【Java深层系列】「技术盲区」让我们一起完全吃透针对于时间和日期相关的API指南

// Alternate ISO 8601 format without fractional seconds
private static final String ALTERNATIVE_ISO8601_DATE_FORMAT = "yyyy-MM-dd'T'HH:mm:ss'Z'";
  private static DateFormat getAlternativeIso8601DateFormat() {
        SimpleDateFormat df = new SimpleDateFormat(ALTERNATIVE_ISO8601_DATE_FORMAT, Locale.US);
        df.setTimeZone(new SimpleTimeZone(0, "GMT"));
        return df;
  }
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date-time = [ day "," ] date time ; dd mm yy
                                                     ; hh:mm:ss zzz
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"EEE, dd MMM yyyy HH:mm:ss z"
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// RFC 822 Date Format
private static final String RFC822_DATE_FORMAT = "EEE, dd MMM yyyy HH:mm:ss z";
private static DateFormat getRfc822DateFormat() {
        SimpleDateFormat rfc822DateFormat =
                new SimpleDateFormat(RFC822_DATE_FORMAT, Locale.US);
        rfc822DateFormat.setTimeZone(new SimpleTimeZone(0, "GMT"));
        return rfc822DateFormat;
}
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SimpleDateFormat df1=new SimpleDateFormat("GGGG yyyy/MMMM/dd HH:mm:ss EEE aaa zzzz",Locale.CHINA);
SimpleDateFormat df2=new SimpleDateFormat("GGGG yyyy/MMMM/dd HH:mm:ss EEE aaa zzzz",Locale.US);
//公元 2016/三月/27 23:32:10 星期日 下午 中国标准时间
//AD 2016/March/27 23:32:10 Sun PM China Standard Time
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public Date() {
        this(System.currentTimeMillis());
 }
 public Date(long date) {
      fastTime = date;
}
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long time = System.currentTimeMillis();
System.out.println(time=(time/1000));
System.out.println("秒："+ time%60);
System.out.println(time=(time/60));
System.out.println("分钟："+time%60);
System.out.println(time=(time/60));
System.out.println("小时："+time%24);
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private static final BaseCalendar getCalendarSystem(BaseCalendar.Date cdate) {
        if (jcal == null) {
            return gcal;
        }
        if (cdate.getEra() != null) {
            return jcal;
        }
        return gcal;
    }
    synchronized private static final BaseCalendar getJulianCalendar() {
        if (jcal == null) {
            jcal = (BaseCalendar) CalendarSystem.forName("julian");
        }
        return jcal;
    }
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private static final BaseCalendar getCalendarSystem(int year) {
        if (year >= 1582) {
            return gcal;
        }
        return getJulianCalendar();
    }
    private static final BaseCalendar getCalendarSystem(long utc) {
        // Quickly check if the time stamp given by `utc' is the Epoch
        // or later. If it's before 1970, we convert the cutover to
        // local time to compare.
        if (utc >= 0
            || utc >= GregorianCalendar.DEFAULT_GREGORIAN_CUTOVER
                        - TimeZone.getDefaultRef().getOffset(utc)) {
            return gcal;
        }
        return getJulianCalendar();
    }
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public static final int FIELD_UNDEFINED = -2147483648;
    public static final long TIME_UNDEFINED = -9223372036854775808L;
    private Era era;
    private int year;
    private int month;
    private int dayOfMonth;
    private int dayOfWeek;
    private boolean leapYear;
    private int hours;
    private int minutes;
    private int seconds;
    private int millis;
    private long fraction;
    private boolean normalized;
    private TimeZone zoneinfo;
    private int zoneOffset;
    private int daylightSaving;
    private boolean forceStandardTime;
    private Locale locale;
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@Deprecated
    public static long parse(String s) {
   ... ...
            // Parse 2-digit years within the correct default century.
            if (year < 100) {
                synchronized (Date.class) {
                    if (defaultCenturyStart == 0) {
                        defaultCenturyStart = gcal.getCalendarDate().getYear() - 80;
                    }
                }
                year += (defaultCenturyStart / 100) * 100;
                if (year < defaultCenturyStart) year += 100;
            }
            ... ...
    }
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public static Calendar getInstance() {
        return createCalendar(TimeZone.getDefault(), Locale.getDefault(Locale.Category.FORMAT));
    }
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//2000-8-31
        Calendar cal1 = Calendar.getInstance();
        cal1.set(2000, 7, 31, 0, 0 , 0);
        //应该是 2000-9-31，也就是 2000-10-1
        cal1.set(Calendar.MONTH, Calendar.SEPTEMBER);
        //如果 Calendar 转化到 2000-10-1，那么现在的结果就该是 2000-10-30
        cal1.set(Calendar.DAY_OF_MONTH, 30);
        //输出的是2000-9-30，说明 Calendar 不是马上就刷新其内部的记录
        System.out.println(cal1.getTime());
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private static final ThreadLocal<DateFormat> df = new ThreadLocal<DateFormat>() { 
        @Override 
        protected DateFormat initialValue() { 
                return new SimpleDateFormat("yyyy-MM-dd"); 
        }
 };
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public static LocalDateTime parse(CharSequence text, DateTimeFormatter formatter) {
    Objects.requireNonNull(formatter, "formatter");
    return formatter.parse(text, LocalDateTime::from);
}
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public <T> T parse(CharSequence text, TemporalQuery<T> query) {
   ... ...
}
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public static LocalDateTime from(TemporalAccessor temporal) {
    .... ...     
}
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//与下列表示相同
x ->  LocalDateTime.from(x)
//相当于
new TemporalQuery<LocalDateTime>(){
       @Override
        public LocalDateTime queryFrom(TemporalAccessor temporal) {
             return LocalDateTime.from(temporal);
        }
};