深入理解Java8新特性之新日期时间API的应用

1.新旧对比（线程安全问题）

我们先来看下面的代码：???????????? （关于代码中某些类中的某些方法，我在这里就不说了，大家可以去查找api文档）

package com.szh.java8.datetime;
 
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.*;
 
/**
 *
 */
public class testsimpledateformat {
 
    public static void main(string[] args) throws executionexception, interruptedexception {
        simpledateformat sdf = new simpledateformat("yyyymmdd");
 
        callable<date> task1 = new callable<date>() {
            @override
            public date call() throws exception {
                return sdf.parse("20211109");
            }
        };
 
        executorservice pool1 = executors.newfixedthreadpool(10);
        list<future<date>> futurelist1 = new arraylist<>();
        for (int i = 0; i < 10; i++) {
            futurelist1.add(pool1.submit(task1));
        }
 
        for (future<date> future : futurelist1) {
            system.out.println(future.get());
        }
 
        pool1.shutdown();
 
        //=================================================================
 
//        datetimeformatter dtf = datetimeformatter.ofpattern("yyyymmdd");
//
//        callable<localdate> task2 = new callable<localdate>() {
//            @override
//            public localdate call() throws exception {
//                return localdate.parse("20211109",dtf);
//            }
//        };
//
//        executorservice pool2 = executors.newfixedthreadpool(10);
//        list<future<localdate>> futurelist2 = new arraylist<>();
//        for (int i = 0; i < 10; i++) {
//            futurelist2.add(pool2.submit(task2));
//        }
//
//        for (future<localdate> future : futurelist2) {
//            system.out.println(future.get());
//        }
//
//        pool2.shutdown();
    }
}

运行之后，就出现了线程安全问题。

将代码中的上半部分注释掉，然后打开下半部分的代码，再次运行，线程安全问题就不存在了。

也就是java8中提供了新一套日期时间api已经解决了线程安全问题。

2.localdate

package com.szh.java8.datetime;
 
import java.time.localdate;
 
/**
 *
 */
public class testlocaldate {
 
    public static void main(string[] args) {
        localdate ld1 = localdate.now();
        system.out.println(ld1);
 
        localdate ld2 = localdate.of(2021,5,1);
        system.out.println(ld2);
 
        localdate ld3 = ld1.plusyears(20);
        system.out.println(ld3);
 
        localdate ld4 = ld1.minusmonths(3);
        system.out.println(ld4);
 
        system.out.println(ld1.isbefore(ld2));
        system.out.println(ld2.isafter(ld1));
        system.out.println(ld1.isleapyear());
 
        system.out.println("年：" + ld1.getyear() + ", 月：" + ld1.getmonth() + ", 日：" + ld1.getdayofmonth());
        system.out.println("年：" + ld1.getyear() + ", 月：" + ld1.getmonthvalue() + ", 日：" + ld1.getdayofmonth());
    }
}

3.localtime

package com.szh.java8.datetime;
 
import java.time.localtime;
 
/**
 *
 */
public class testlocaltime {
 
    public static void main(string[] args) {
        localtime lt1 = localtime.now();
        system.out.println(lt1);
 
        localtime lt2 = localtime.of(13,14,15);
        system.out.println(lt2);
 
        localtime lt3 = lt2.plushours(3);
        system.out.println(lt3);
 
        localtime lt4 = lt2.minusminutes(14);
        system.out.println(lt4);
 
        system.out.println(lt1.isbefore(lt2));
        system.out.println(lt2.isafter(lt1));
        system.out.println("小时：" + lt1.gethour() + ", 分钟：" + lt1.getminute() + ", 秒：" + lt1.getsecond());
    }
}

4.localdatetime

package com.szh.java8.datetime;
 
import java.time.localdatetime;
 
/**
 *
 */
public class testlocaldatetime {
 
    public static void main(string[] args) {
        localdatetime ldt1 = localdatetime.now();
        system.out.println(ldt1);
 
        localdatetime ldt2 = localdatetime.of(2020,5,1,13,14,15);
        system.out.println(ldt2);
 
        localdatetime ldt3 = ldt1.plusyears(15);
        system.out.println(ldt3);
 
        localdatetime ldt4 = ldt1.minusdays(20);
        system.out.println(ldt4);
 
        system.out.println(ldt1.isbefore(ldt2));
        system.out.println(ldt2.isafter(ldt1));
        system.out.println("年：" + ldt2.getyear() + ", 月：" + ldt2.getmonthvalue() + ", 日：" + ldt2.getdayofmonth()
                + ", 小时：" + ldt2.gethour() + ", 分钟：" + ldt2.getminute() + ", 秒：" + ldt2.getsecond());
    }
}

