Java新特性解读JDK8之日期时间处理类

//java.util.Date构造日期时间源码，cdate为实例变量，导致线程不安全
@Deprecated
    public Date(int year, int month, int date, int hrs, int min, int sec) {
        int y = year + 1900;
        // month is 0-based. So we have to normalize month to support Long.MAX_VALUE.
        if (month >= 12) {
            y += month  12;
            month %= 12;
        } else if (month < 0) {
            y += CalendarUtils.floorDivide(month, 12);
            month = CalendarUtils.mod(month, 12);
        }
        BaseCalendar cal = getCalendarSystem(y);
        cdate = (BaseCalendar.Date) cal.newCalendarDate(TimeZone.getDefaultRef());
        cdate.setNormalizedDate(y, month + 1, date).setTimeOfDay(hrs, min, sec, 0);
        getTimeImpl();
        cdate = null;
    }

//Calendar构造函数源码，其中也是使用了实例变量，导致线程不安全
 protected Calendar(TimeZone zone, Locale aLocale)
{
        fields = new int[FIELD_COUNT];
        isSet = new boolean[FIELD_COUNT];
        stamp = new int[FIELD_COUNT];


        this.zone = zone;
        setWeekCountData(aLocale);
    }

//SimpleDateFormat中format方法，calendar为实例变量，导致线程不安全
 @Override
    public StringBuffer format(Date date, StringBuffer toAppendTo,
                               FieldPosition pos)
    {
        pos.beginIndex = pos.endIndex = 0;
        return format(date, toAppendTo, pos.getFieldDelegate());
    }


    // Called from Format after creating a FieldDelegate
    private StringBuffer format(Date date, StringBuffer toAppendTo,
                                FieldDelegate delegate) {
        // Convert input date to time field list
        calendar.setTime(date);


        boolean useDateFormatSymbols = useDateFormatSymbols();


        for (int i = 0; i < compiledPattern.length; ) {
            int tag = compiledPattern[i] >>> 8;
            int count = compiledPattern[i++] & 0xff;
            if (count == 255) {
                count = compiledPattern[i++] << 16;
                count |= compiledPattern[i++];
            }


            switch (tag) {
            case TAG_QUOTE_ASCII_CHAR:
                toAppendTo.append((char)count);
                break;


            case TAG_QUOTE_CHARS:
                toAppendTo.append(compiledPattern, i, count);
                i += count;
                break;


            default:
                subFormat(tag, count, delegate, toAppendTo, useDateFormatSymbols);
                break;
            }
        }
        return toAppendTo;
    }

//LocalDate线程安全类,获取LocalDate对象create方法使用 new 
//LocalTime和Localdatetime也都是线程安全类，获取对象也都使用new，这里不再列出源码
private static LocalDate create(int year, int month, int dayOfMonth) {
        if (dayOfMonth > 28) {
            int dom = 31;
            switch (month) {
                case 2:
                    dom = (IsoChronology.INSTANCE.isLeapYear(year) ? 29 : 28);
                    break;
                case 4:
                case 6:
                case 9:
                case 11:
                    dom = 30;
                    break;
            }
            if (dayOfMonth > dom) {
                if (dayOfMonth == 29) {
                    throw new DateTimeException("Invalid date 'February 29' as '" + year + "' is not a leap year");
                } else {
                    throw new DateTimeException("Invalid date '" + Month.of(month).name() + " " + dayOfMonth + "'");
                }
            }
        }
        return new LocalDate(year, month, dayOfMonth);

 //DateTimeFormatter线程安全,StringBuilder和new DateTimePrintContext保证线程安全
 public String format(TemporalAccessor temporal) {
        StringBuilder buf = new StringBuilder(32);
        formatTo(temporal, buf);
        return buf.toString();
    }


public void formatTo(TemporalAccessor temporal, Appendable appendable) {
        Objects.requireNonNull(temporal, "temporal");
        Objects.requireNonNull(appendable, "appendable");
        try {
            DateTimePrintContext context = new DateTimePrintContext(temporal, this);
            if (appendable instanceof StringBuilder) {
                printerParser.format(context, (StringBuilder) appendable);
            } else {
                // buffer output to avoid writing to appendable in case of error
                StringBuilder buf = new StringBuilder(32);
                printerParser.format(context, buf);
                appendable.append(buf);
            }
        } catch (IOException ex) {
            throw new DateTimeException(ex.getMessage(), ex);
        }
    }

package com.example.datedemo;


import java.time.Duration;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;


/**
 * JDK8之前处理时间的API:SimpleDateFormat,Calendar,java.util.date是非线程安全的，日期/时间处理麻烦
 * JDK8处理时间包 java.time,核心类 LocalDate,LocalTime,Localdatetime
 * DateJDK8.java
 * @author twotwoseven
 * 2019年12月30日
 */
public class DateJDK8 {
/**
 * 日期时间格式化
 * JDK8之前：SimpleDateFormat处理格式化，非线程安全的
 * JDK8: DateTimeFormatter 线程安全的日期与时间
 * @return
 */
public static String getDate(String StrFormat){
  LocalDateTime localDateTime = LocalDateTime.now();
  System.out.println(localDateTime);
  DateTimeFormatter dateTimeFormatter= DateTimeFormatter.ofPattern(StrFormat);
  String format = dateTimeFormatter.format(localDateTime);
  System.out.println(format);
  return format;
}
/**
 * 获取指定的日期时间对象
 * @return
 */
public static LocalDateTime getLocalDateTime(){
  LocalDateTime of = LocalDateTime.of(2020, 12, 12, 12, 21,21);
  return of;
}
/**
 * 计算日期时间差
 */
public static void duration(){
  LocalDateTime today = LocalDateTime.now();
  System.out.println(today);
  LocalDateTime changeDate=LocalDateTime.of(2020, 11, 11, 11, 11,11);
  System.out.println(changeDate);
  Duration between = Duration.between(today, changeDate);
  System.out.println(between.toDays());//相差天数
  System.out.println(between.toHours());//相差小时
  System.out.println(between.toMinutes());//相差分钟
  System.out.println(between.toMillis());//相差秒
}


/**
 * 测试
 * @param args
 */
public static void main(String[] args) {
  LocalDate now = LocalDate.now();
  System.out.println(now.getYear());
  System.out.println(now.getDayOfWeek());
  System.out.println("-----------------");
  String date = DateJDK8.getDate("yyyy-MM-dd HH:mm:ss");
  System.out.println(date);
  System.out.println("-----------------");
  System.out.println(DateJDK8.getLocalDateTime());
  System.out.println("-----------------");
  DateJDK8.duration();
}
}