LocalDateTime小記

今天在使用LocalDateTime時需要將時間轉化使勁啊戳,原來我也沒怎麼用過.

發現又一個方法

    default long toEpochSecond(ZoneOffset offset) {
        Objects.requireNonNull(offset, "offset");
        long epochDay = toLocalDate().toEpochDay();
        long secs = epochDay * 86400 + toLocalTime().toSecondOfDay();
        secs -= offset.getTotalSeconds();
        return secs;
    }

這個方法需要傳入一個ZoneOffset的對象,經過查詢資料是這麼做的

    public static Long localDateTime2LongSecond(LocalDateTime localDateTime) {
        //獲得當前時區
        Instant instant = Instant.now();
        ZoneId systemZone = ZoneId.systemDefault();
        ZoneOffset currentOffsetForMyZone =  
        systemZone.getRules().getOffset(instant);
        return localDateTime.toEpochSecond(currentOffsetForMyZone);
    }

然而,我自己測試的時候發現該方法返回的時間戳和Date的時間戳有1000倍的出入

1570712734
1570712734225

發現LocalDateTime的toEpochSecond方法返回的單位是秒,而Date.getTime()返回的單位是毫秒.

源碼的註釋也有說明只是我給漏掉了,第一行就說了是seconds

    /**
     * Converts this date-time to the number of seconds from the epoch
     * of 1970-01-01T00:00:00Z.
     * <p>
     * This combines this local date-time and the specified offset to calculate the
     * epoch-second value, which is the number of elapsed seconds from 1970-01-01T00:00:00Z.
     * Instants on the time-line after the epoch are positive, earlier are negative.
     * <p>
     * This default implementation calculates from the epoch-day of the date and the
     * second-of-day of the time.
     *
     * @param offset  the offset to use for the conversion, not null
     * @return the number of seconds from the epoch of 1970-01-01T00:00:00Z
     */
    default long toEpochSecond(ZoneOffset offset) {
        Objects.requireNonNull(offset, "offset");
        long epochDay = toLocalDate().toEpochDay();
        long secs = epochDay * 86400 + toLocalTime().toSecondOfDay();
        secs -= offset.getTotalSeconds();
        return secs;
    }

真正的實現方式是

/**
     * @description: 有LocalDateTime轉換成時間戳(毫秒 ）
     * @param: [localDateTime]
     * @return: java.lang.Long
     * @author: lky
     * @date: 2019/10/10 09:57
     */
    public static Long localDateTime2Long(LocalDateTime localDateTime) {
        //獲得當前時區
        Instant instant = Instant.now();
        ZoneId systemZone = ZoneId.systemDefault();
        ZoneOffset currentOffsetForMyZone = systemZone.getRules().getOffset(instant);
        return localDateTime.atZone(currentOffsetForMyZone).toInstant().toEpochMilli();
    }

另送時間戳轉換爲LocalDateTime的方法,*1000的操作是爲了將(秒)轉換爲毫秒 ,請忽略

/**
     * @description: 將Long類型的時間戳轉換爲LocalDateTime類型
     * @param: [timestamp]
     * @return: java.time.LocalDateTime
     * @author: lky
     * @date: 2019/10/9 11:08
     */
    public static LocalDateTime getDateTimeOfTimestamp(long timestamp) {
        if ((timestamp + "").length() < 13) {
            timestamp *= 1000;
        }
        Instant instant = Instant.ofEpochMilli(timestamp);
        ZoneId zone = ZoneId.systemDefault();
        return LocalDateTime.ofInstant(instant, zone);
    }