文章目錄

• Pre
• 模擬SimpleDateFormate線程安全問題
• LocalDate
• LocalTime
• LocalDateTime
• Instant
• Period
• Duration
• format
• parse

Pre

并發編程-12線程安全策略之常見的線程不安全類

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模擬SimpleDateFormate線程安全問題

package com.artisan.java8.testDate;import java.text.ParseException; import java.text.SimpleDateFormat; import java.time.*; import java.time.format.DateTimeFormatter; import java.time.temporal.ChronoField; import java.util.Date;/*** @author 小工匠* @version 1.0* @description: TODO* @date 2021/3/5 0:22* @mark: show me the code , change the world*/ public class DateInJava8 {public static void main(String[] args) throws ParseException, InterruptedException {Date date = new Date();System.out.println(date);/*** 模擬SimpleDateFormat 的線程安全問題** Exception in thread "Thread-30" java.lang.NumberFormatException: multiple points** Exception in thread "Thread-24" java.lang.NumberFormatException: For input string: "E.250214E4"**/SimpleDateFormat sdf = new SimpleDateFormat("YYYY-MM-dd");for (int i = 0; i < 100; i++) {new Thread(() -> {for (int j = 0; j < 20; j++) {try {String format = sdf.format(date);Date d = sdf.parse(format);System.out.println(d);} catch (ParseException e) {e.printStackTrace();}}}).start();}}}

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LocalDate

https://nowjava.com/docs/java-api-11/java.base/java/time/LocalDate.html

LocalDate 是final修飾的不可變類 并且是線程安全的.

• Java LocalDate is immutable class and hence thread safe.

• LocalDate provides date output in the format of YYYY-MM-dd.
  

• The LocalDate class has no time or Timezone data. So LocalDate is suitable to represent dates such as Birthday, National Holiday etc.

• LocalDate class implements Temporal, TemporalAdjuster, ChronoLocalDate and Serializable interfaces.

• LocalDate is a final class, so we can’t extend it.

• LocalDate is a value based class, so we should use equals() method for comparing if two LocalDate instances are equal or not.

public static void testLocalDate(){LocalDate x = LocalDate.now(); // 日期 2021-03-05System.out.println(x);LocalDate lo = LocalDate.of(2021,3,5);System.out.println(lo.getYear()); // 年 2021System.out.println(lo.getMonth()); // 月 MARCHSystem.out.println(lo.getDayOfMonth()); // 日 5System.out.println(lo.getDayOfYear()); // 一年中的第幾天System.out.println(lo.getDayOfMonth());// 一個月中的第幾天System.out.println(lo.getDayOfWeek());// 禮拜幾System.out.println(lo.get(ChronoField.DAY_OF_MONTH));}

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LocalTime

• LocalTime provides time without any time zone information. It is very much similar to observing the time from a wall clock which just shown the time and not the time zone information.

• The assumption from this API is that all the calendar system uses the same way of representing the time.

• It is a value-based class, so use of reference equality (==), identity hash code or synchronization on instances of LocalTime may have - unexpected results and is highly advised to be avoided. The equals method should be used for comparisons.

• The LocalTime class is immutable that mean any operation on the object would result in a new instance of LocalTime reference.

private static void testLocalTime() {LocalTime time = LocalTime.now();System.out.println(time.getHour());System.out.println(time.getMinute());System.out.println(time.getSecond());}

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LocalDateTime

• Java LocalDateTime is an immutable class, so it’s thread safe and suitable to use in multithreaded environment.

• LocalDateTime provides date and time output in the format of YYYY-MM-DD-hh-mm-ss.zzz, extendable to nanosecond precision. So we can store “2017-11-10 21:30:45.123456789” in LocalDateTime object.
  

• Just like the LocalDate class, LocalDateTime has no time zone data. We can use LocalDateTime instance for general purpose date and time information.

• LocalDateTime class implements Comparable, ChronoLocalDateTime, Temporal, TemporalAdjuster, TermporalAccessor and Serializable interfaces.

• LocalDateTime is a final class, so we can’t extend it.

• LocalDateTime is a value based class, so we should use equals() method to check if two instances of LocalDateTime are equal or not.

• LocalDateTime class is a synergistic ‘combination’ of LocalDate and LocalTime with the contatenated format as shown in the figure above.

private static void testLocalDateTime() {LocalDate localDate = LocalDate.now();LocalTime time = LocalTime.now();LocalDateTime localDateTime = LocalDateTime.of(localDate, time);System.out.println(localDateTime.toString());LocalDateTime now = LocalDateTime.now();System.out.println(now);}

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Instant

private static void testInstant() throws InterruptedException {Instant start = Instant.now();Thread.sleep(1000L);Instant end = Instant.now();Duration duration = Duration.between(start, end);System.out.println(duration.toMillis());}

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Period

private static void testPeriod() {Period period = Period.between(LocalDate.of(2020, 5, 10),LocalDate.of(2021, 3, 4));System.out.println(period.getYears());System.out.println(period.getMonths());System.out.println(period.getDays());}

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Duration

private static void testDuration() {LocalTime time = LocalTime.now();System.out.println(time);LocalTime beforeTime = time.minusHours(2);System.out.println(beforeTime);Duration duration = Duration.between(beforeTime,time );System.out.println(duration.toHours());}

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format

private static void testDateFormat() {LocalDate localDate = LocalDate.now();String format1 = localDate.format(DateTimeFormatter.BASIC_ISO_DATE);System.out.println(format1);DateTimeFormatter mySelfFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");String format = localDate.format(mySelfFormatter);System.out.println(format);}

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parse

private static void testDateParse() {String date1 = "20210305";LocalDate localDate = LocalDate.parse(date1, DateTimeFormatter.BASIC_ISO_DATE);System.out.println(localDate);DateTimeFormatter mySelfFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");String date2 = "2021-03-05";LocalDate localDate2 = LocalDate.parse(date2, mySelfFormatter);System.out.println(localDate2);}

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總結

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