5.instant

package com.szh.java8.datetime;
 
import java.time.instant;
import java.time.offsetdatetime;
import java.time.zoneoffset;
 
/**
 * 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）
 *           默认使用 utc 时区
 */
public class testinstant {
 
    public static void main(string[] args) {
        instant instant1 = instant.now();
        system.out.println(instant1);
 
        offsetdatetime odt = instant1.atoffset(zoneoffset.ofhoursminutesseconds(8,16,32));
        system.out.println(odt);
 
        system.out.println(instant1.getepochsecond());
        system.out.println(instant1.toepochmilli());
 
        instant instant2 = instant.ofepochsecond(1000);
        system.out.println(instant2);
 
        instant instant3 = instant1.plusseconds(30);
        system.out.println(instant3);
 
        instant instant4 = instant1.minusseconds(50);
        system.out.println(instant4);
    }
}

6.duration、period

package com.szh.java8.datetime;
 
import java.time.duration;
import java.time.localdate;
import java.time.localtime;
import java.time.period;
 
/**
 * period : 用于计算两个“日期”间隔
 * duration : 用于计算两个“时间”间隔
 */
public class testperiodduration {
 
    public static void main(string[] args) {
        localdate ld1 = localdate.now();
        localdate ld2 = localdate.of(2020,5,1);
        period period = period.between(ld2,ld1);
        system.out.println("两个日期相差：" + period.getyears() + "年，" + period.getmonths() + "个月，"
                            + period.getdays() + "天....");
        system.out.println(period.isnegative()); //检查此期间的三个单位是否为负
        system.out.println(period.iszero()); //检查此期间的所有三个单位是否为零
 
        system.out.println("--------------------------------------------");
 
        localtime lt1 = localtime.now();
        try {
            thread.sleep(2000);
        } catch (interruptedexception e) {
            e.printstacktrace();
        }
        localtime lt2 = localtime.now();
        duration duration = duration.between(lt1,lt2);
        system.out.println("两个时间相差：" + duration.tohours() + "个小时，" + duration.tominutes() + "分钟，"
                            + duration.getseconds() + "秒....");
        system.out.println(duration.isnegative()); //检查此期间的三个单位是否为负
        system.out.println(duration.iszero()); //检查此期间的所有三个单位是否为零
    }
}

7.testtemporaladjuster、testtemporaladjusters

package com.szh.java8.datetime;
 
import java.time.dayofweek;
import java.time.localdatetime;
import java.time.temporal.temporaladjusters;
 
/**
 *  temporaladjuster : 时间校正器。有时我们可能需要获取例如：将日期调整到“下个周日”等操作。
 *  temporaladjusters : 该类通过静态方法提供了大量的常用 temporaladjuster 的实现。
 */
public class testtemporaladjuster {
 
    public static void main(string[] args) {
        localdatetime ldt1 = localdatetime.now();
        system.out.println(ldt1);
 
        localdatetime ldt2 = ldt1.withmonth(5);
        system.out.println(ldt2);
 
        localdatetime ldt3 = ldt1.with(temporaladjusters.next(dayofweek.saturday));
        system.out.println(ldt3);
 
        //自定义：下一个工作日
        localdatetime ldt4 = ldt1.with((l) -> {
            localdatetime ldt5 = (localdatetime) l;
            dayofweek dow = ldt5.getdayofweek();
 
            if (dow.equals(dayofweek.friday)) {
                return ldt5.plusdays(3);
            } else if (dow.equals(dayofweek.saturday)) {
                return ldt5.plusdays(2);
            } else {
                return ldt5.plusdays(1);
            }
        });
        system.out.println(ldt4);
    }
}

8.datetimeformatter

package com.szh.java8.datetime;
 
import java.time.localdatetime;
import java.time.format.datetimeformatter;
 
/**
 * 解析与格式化
 */
public class testdatetimeformatter {
 
    public static void main(string[] args) {
        datetimeformatter dtf1 = datetimeformatter.iso_local_date_time;
        localdatetime ldt1 = localdatetime.now();
 
        string strdate1 = ldt1.format(dtf1);
        system.out.println(strdate1);
 
        system.out.println("-----------------------------------");
 
        datetimeformatter dtf2 = datetimeformatter.ofpattern("yyyy年mm月dd日 hh:mm:ss");
        string strdate2 = ldt1.format(dtf2);
        system.out.println(strdate2);
 
        system.out.println("-----------------------------------");
 
        localdatetime newdate = ldt1.parse(strdate2, dtf2);
        system.out.println(newdate);
    }
}

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