seconds) {
    return dateTime.plusSeconds(seconds);
}

public static LocalDateTime plusNanos(LocalDateTime dateTime, long nanos) {
    return dateTime.plusNanos(nanos);
}

public static LocalDateTime minusYears(LocalDateTime dateTime, long years) {
    return dateTime.minusYears(years);
}

public static LocalDateTime minusMonths(LocalDateTime dateTime, long months) {
    return dateTime.minusMonths(months);
}

public static LocalDateTime minusWeeks(LocalDateTime dateTime, long weeks) {
    return dateTime.minusWeeks(weeks);
}

public static LocalDateTime minusDays(LocalDateTime dateTime, long days) {
    return dateTime.minusDays(days);
}

public static LocalDateTime minusHours(LocalDateTime dateTime, long hours) {
    return dateTime.minusHours(hours);
}

public static LocalDateTime minusMinutes(LocalDateTime dateTime, long minutes) {
    return dateTime.minusMinutes(minutes);
}

public static LocalDateTime minusSeconds(LocalDateTime dateTime, long seconds) {
    return dateTime.minusSeconds(seconds);
}

public static LocalDateTime minusNanos(LocalDateTime dateTime, long nanos) {
    return dateTime.minusNanos(nanos);
}

public static long between(LocalDateTime startInclusive, LocalDateTime endExclusive, ChronoUnit unit) {
    return unit.between(startInclusive, endExclusive);
}

public static boolean isBefore(LocalDateTime dateTime1, LocalDateTime dateTime2) {
    return dateTime1.isBefore(dateTime2);
}

public static boolean isAfter(LocalDateTime dateTime1, LocalDateTime dateTime2) {
    return dateTime1.isAfter(dateTime2);
}

public static boolean isEqual(LocalDateTime dateTime1, LocalDateTime dateTime2) {
    return dateTime1.isEqual(dateTime2);
}

public static boolean isLeapYear(int year) {
    return Year.isLeap(year);
}

public static int getYear(LocalDateTime dateTime) {
    return dateTime.getYear();
}

public static Month getMonth(LocalDateTime dateTime) {
    return dateTime.getMonth();
}

public static int getMonthValue(LocalDateTime dateTime) {
    return dateTime.getMonthValue();
}

public static int getDayOfMonth(LocalDateTime dateTime) {
    return dateTime.getDayOfMonth();
}

public static int getDayOfYear(LocalDateTime dateTime) {
    return dateTime.getDayOfYear();
}

public static DayOfWeek getDayOfWeek(LocalDateTime dateTime) {
    return dateTime.getDayOfWeek();
}

public static int getHour(LocalDateTime dateTime) {
    return dateTime.getHour();
}

public static int getMinute(LocalDateTime dateTime) {
    return dateTime.getMinute();
}

public static int getSecond(LocalDateTime dateTime) {
    return dateTime.getSecond();
}

public static int getNano(LocalDateTime dateTime) {
    return dateTime.getNano();
}

public static LocalDate toLocalDate(LocalDateTime dateTime) {
    return dateTime.toLocalDate();
}

public static LocalTime toLocalTime(LocalDateTime dateTime) {
    return dateTime.toLocalTime();
}

public static Date toDate(LocalDateTime dateTime) {
    return Date.from(dateTime.atZone(ZoneId.systemDefault()).toInstant());
}

public static Date toDate(LocalDateTime dateTime, ZoneId zone) {
    return Date.from(dateTime.atZone(zone).toInstant());
}

public static Instant toInstant(LocalDateTime dateTime) {
    return dateTime.atZone(ZoneId.systemDefault()).toInstant();
}

public static Instant toInstant(LocalDateTime dateTime, ZoneId zone) {
    return dateTime.atZone(zone).toInstant();
}

public static String toString(LocalDateTime dateTime) {
    return dateTime.toString();
}

public static String toString(LocalDateTime dateTime, String pattern) {
    DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);
    return dateTime.format(formatter);
}

public static String toString(LocalDateTime dateTime, DateTimeFormatter formatter) {
    return dateTime.format(formatter);
}

public static LocalDateTime withYear(LocalDateTime dateTime, int year) {
    return dateTime.withYear(year);
}

public static LocalDateTime withMonth(LocalDateTime dateTime, int month) {
    return dateTime.withMonth(month);
}

public static LocalDateTime withDayOfMonth(LocalDateTime dateTime, int dayOfMonth) {
    return dateTime.withDayOfMonth(dayOfMonth);
}

public static LocalDateTime withDayOfYear(LocalDateTime dateTime, int dayOfYear) {
    return dateTime.withDayOfYear(dayOfYear);
}

public static LocalDateTime withHour(LocalDateTime dateTime, int hour) {
    return dateTime.withHour(hour);
}

public static LocalDateTime withMinute(LocalDateTime dateTime, int minute) {
    return dateTime.withMinute(minute);
}

public static LocalDateTime withSecond(LocalDateTime dateTime, int second) {
    return dateTime.withSecond(second);
}

public static LocalDateTime withNano(LocalDateTime dateTime, int nanoOfSecond) {
    return dateTime.withNano(nanoOfSecond);
}

public static LocalDateTime with(LocalDateTime dateTime, TemporalAdjuster adjuster) {
    return dateTime.with(adjuster);
}

public static LocalDateTime with(LocalDateTime dateTime, TemporalField field, long newValue) {
    return dateTime.with(field, newValue);
}

public static LocalDateTime plus(LocalDateTime dateTime, TemporalAmount amountToAdd) {
    return dateTime.plus(amountToAdd);
}

public static LocalDateTime plus(LocalDateTime dateTime, long amountToAdd, TemporalUnit unit) {
    return dateTime.plus(amountToAdd, unit);
}

public static LocalDateTime minus(LocalDateTime dateTime, TemporalAmount amountToSubtract) {
    return dateTime.minus(amountToSubtract);
}

public static LocalDateTime minus(LocalDateTime dateTime, long amountToSubtract, TemporalUnit unit) {
    return dateTime.minus(amountToSubtract, unit);
}

public static long until(LocalDateTime dateTime, Temporal endExclusive, TemporalUnit unit) {
    return dateTime.until(endExclusive, unit);
}

public static LocalDateTime truncate(LocalDateTime dateTime, TemporalUnit unit) {
    return dateTime.truncatedTo(unit);
}

因此，`LocalDateTimeUtil.of(date).withDayOfMonth(i)`的作用是将传入的`date`转换为`LocalDateTime`对象，并将其日期修改为`i`号。

LocalDateTime.parse(date, dtf);

`LocalDateTime.parse(date, df)` 是 Java 8 中 `java.time` 包下的 `LocalDateTime` 类的一个静态方法，用于将给定的日期字符串（date）解析成 `LocalDateTime` 对象。这里的 `date` 参数通常是一个符合指定日期格式（datetime format, df）的字符串，而 `df` 是一个 `DateTimeFormatter` 对象，用于定义输入字符串的日期时间格式。

具体步骤如下：
1. `DateTimeFormatter` 是一个工厂类，用于根据给定的模式（pattern）解析和格式化日期时间。模式定义了日期和时间的组成，比如 "yyyy-MM-dd HH:mm:ss"。
2. 方法尝试将 `date` 字符串按照 `df` 定义的格式进行解析。如果格式匹配成功，会返回对应的 `LocalDateTime` 对象表示该日期和时间；如果格式不匹配或者字符串无法解析，则会抛出异常，通常是 `DateTimeParseException`。
3. 使用 `LocalDateTime` 你可以单独处理日期和时间部分，而不考虑时区问题，因为 `LocalDateTime` 表示的是在本地时区中的瞬间。