【README】

1）本文總結(jié)了java8中日期時間常用工具方法；包括：

• 日期時間對象格式化為字符串；
• 日期時間字符串解析為日期時間對象；
• 日期時間對象轉(zhuǎn)換；
  • 轉(zhuǎn)換過程中，需要注意的是： Instant與Date帶時區(qū)（易變），而LocalDateTime，LocalDate，LocalTime 不帶時區(qū)（不可變）；

2）日期時間工具類定義如下：

public class BusiDateTimeUtils {/** 日期時間格式化器 */private static final DateTimeFormatter DATETIME_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");/** 日期格式化器 */private static final DateTimeFormatter DATE_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd");private BusiDateTimeUtils() {// do nothing.}
// .................... 
}

?

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【1】當(dāng)前日期時間操作

/** -------------------- 1. 當(dāng)前日期時間操作 -------------------- */public static String getNowLocalDateTimeStr() {return LocalDateTime.now().format(DATETIME_FORMATTER);}public static String getNowLocalDateStr() {return LocalDate.now().format(DATE_FORMATTER);}

【1.1】單測案例：

/** -------------------- 1. 當(dāng)前日期時間操作 -------------------- */@Testpublic void test1() {// 獲取當(dāng)前日期時間String nowLocalDateTimeStr = BusiDateTimeUtils.getNowLocalDateTimeStr();System.out.println("nowLocalDateTimeStr="+nowLocalDateTimeStr); // 2023-10-05 21:28:09// 獲取當(dāng)前日期String nowLocalDateStr = BusiDateTimeUtils.getNowLocalDateStr();System.out.println("nowLocalDateStr=" + nowLocalDateStr); // 2023-10-05}

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【2】字符串解析為日期時間對象

 /** -------------------- 2. 字符串解析為日期時間對象 -------------------- */public static LocalDateTime parseLocalDateTime(String dateTimeStr) {return LocalDateTime.parse(dateTimeStr, DATETIME_FORMATTER);}public static LocalDate parseLocalDate(String dateStr) {return LocalDate.parse(dateStr, DATE_FORMATTER);}

【2.1】單測案例

/** -------------------- 2. 字符串解析為日期時間對象 -------------------- */@Testpublic void test2() {// 解析當(dāng)前日期時間String nowLocalDateTimeStr = BusiDateTimeUtils.getNowLocalDateTimeStr();System.out.println("nowLocalDateTimeStr="+ nowLocalDateTimeStr); // 2023-10-05 21:29:32LocalDateTime parsedLocalDateTime = BusiDateTimeUtils.parseLocalDateTime(nowLocalDateTimeStr);System.out.println(parsedLocalDateTime); // 2023-10-05T21:29:32// 解析當(dāng)前日期String nowLocalDateStr = BusiDateTimeUtils.getNowLocalDateStr();System.out.println("nowLocalDateStr=" + nowLocalDateStr); // 2023-10-05LocalDate parsedLocalDate = BusiDateTimeUtils.parseLocalDate(nowLocalDateStr);System.out.println(parsedLocalDate); // 2023-10-05}

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【3】日期時間對象格式化為字符串

/** -------------------- 3. 日期時間對象格式化為字符串 -------------------- */public static String format(LocalDateTime localDateTime) {return localDateTime.format(DATETIME_FORMATTER);}public static String format(LocalDate localDate) {return localDate.format(DATE_FORMATTER);}

