【Java】 日付・時間 について ～ Java8編 ～

Java

 ■ 日付 / 時間 / 日時 Java8版

 * java.time.LocalDateTime
 * java.time.LocalDate
 * java.time.LocalTime

 フォーマッタ 

 * java.time.fomat.DateTimeFormatter

 ■ 日付 / 時間 / 日時あれこれ

 加算/減算 

 * plusXxxx() の戻り値から取得する

サンプル 

DateTimeFormatter datetimeFormatter = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
LocalDateTime currenyDateTime = LocalDateTime.now();

// ★注目★
LocalDateTime plusHourDateTime = currenyDateTime.plusHours(2L);
LocalDateTime minusHourDateTime = currenyDateTime.plusHours(-2L);

System.out.println(currenyDateTime.format(datetimeFormatter));
System.out.println(plusHourDateTime.format(datetimeFormatter));
System.out.println(minusHourDateTime.format(datetimeFormatter));

出力結果 

2018/03/26 22:19:10
2018/03/27 00:19:10
2018/03/26 20:19:10

 ■ サンプル

import java.text.SimpleDateFormat;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;
import java.util.Date;

public class Main {

  public static void main(String[] args) {
    DateTimeFormatter datetimeFormatter = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");

    // 現在日時
    LocalDateTime currenyDateTime = LocalDateTime.now();
    System.out.println(currenyDateTime.format(datetimeFormatter));

    // 内部にLocalDateとLocalTimeのインスタンスを持っている
    LocalDate currenyDate = currenyDateTime.toLocalDate();
    LocalTime currenyTime = currenyDateTime.toLocalTime();

    DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("yyyy/MM/dd");
    System.out.println(currenyDate.format(dateFormatter));
    DateTimeFormatter timeFormatter = DateTimeFormatter.ofPattern("HH:mm:ss");
    System.out.println(currenyTime.format(timeFormatter));

    LocalDateTime targetDateTime1 = LocalDateTime.of(2018, 2, 24, 12, 11, 59);
    System.out.println(targetDateTime1.format(datetimeFormatter));
    LocalDateTime targetDateTime2 = LocalDateTime.of(2018, 2, 24, 2, 13, 32, 0);
    System.out.println(targetDateTime2.format(datetimeFormatter));

    LocalDateTime targetDateTime3 = LocalDateTime.parse("2018/02/24 01:10:19", datetimeFormatter);
    System.out.println(targetDateTime3.format(datetimeFormatter));

    try {
      LocalDateTime targetDateTimeError = LocalDateTime.parse("2018/2/24 1:10:19", datetimeFormatter);
      System.out.println(targetDateTimeError.format(datetimeFormatter));
    } catch (Exception ex) {
      ex.printStackTrace();
    }

    DateTimeFormatter datetimeFormatterEx = DateTimeFormatter.ofPattern("yyyy/[]M/[]d []H:[]m:[]s");
    LocalDateTime targetDateTimeOK = LocalDateTime.parse("2018/2/24 1:10:9", datetimeFormatterEx);
    System.out.println(targetDateTimeOK.format(datetimeFormatterEx));

    // LocalDateTime -> Date
    LocalDateTime targetDate = LocalDateTime.of(2018, 2, 24, 12, 11, 59);
    Date date = Date.from(targetDate.atZone(ZoneId.systemDefault()).toInstant());

    try {
      SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
      System.out.println(simpleDateFormat.format(date));
    } catch (Exception ex) {
      ex.printStackTrace();
    }

    // Date -> LocalDateTime
    LocalDateTime localDateTime = LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault());
    System.out.println(localDateTime.format(datetimeFormatter));
  }
}

 出力結果 

2018/02/24 01:55:53
2018/02/24
01:55:53
2018/02/24 12:11:59
2018/02/24 02:13:32
2018/02/24 01:10:19
java.time.format.DateTimeParseException: Text '2018/2/24 1:10:19' could not be parsed at index 5
    at java.time.format.DateTimeFormatter.parseResolved0(Unknown Source)
    at java.time.format.DateTimeFormatter.parse(Unknown Source)
    at java.time.LocalDateTime.parse(Unknown Source)
    at com.sample.datetime.Main.main(Main.java:39)
2018/2/24 1:10:9
2018-02-24 12:11:59
2018/02/24 12:11:59

 ■ 注意

 * 決まった形式ではない文字を使用してDateTimeFormatterにかけると
  「IllegalArgumentException: Unknown pattern letter」で怒られる。

 ダメな例 

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

public class Main {
  public static void main(String[] args) {
    // ★「hello_world_yyyyMMdd_HHmmss.csv」の部分★
    DateTimeFormatter datetimeFormatter = DateTimeFormatter.ofPattern("hello_world_yyyyMMdd_HHmmss.csv");
    LocalDateTime currenyDateTime = LocalDateTime.now();
    System.out.println(currenyDateTime.format(datetimeFormatter));
  }
}

 エラー結果 

Exception in thread "main" java.lang.IllegalArgumentException: Unknown pattern letter: l
    at java.time.format.DateTimeFormatterBuilder.parsePattern(Unknown Source)
    at java.time.format.DateTimeFormatterBuilder.appendPattern(Unknown Source)
    at java.time.format.DateTimeFormatter.ofPattern(Unknown Source)
    at com.sample.date.Main.main(Main.java:9)

 参考文献

https://qiita.com/tag1216/items/91a471b33f383981bfaa
http://blog.y-yuki.net/entry/2016/09/15/003000
http://news.mynavi.jp/special/2014/java8/008.html
http://www.atmarkit.co.jp/ait/articles/1412/16/news041_3.html
パースエラー
https://qiita.com/ricoirico/items/ec6be9cd9f7ce6e88e8d

 関連記事

日付・時間 について ～ 入門編 ～ https://dk521123.hatenablog.com/entry/2014/11/18/235600
日付・時間 について ～ 基本編 ～
https://dk521123.hatenablog.com/entry/2016/10/12/235711
日付・時間 について ～ System.currentTimeMillis / System.nanoTime ～
https://dk521123.hatenablog.com/entry/2017/04/25/223122