Java 8 新增的时间API

Posted 2021-05-16 认真对待世界的小白

一、旧 API 存在多线程安全问题

import java.text.SimpleDateFormat;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class TestSimpleDateFormat {

    public static void main(String[] args) throws Exception {
        
        /*SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
        
        Callable<Date> task = new Callable<Date>() {

            @Override
            public Date call() throws Exception {
                return sdf.parse("20161121");
            }
            
        };

        ExecutorService pool = Executors.newFixedThreadPool(10);
        
        List<Future<Date>> results = new ArrayList<>();
        
        for (int i = 0; i < 10; i++) {
            results.add(pool.submit(task));
        }
        
        for (Future<Date> future : results) {
            System.out.println(future.get());
        }
        
        pool.shutdown();*/

        //解决多线程安全问题
        /*Callable<Date> task = new Callable<Date>() {

            @Override
            public Date call() throws Exception {
                return DateFormatThreadLocal.convert("20161121");
            }
            
        };

        ExecutorService pool = Executors.newFixedThreadPool(10);
        
        List<Future<Date>> results = new ArrayList<>();
        
        for (int i = 0; i < 10; i++) {
            results.add(pool.submit(task));
        }
        
        for (Future<Date> future : results) {
            System.out.println(future.get());
        }
        
        pool.shutdown();*/

        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyyMMdd");

        Callable<LocalDate> task = new Callable<LocalDate>() {

            @Override
            public LocalDate call() throws Exception {
                LocalDate ld = LocalDate.parse("20161121", dtf);
                return ld;
            }

        };

        ExecutorService pool = Executors.newFixedThreadPool(10);

        List<Future<LocalDate>> results = new ArrayList<>();

        for (int i = 0; i < 10; i++) {
            results.add(pool.submit(task));
        }

        for (Future<LocalDate> future : results) {
            System.out.println(future.get());
        }

        pool.shutdown();
    }
}

旧 API 解决线程安全问题的方式——加锁

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class DateFormatThreadLocal {
    private static final ThreadLocal<DateFormat> df = new ThreadLocal<DateFormat>() {

        protected DateFormat initialValue() {
            return new SimpleDateFormat("yyyyMMdd");
        }

    };

    public static final Date convert(String source) throws ParseException {
        return df.get().parse(source);
    }
}

二、新 API 应用

import java.time.DayOfWeek;
import java.time.Duration;
import java.time.Instant;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.OffsetDateTime;
import java.time.Period;
import java.time.ZoneId;
import java.time.ZoneOffset;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;
import java.time.temporal.TemporalAdjusters;
import java.util.Set;

import org.junit.Test;

public class TestLocalDateTime {

    //6.ZonedDate、ZonedTime、ZonedDateTime ： 带时区的时间或日期
    @Test
    public void test7() {
        LocalDateTime ldt = LocalDateTime.now(ZoneId.of("Asia/Shanghai"));
        System.out.println(ldt);

        ZonedDateTime zdt = ZonedDateTime.now(ZoneId.of("US/Pacific"));
        System.out.println(zdt);
    }

    @Test
    public void test6() {
        Set<String> set = ZoneId.getAvailableZoneIds();
        set.forEach(System.out::println);
    }


    //5. DateTimeFormatter : 解析和格式化日期或时间
    @Test
    public void test5() {
//        DateTimeFormatter dtf = DateTimeFormatter.ISO_LOCAL_DATE;

        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy年MM月dd日 HH:mm:ss E");

        LocalDateTime ldt = LocalDateTime.now();
        String strDate = ldt.format(dtf);

        System.out.println(strDate);

        LocalDateTime newLdt = ldt.parse(strDate, dtf);
        System.out.println(newLdt);
    }

    //4. TemporalAdjuster : 时间校正器
    @Test
    public void test4() {
        LocalDateTime ldt = LocalDateTime.now();
        System.out.println(ldt);

        LocalDateTime ldt2 = ldt.withDayOfMonth(10);
        System.out.println(ldt2);

        LocalDateTime ldt3 = ldt.with(TemporalAdjusters.next(DayOfWeek.SUNDAY));
        System.out.println(ldt3);

        //自定义：下一个工作日
        LocalDateTime ldt5 = ldt.with((l) -> {
            LocalDateTime ldt4 = (LocalDateTime) l;

            DayOfWeek dow = ldt4.getDayOfWeek();

            if (dow.equals(DayOfWeek.FRIDAY)) {
                return ldt4.plusDays(3);
            } else if (dow.equals(DayOfWeek.SATURDAY)) {
                return ldt4.plusDays(2);
            } else {
                return ldt4.plusDays(1);
            }
        });

        System.out.println(ldt5);

    }

    //3.
    //Duration : 用于计算两个“时间”间隔
    //Period : 用于计算两个“日期”间隔
    @Test
    public void test3() {
        Instant ins1 = Instant.now();

        System.out.println("--------------------");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
        }

        Instant ins2 = Instant.now();

        System.out.println("所耗费时间为：" + Duration.between(ins1, ins2));

        System.out.println("----------------------------------");

        LocalDate ld1 = LocalDate.now();
        LocalDate ld2 = LocalDate.of(2011, 1, 1);

        Period pe = Period.between(ld2, ld1);
        System.out.println(pe.getYears());
        System.out.println(pe.getMonths());
        System.out.println(pe.getDays());
    }

    //2. Instant : 时间戳。 （使用 Unix 元年  1970年1月1日 00:00:00 所经历的毫秒值）
    @Test
    public void test2() {
        Instant ins = Instant.now();  //默认使用 UTC 时区
        System.out.println(ins);

        OffsetDateTime odt = ins.atOffset(ZoneOffset.ofHours(8));
        System.out.println(odt);

        System.out.println(ins.getNano());

        Instant ins2 = Instant.ofEpochSecond(5);
        System.out.println(ins2);
    }

    //1. LocalDate、LocalTime、LocalDateTime
    @Test
    public void test1() {
        LocalDateTime ldt = LocalDateTime.now();
        System.out.println(ldt);

        LocalDateTime ld2 = LocalDateTime.of(2016, 11, 21, 10, 10, 10);
        System.out.println(ld2);

        LocalDateTime ldt3 = ld2.plusYears(20);
        System.out.println(ldt3);

        LocalDateTime ldt4 = ld2.minusMonths(2);
        System.out.println(ldt4);

        System.out.println(ldt.getYear());
        System.out.println(ldt.getMonthValue());
        System.out.println(ldt.getDayOfMonth());
        System.out.println(ldt.getHour());
        System.out.println(ldt.getMinute());
        System.out.println(ldt.getSecond());
    }
}