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();
}

总结

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