Java日期时间操作基础——包含JDK1.8时间操作新特性 Java日期时间操作基础—

JDK1.7日期时间操作
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示例小结

public class DateTest {public static final String FORMAT_DATE = "yyyy-MM-dd"; public static final String FORMAT = "yyyy-MM-dd HH:mm:ss"; public static final String FORMAT_MIN = "yyyy-MM-dd HH:mm"; public static final String FORMAT_MILLISECOND = "yyyy-MM-dd HH:mm:ss.S"; private static String[] parsePatterns = {"yyyy-MM-dd", "yyyy-MM-dd HH:mm:ss", "yyyy-MM-dd HH:mm", "yyyy/MM/dd", "yyyy/MM/dd HH:mm:ss", "yyyy/MM/dd HH:mm"}; /** * SimpleDateFormat时间格式化 */ @Test public void test1() throws ParseException { Date date = new Date(); /** *常用格式： * yyyy-MM-dd * yyyy-MM-dd HH:mm:ss *yyyy-MM-dd HH:mm */ //根据约定好的pattern时间格式进行格式化和解析 SimpleDateFormat dateFormat = new SimpleDateFormat(FORMAT); //格式化 String dateStr = dateFormat.format(date); System.out.println(dateStr); //字符串解析成date对象 Date parseDate = dateFormat.parse(dateStr); System.out.println(parseDate); } /** * 2021-12-04 00:49:39 * Sat Dec 04 00:49:39 CST 2021 *//** * Calendar（抽象类）日历类的使用 */ @Test public void test2() { //两种创建 //Calendar calendar = new GregorianCalendar(); //默认用getInstance()创建 Calendar calendar = Calendar.getInstance(); //get() //根据日历类型获取数据 //当天日历对应的一个月的第几天 int day = calendar.get(Calendar.DAY_OF_MONTH); System.out.println(day); //set() 设置日期 calendar.set(Calendar.DAY_OF_MONTH, 9); day = calendar.get(Calendar.DAY_OF_MONTH); System.out.println(day); //添加天数，负数表示减天数 calendar.add(Calendar.DAY_OF_MONTH, -1); day = calendar.get(Calendar.DAY_OF_MONTH); System.out.println(day); //getTime() 日历类转Date Date date = calendar.getTime(); System.out.println(date); //根据Date日期设置日历 calendar.setTime(new Date()); day = calendar.get(Calendar.DAY_OF_MONTH); System.out.println(day); } /** * 4 * 9 * 8 * Wed Dec 08 01:55:33 CST 2021 * 4 */}

JDK1.8日期时间操作——重点 LocalDateTime

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示例小结

public class JDKDateTest {@Test public void test1() { //创建日期对象 //获取当前日期时间 now() LocalDate localDate = LocalDate.now(); LocalTime localTime = LocalTime.now(); LocalDateTime localDateTime = LocalDateTime.now(); System.out.println(localDate); System.out.println(localTime); System.out.println(localDateTime); //2021-12-04 //23:44:44.112 //2021-12-04T23:44:44.112 //创建指定日期时间的of()方法 LocalDateTime dateTime = LocalDateTime.of(2020, 10, 10, 12, 12, 12); LocalDate date = LocalDate.of(2020, 10, 10); LocalTime time = LocalTime.of(12, 12, 12); System.out.println(dateTime); System.out.println(date); System.out.println(time); //2020-10-10T12:12:12 //2020-10-10 //12:12:12 //getXXX方法获取时间里的年月日的值相关的属性 int dayOfYear = dateTime.getDayOfYear(); Month month = dateTime.getMonth(); int monthValue = https://www.it610.com/article/dateTime.getMonthValue(); int dayOfMonth = dateTime.getDayOfMonth(); System.out.println(dayOfYear); System.out.println(month); System.out.println(monthValue); System.out.println(dayOfMonth); //284 //OCTOBER //10 //10 //withXXX() 设置指定的时间相关的属性返回新的日期，原来的日期是不变的 //LocalDateTime JDK时间不可变性，因此是线程安全的。 LocalDateTime withDateTime1 = dateTime.with(localDateTime); LocalDateTime withDateTime2 = dateTime.withDayOfMonth(11); System.out.println("原来日期："+dateTime); System.out.println("修改后日期1："+withDateTime1); System.out.println("修改后日期2："+withDateTime2); System.out.println("-----------------------------------"); //原来日期：2020-10-10T12:12:12 //修改后日期1：2021-12-04T23:44:44.112 //修改后日期2：2020-10-11T12:12:12 //日期时间的添加删除 //可以直接添加想要添加的天数或其他属性值，返回的日期时间会自动处理为对应的日期时间 LocalDateTime plusDateTime = dateTime.plusDays(60); LocalDateTime plusDateTime2 = dateTime.plusHours(70); //加减时间都可以操作负数，负数对应就是相反的操作，没有问题 LocalDateTime minusDateTime1 = dateTime.minusDays(-1); System.out.println("原来日期："+dateTime); System.out.println(plusDateTime); System.out.println(plusDateTime2); System.out.println(minusDateTime1); //原来日期：2020-10-10T12:12:12 //2020-12-09T12:12:12 //2020-10-13T10:12:12 //2020-10-11T12:12:12 } }

Instant——瞬时——类似于Date

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示例小结

public class InstantTest {@Test public void test1() { //获取本初子午线对应的当前时间 Instant instant = Instant.now(); long timeMillis = System.currentTimeMillis(); System.out.println(instant); //2021-12-04T16:16:27.593Z //添加东八区时间的偏移量 OffsetDateTime offsetDateTime = instant.atOffset(ZoneOffset.ofHours(8)); System.out.println(offsetDateTime); //2021-12-05T00:16:27.593+08:00 //获取19701-1-1 00:00:00到现在的毫秒数，类似于System.currentTimeMillis() long epochMilli = instant.toEpochMilli(); System.out.println("toEpochMilli "+epochMilli); System.out.println("currentTimeMillis "+timeMillis); //toEpochMilli 1638634587593 //currentTimeMillis 1638634587593 //根据时间戳获取Instant示例，类似于Date(long date) Instant instant1 = Instant.ofEpochMilli(epochMilli); System.out.println(instant1); //2021-12-04T16:16:27.593Z } }

DateTimeFormatter——格式化解析
时间格式化注意

yyyy-MM-dd HH:mm:ss HH表示24小时时间制 yyyy-MM-dd hh:mm:ss HH表示12小时时间制

代码示例

@Test public void test2(){ LocalDateTime now = LocalDateTime.now(); //自定义格式化类型ofPattern() DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"); //格式化 String nowStr = formatter.format(now); System.out.println(nowStr); //2021-12-05 00:49:37 //解析 LocalDateTime dateTime = LocalDateTime.parse(nowStr, formatter); System.out.println(dateTime); //2021-12-05T00:49:37 TemporalAccessor parse1 = formatter.parse(nowStr); System.out.println(parse1); //{},ISO resolved to 2021-12-05T00:49:37 //强转报错，要使用LocalDateTime.parse(nowStr, formatter); //java.lang.ClassCastException: java.time.format.Parsed cannot be cast to java.time.LocalDateTime //LocalDateTime parse2 = (LocalDateTime) formatter.parse(nowStr); //System.out.println(parse2); }