【3.1】單測案例

/** -------------------- 3. 日期時間對象格式化為字符串 -------------------- */@Testpublic void test3() {// 格式化當(dāng)前日期時間對象為字符串String nowLocalDateTimeStr = BusiDateTimeUtils.getNowLocalDateTimeStr();System.out.println("nowLocalDateTimeStr="+ nowLocalDateTimeStr); // 2023-10-05 21:35:19LocalDateTime parsedLocalDateTime = BusiDateTimeUtils.parseLocalDateTime(nowLocalDateTimeStr);String formatedLocalDateTime = BusiDateTimeUtils.format(parsedLocalDateTime);System.out.println(formatedLocalDateTime); // 2023-10-05 21:35:19// 格式化當(dāng)前日期對象為字符串String nowLocalDateStr = BusiDateTimeUtils.getNowLocalDateStr();System.out.println("nowLocalDateStr=" + nowLocalDateStr); // 2023-10-05LocalDate parsedLocalDate = BusiDateTimeUtils.parseLocalDate(nowLocalDateStr);String formatedLocalDate = BusiDateTimeUtils.format(parsedLocalDate);System.out.println(formatedLocalDate); // 2023-10-05}

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【4】*LocalDateTime 轉(zhuǎn)為其他日期時間類型（重要）

/** -------------------- 4. LocalDateTime 轉(zhuǎn)為其他日期時間類型 -------------------- */public static LocalDate toLocalDate(LocalDateTime localDateTime) {return localDateTime.toLocalDate();}public static Instant toInstant(LocalDateTime localDateTime) {return localDateTime.toInstant(ZoneOffset.UTC);}public static Date toDate(LocalDateTime localDateTime) {return Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant());}

【說明】LocalDateTime 轉(zhuǎn) Instant與Date時，做了一些特殊處理：

• LocalDateTime沒有時區(qū)，而Instant有時區(qū)；為了統(tǒng)一，把Instant的時區(qū)設(shè)置為0時區(qū)（UTC），則LocalDateTime與Instant都沒有時區(qū)了；
• LocalDateTime沒有時區(qū)，Instant有時區(qū)，Date有時區(qū)：
  • 先把 LocalDateTime轉(zhuǎn)為帶時區(qū)的日期時間 ZonedDateTime；
  • 再把 ZonedDateTime 轉(zhuǎn) Instant（默認(rèn)時區(qū)為系統(tǒng)時區(qū)）；
  • 最后把Instant轉(zhuǎn)Date（默認(rèn)時區(qū)為系統(tǒng)時區(qū)）；?

【4.1】單測案例

/** -------------------- 4. LocalDateTime 轉(zhuǎn)為其他日期時間類型 -------------------- */@Testpublic void test4() {LocalDateTime nowLocalDateTime = LocalDateTime.now();System.out.println("nowLocalDateTimeStr="+BusiDateTimeUtils.format(nowLocalDateTime)); // 2023-10-05 21:37:14// LocalDateTime 轉(zhuǎn) LocalDateLocalDate localDate = BusiDateTimeUtils.toLocalDate(nowLocalDateTime);LocalDate localDate2 = nowLocalDateTime.toLocalDate(); // 與上一行代碼效果一樣System.out.println("localDate=" + localDate); // 2023-10-05// LocalDateTime 轉(zhuǎn) InstantInstant nowInstant = BusiDateTimeUtils.toInstant(nowLocalDateTime);System.out.println(nowInstant); // 2023-10-05T21:37:14.677Z// LocalDateTime 轉(zhuǎn) DateDate nowDate = BusiDateTimeUtils.toDate(nowLocalDateTime);System.out.println(nowDate); // Thu Oct 05 21:37:14 CST 2023 }

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【5】LocalDate 轉(zhuǎn)為其他日期時間類型

/** -------------------- 5. LocalDate 轉(zhuǎn)為其他日期時間類型 -------------------- */public static LocalDateTime toLocalDateTime(LocalDate localDate) {return localDate.atStartOfDay();}public static Instant toInstant(LocalDate localDate) {return localDate.atStartOfDay().toInstant(ZoneOffset.UTC);}public static Date toDate(LocalDate localDate) {return Date.from(localDate.atStartOfDay().atZone(ZoneId.systemDefault()).toInstant());}

【說明】LocalDate 轉(zhuǎn) Instant與Date時，做了一些特殊處理：與 LocalDateTime 轉(zhuǎn) Instant與Date類似 ，這里不再贅述；參見本文章節(jié)【4】；

