将GregorianCalendar转换为新的Datetime类型，反之亦然

import java.time.LocalDate;

import java.time.LocalDateTime;

import java.time.LocalTime;
/*
nowjava
*/

import java.time.OffsetDateTime;

import java.time.OffsetTime;

import java.time.ZoneId;

import java.time.ZonedDateTime;


import java.util.GregorianCalendar;

import java.util.TimeZone;


public class Main {

  public static void main(String[] args) {

    // Create a GC for the default time zone
    /** from 
    时 代 J a v a - nowjava.com**/

    GregorianCalendar gc = new GregorianCalendar(2017, 1, 11, 15, 45, 50);

    System.out.println("Gregorian Calendar: " + gc.getTime());


    // Convert the GC to a LocalDate

    LocalDate ld = gc.toZonedDateTime().toLocalDate();

    System.out.println("Local Date: " + ld);


    // Convert the GC to a LocalTime

    LocalTime lt = gc.toZonedDateTime().toLocalTime();

    System.out.println("Local Time: " + lt);


    // Convert the GC to a LocalDateTime

    LocalDateTime ldt = gc.toZonedDateTime().toLocalDateTime();

    System.out.println("Local DateTime: " + ldt);


    // Convert the GC to an OffsetDate

    OffsetDateTime od = gc.toZonedDateTime().toOffsetDateTime();

    System.out.println("Offset Date: " + od);


    // Convert the GC to an OffsetTime

    OffsetTime ot = gc.toZonedDateTime().toOffsetDateTime().toOffsetTime();

    System.out.println("Offset Time: " + ot);


    // Convert the GC to an ZonedDateTime

    ZonedDateTime zdt = gc.toZonedDateTime();

    System.out.println("Zoned DateTime: " + zdt);


    // Convert the ZonedDateTime to a GC. In GC month starts at 0

    // and in new API at 1