Java8 时间类型之间的转换，代码如下
public static void main(String[] args) {
LocalDateTime localDateTime = LocalDateTime.now();
LocalDate localDate = LocalDate.now();
Date date = new Date();
Calendar calendar = Calendar.getInstance();
System.out.println("Date 转 LocalDateTime：" + LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault()));
System.out.println("Calendar 转 LocalDateTime：" + LocalDateTime.ofInstant(calendar.toInstant(), ZoneId.systemDefault()));
System.out.println("Calendar 转 Date：" + calendar.getTime());
System.out.println("LocalDateTime 转 LocalDate：" + localDateTime.toLocalDate());
System.out.println("LocalDate 转 LocalDateTime：" + localDate.atStartOfDay());
//通过此种转化可能会存在时区上的差异
System.out.println("LocalDateTime 转 Date：" + Date.from(localDateTime.toInstant(ZoneOffset.UTC)));
System.out.println("LocalDateTime 转 Date：" + Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant()));
//通过 Calendar 的 set 方法可以将 LocalDateTime 转为 Calendar
calendar.set(localDateTime.getYear(), (localDateTime.getMonthValue() - 1), localDateTime.getDayOfMonth(), localDateTime.getMinute(), localDateTime.getSecond());
System.out.println("LocalDateTime 转 Calendar：" + calendar.getTime());
}