【5.1】單測案例

/** -------------------- 5. LocalDate 轉(zhuǎn)為其他日期時間類型 -------------------- */@Testpublic void test5() {LocalDate nowLocalDate = LocalDate.now();System.out.println("nowLocalDateStr="+BusiDateTimeUtils.format(nowLocalDate)); // 2023-10-05// LocalDate 轉(zhuǎn) LocalDateTimeLocalDateTime localDateTime = BusiDateTimeUtils.toLocalDateTime(nowLocalDate);System.out.println("localDateTime=" + localDateTime); // 2023-10-05T00:00// LocalDate 轉(zhuǎn) InstantInstant nowInstant = BusiDateTimeUtils.toInstant(nowLocalDate);System.out.println(nowInstant); // 2023-10-05T00:00// LocalDate 轉(zhuǎn) DateDate nowDate = BusiDateTimeUtils.toDate(nowLocalDate);System.out.println(nowDate); //  Thu Oct 05 00:00:00 CST 2023}

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【6】Instant 轉(zhuǎn)為其他日期時間類型

/** -------------------- 6. Instant 轉(zhuǎn)為其他日期時間類型 -------------------- */public static LocalDateTime toLocalDateTime(Instant instantWithoutZone) {return LocalDateTime.ofInstant(instantWithoutZone, ZoneOffset.UTC);}public static LocalDate toLocalDate(Instant instantWithoutZone) {return toLocalDateTime(instantWithoutZone).toLocalDate();}public static Date toDate(Instant instantWithoutZone) {return toDate(toLocalDateTime(instantWithoutZone));}

【說明】

注意上述工具方法中入?yún)?Instant變量是不帶時區(qū)的，也可以理解為時區(qū)為UTC（0時區(qū)）；

【6.1】單測案例

/** -------------------- 6. Instant 轉(zhuǎn)為其他日期時間類型 -------------------- */@Testpublic void test6() {Instant nowInstantWithoutZone = LocalDateTime.now().toInstant(ZoneOffset.UTC);System.out.println("nowZonedInstant="+nowInstantWithoutZone); // 2023-10-05T22:00:54.783ZSystem.out.println("Instant.now()=" + Instant.now()); // 2023-10-05T14:00:54.798Z(注意這里晚了8個小時)// Instant 轉(zhuǎn) LocalDateTimeLocalDateTime localDateTime = BusiDateTimeUtils.toLocalDateTime(nowInstantWithoutZone);System.out.println("localDateTime=" + localDateTime); // 2023-10-05T22:00:54.783// Instant 轉(zhuǎn) LocalDateLocalDate localDate = BusiDateTimeUtils.toLocalDate(nowInstantWithoutZone);System.out.println("localDate=" + localDate); // 2023-10-05// Instant 轉(zhuǎn) DateDate date = BusiDateTimeUtils.toDate(nowInstantWithoutZone);System.out.println("date=" + date); // date=Thu Oct 05 22:00:54 CST 2023 }

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【7】總結(jié)

