Java8中的LocalDateTime和Date一些时间操作方法

先记录下jdk8之前的一些帮助方法

判断time是否在now的n天之内

/**
 * 判断time是否在now的n天之内
 * @param time
 * @param now
 * @param n 正数表示在条件时间n天之后，负数表示在条件时间n天之前
 * @return
 */
public static boolean belongDate(Date time, Date now, int n) {
 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
 Calendar calendar = Calendar.getInstance(); //得到日历
 calendar.setTime(now);//把当前时间赋给日历
 calendar.add(Calendar.DAY_OF_MONTH, n);
 Date before7days = calendar.getTime(); //得到n前的时间
 if (before7days.getTime() < time.getTime()) {
  return true;
 } else {
  return false;
 }
}

判断某个时间是否是在条件的起始时间与结束时间之内

/**
 * 判断time是否在from，to之内
 *
 * @param time 指定日期
 * @param from 开始日期
 * @param to 结束日期
 * @return
 */
public static boolean belongCalendar(Date time, Date from, Date to) {
 Calendar date = Calendar.getInstance();
 date.setTime(time);

Calendar after = Calendar.getInstance();
 after.setTime(from);

Calendar before = Calendar.getInstance();
 before.setTime(to);

if (date.after(after) && date.before(before)) {
  return true;
 } else {
  return false;
 }
}

判断给定时间与当前时间相差多少天

public static long getDistanceDays(String date) {
 DateFormat df = new SimpleDateFormat("yyyy-MM-dd");
 long days = 0;
 try {
  Date time = df.parse(date);//String转Date
  Date now = new Date();//获取当前时间
  long time1 = time.getTime();
  long time2 = now.getTime();
  long diff = time1 - time2;
  days = diff / (1000 * 60 * 60 * 24);
 } catch (Exception e) {
  e.printStackTrace();
 }
 return days;//正数表示在当前时间之后，负数表示在当前时间之前
}

将Date转换成String

private static final String LONG_PATTERN="yyyy-MM-dd HH:mm:ss";
private static final String SHORT_PATTERN="yyyy-MM-dd";

/**
 * 将日期转换为字符串
 */
public static String parse( Date d, String pattern){
 DateFormat df=null;
 if( pattern!=null && !"".equals(pattern) ){
  df=new SimpleDateFormat(pattern);
 }else{
  df=new SimpleDateFormat(LONG_PATTERN);
 }
 return df.format( d );
}

将String转换成Date

private static final String LONG_PATTERN="yyyy-MM-dd HH:mm:ss";
private static final String SHORT_PATTERN="yyyy-MM-dd";

/**
 * 将字符串转为日期
 */
public static Date parseStringToDate(String str, String pattern){
 DateFormat df = null;
 if( pattern!=null && !"".equals(pattern) ){
  df=new SimpleDateFormat( pattern );
 }else{
  df=new SimpleDateFormat( LONG_PATTERN );
 }
 Date d=null;
 try {
  d=df.parse(str);
 } catch (ParseException e) {
  e.printStackTrace();
 }
 return d;

}

获取指定年后的日期(例如三年后的日期)

Calendar date = Calendar.getInstance();
 date.setTime(new Date());
 date.add(Calendar.YEAR, +3);
 //倒计时结束后的时间
 Date scrap_year = date.getTime();
 System.out.println("三年后时间" + scrap_year);

Jdk8改革

LocalDateTime获取毫秒数

//获取秒数
Long second = LocalDateTime.now().toEpochSecond(ZoneOffset.of("+8"));
//获取毫秒数
Long milliSecond = LocalDateTime.now().toInstant(ZoneOffset.of("+8")).toEpochMilli();

LocalDateTime与String互转
//时间转字符串格式化
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyyMMddHHmmssSSS");
String dateTime = LocalDateTime.now(ZoneOffset.of("+8")).format(formatter);

//字符串转时间
String dateTimeStr = "2018-07-28 14:11:15";
DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime dateTime = LocalDateTime.parse(dateTimeStr, df);

Date与LocalDateTime互转

//将java.util.Date 转换为java8 的java.time.LocalDateTime,默认时区为东8区
public static LocalDateTime dateConvertToLocalDateTime(Date date) {
 return date.toInstant().atOffset(ZoneOffset.of("+8")).toLocalDateTime();
}

//将java8 的 java.time.LocalDateTime 转换为 java.util.Date，默认时区为东8区
public static Date localDateTimeConvertToDate(LocalDateTime localDateTime) {
 return Date.from(localDateTime.toInstant(ZoneOffset.of("+8")));
}

将LocalDateTime转为自定义的时间格式的字符串

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

将某时间字符串转为自定义时间格式的LocalDateTime

public static LocalDateTime parseStringToDateTime(String time, String format) {
DateTimeFormatter df = DateTimeFormatter.ofPattern(format);
return LocalDateTime.parse(time, df);
}

将long类型的timestamp转为LocalDateTime

public static LocalDateTime getDateTimeOfTimestamp(long timestamp) {
Instant instant = Instant.ofEpochMilli(timestamp);
ZoneId zone = ZoneId.systemDefault();
return LocalDateTime.ofInstant(instant, zone);
}

将LocalDateTime转为long类型的timestamp

public static long getTimestampOfDateTime(LocalDateTime localDateTime) {
ZoneId zone = ZoneId.systemDefault();
Instant instant = localDateTime.atZone(zone).toInstant();
return instant.toEpochMilli();
}

来源：https://blog.csdn.net/qq_36827957/article/details/90286149