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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