【7.1】日期時間工具類

/*** @Description 日期時間工具類* @author xiao tang* @version 1.0.0* @createTime 2023年10月05日*/
public class BusiDateTimeUtils {/** 日期時間格式化器 */private static final DateTimeFormatter DATETIME_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");/** 日期格式化器 */private static final DateTimeFormatter DATE_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd");private BusiDateTimeUtils() {// do nothing.}/** -------------------- 1. 當(dāng)前日期時間操作 -------------------- */public static String getNowLocalDateTimeStr() {return LocalDateTime.now().format(DATETIME_FORMATTER);}public static String getNowLocalDateStr() {return LocalDate.now().format(DATE_FORMATTER);}/** -------------------- 2. 字符串解析為日期時間對象 -------------------- */public static LocalDateTime parseLocalDateTime(String dateTimeStr) {return LocalDateTime.parse(dateTimeStr, DATETIME_FORMATTER);}public static LocalDate parseLocalDate(String dateStr) {return LocalDate.parse(dateStr, DATE_FORMATTER);}/** -------------------- 3. 日期時間對象格式化為字符串 -------------------- */public static String format(LocalDateTime localDateTime) {return localDateTime.format(DATETIME_FORMATTER);}public static String format(LocalDate localDate) {return localDate.format(DATE_FORMATTER);}/** -------------------- 4. LocalDateTime 轉(zhuǎn)為其他日期時間類型 -------------------- */public static LocalDate toLocalDate(LocalDateTime localDateTime) {return localDateTime.toLocalDate();}public static Instant toInstant(LocalDateTime localDateTime) {return localDateTime.toInstant(ZoneOffset.UTC);}public static Date toDate(LocalDateTime localDateTime) {return Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant());}/** -------------------- 5. LocalDate 轉(zhuǎn)為其他日期時間類型 -------------------- */public static LocalDateTime toLocalDateTime(LocalDate localDate) {return localDate.atStartOfDay();}public static Instant toInstant(LocalDate localDate) {return localDate.atStartOfDay().toInstant(ZoneOffset.UTC);}public static Date toDate(LocalDate localDate) {return Date.from(localDate.atStartOfDay().atZone(ZoneId.systemDefault()).toInstant());}/** -------------------- 6. Instant 轉(zhuǎn)為其他日期時間類型 -------------------- */public static LocalDateTime toLocalDateTime(Instant instantWithoutZone) {return LocalDateTime.ofInstant(instantWithoutZone, ZoneOffset.UTC);}public static LocalDate toLocalDate(Instant instantWithoutZone) {return toLocalDateTime(instantWithoutZone).toLocalDate();}public static Date toDate(Instant instantWithoutZone) {return toDate(toLocalDateTime(instantWithoutZone));}
}

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【7.2】日期時間工具類單測案例

/*** @Description 日期時間工具類單測案例 * @author xiao tang* @version 1.0.0* @createTime 2023年10月05日*/
public class BusiDateTimeUtilsTest {/** -------------------- 1. 當(dāng)前日期時間操作 -------------------- */@Testpublic void test1() {// 獲取當(dāng)前日期時間String nowLocalDateTimeStr = BusiDateTimeUtils.getNowLocalDateTimeStr();System.out.println("nowLocalDateTimeStr="+nowLocalDateTimeStr); // 2023-10-05 21:28:09// 獲取當(dāng)前日期String nowLocalDateStr = BusiDateTimeUtils.getNowLocalDateStr();System.out.println("nowLocalDateStr=" + nowLocalDateStr); // 2023-10-05}/** -------------------- 2. 字符串解析為日期時間對象 -------------------- */@Testpublic void test2() {// 解析當(dāng)前日期時間String nowLocalDateTimeStr = BusiDateTimeUtils.getNowLocalDateTimeStr();System.out.println("nowLocalDateTimeStr="+ nowLocalDateTimeStr); // 2023-10-05 21:29:32LocalDateTime parsedLocalDateTime = BusiDateTimeUtils.parseLocalDateTime(nowLocalDateTimeStr);System.out.println(parsedLocalDateTime); // 2023-10-05T21:29:32// 解析當(dāng)前日期String nowLocalDateStr = BusiDateTimeUtils.getNowLocalDateStr();System.out.println("nowLocalDateStr=" + nowLocalDateStr); // 2023-10-05LocalDate parsedLocalDate = BusiDateTimeUtils.parseLocalDate(nowLocalDateStr);System.out.println(parsedLocalDate); // 2023-10-05}/** -------------------- 3. 日期時間對象格式化為字符串 -------------------- */@Testpublic void test3() {// 格式化當(dāng)前日期時間對象為字符串String nowLocalDateTimeStr = BusiDateTimeUtils.getNowLocalDateTimeStr();System.out.println("nowLocalDateTimeStr="+ nowLocalDateTimeStr); // 2023-10-05 21:35:19LocalDateTime parsedLocalDateTime = BusiDateTimeUtils.parseLocalDateTime(nowLocalDateTimeStr);String formatedLocalDateTime = BusiDateTimeUtils.format(parsedLocalDateTime);System.out.println(formatedLocalDateTime); // 2023-10-05 21:35:19// 格式化當(dāng)前日期對象為字符串String nowLocalDateStr = BusiDateTimeUtils.getNowLocalDateStr();System.out.println("nowLocalDateStr=" + nowLocalDateStr); // 2023-10-05LocalDate parsedLocalDate = BusiDateTimeUtils.parseLocalDate(nowLocalDateStr);String formatedLocalDate = BusiDateTimeUtils.format(parsedLocalDate);System.out.println(formatedLocalDate); // 2023-10-05}/** -------------------- 4. LocalDateTime 轉(zhuǎn)為其他日期時間類型 -------------------- */@Testpublic void test4() {LocalDateTime nowLocalDateTime = LocalDateTime.now();System.out.println("nowLocalDateTimeStr="+BusiDateTimeUtils.format(nowLocalDateTime)); // 2023-10-05 21:37:14// LocalDateTime 轉(zhuǎn) LocalDateLocalDate localDate = BusiDateTimeUtils.toLocalDate(nowLocalDateTime);LocalDate localDate2 = nowLocalDateTime.toLocalDate(); // 與上一行代碼效果一樣System.out.println("localDate=" + localDate); // 2023-10-05// LocalDateTime 轉(zhuǎn) InstantInstant nowInstant = BusiDateTimeUtils.toInstant(nowLocalDateTime);System.out.println(nowInstant); // 2023-10-05T21:37:14.677Z// LocalDateTime 轉(zhuǎn) DateDate nowDate = BusiDateTimeUtils.toDate(nowLocalDateTime);System.out.println(nowDate); // Thu Oct 05 21:37:14 CST 2023}/** -------------------- 5. LocalDate 轉(zhuǎn)為其他日期時間類型 -------------------- */@Testpublic void test5() {LocalDate nowLocalDate = LocalDate.now();System.out.println("nowLocalDateStr="+BusiDateTimeUtils.format(nowLocalDate)); // 2023-10-05// LocalDate 轉(zhuǎn) LocalDateTimeLocalDateTime localDateTime = BusiDateTimeUtils.toLocalDateTime(nowLocalDate);System.out.println("localDateTime=" + localDateTime); // 2023-10-05T00:00// LocalDate 轉(zhuǎn) InstantInstant nowInstant = BusiDateTimeUtils.toInstant(nowLocalDate);System.out.println(nowInstant); // 2023-10-05T00:00// LocalDate 轉(zhuǎn) DateDate nowDate = BusiDateTimeUtils.toDate(nowLocalDate);System.out.println(nowDate); //  Thu Oct 05 00:00:00 CST 2023}/** -------------------- 6. Instant 轉(zhuǎn)為其他日期時間類型 -------------------- */@Testpublic void test6() {Instant nowInstantWithoutZone = LocalDateTime.now().toInstant(ZoneOffset.UTC);System.out.println("nowZonedInstant="+nowInstantWithoutZone); // 2023-10-05T22:00:54.783ZSystem.out.println("Instant.now()=" + Instant.now()); // 2023-10-05T14:00:54.798Z(注意這里晚了8個小時)// Instant 轉(zhuǎn) LocalDateTimeLocalDateTime localDateTime = BusiDateTimeUtils.toLocalDateTime(nowInstantWithoutZone);System.out.println("localDateTime=" + localDateTime); // 2023-10-05T22:00:54.783// Instant 轉(zhuǎn) LocalDateLocalDate localDate = BusiDateTimeUtils.toLocalDate(nowInstantWithoutZone);System.out.println("localDate=" + localDate); // 2023-10-05// Instant 轉(zhuǎn) DateDate date = BusiDateTimeUtils.toDate(nowInstantWithoutZone);System.out.println("date=" + date); // date=Thu Oct 05 22:00:54 CST 2023}
}