JAVA8-Date and Time API： LocalDate, LocalTime, Instant, Duration, Period JAVA8-Date and Time API： LocalDate, LocalTime, Instant, Duration, Period旧API问题1、代码不清晰，一下看不出要转换的日期。2、Date日期中还包含了时间 3、多线程情况下会报错。代码重现：package com.example.study.java8.datetime; import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date; public class DateTest { public static void main(String[] args) throws ParseException { //122格林威治时间 11月 23日期 //问题：不能清晰表示日期 Date date = new Date(122, 11, 23); System.out.println(date); //多线程情况下会出现一些问题： //30个线程，每个线程下循环100次，执行时间格式转换。 SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd"); for (int i = 0; i < 30; i++) { new Thread(() -> { for (int j = 0; j < 100; j++) { Date parseDate = null; try { parseDate = sdf.parse("20221123"); } catch (ParseException e) { e.printStackTrace(); } System.out.println(parseDate); } }).start(); } } }输出结果：Fri Dec 23 00:00:00 CST 2022 .。。。。。。。。。。 java.lang.NumberFormatException: For input string: "" at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.base/java.lang.Long.parseLong(Long.java:702) at java.base/java.lang.Long.parseLong(Long.java:817) at java.base/java.text.DigitList.getLong(DigitList.java:195) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2121) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1931) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.example.study.java8.datetime.DateTest.lambda$main$0(DateTest.java:22) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "Thread-25" Exception in thread "Thread-14" java.lang.NumberFormatException: multiple points at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1914) at java.base/jdk.internal.math.FloatingDecimal.parseDouble(FloatingDecimal.java:110)新API学习1、LocalDate 线程安全package com.example.study.java8.datetime; import java.text.ParseException; import java.text.SimpleDateFormat; import java.time.LocalDate; import java.time.temporal.ChronoField; import java.util.Date; /** * java8 Date and Time API：LocalDate 线程安全 */ public class DateTestApi { public static void main(String[] args) { testLocalDate(); } private static void testLocalDate() { //1、LocalDate LocalDate localDate = LocalDate.of(2022, 11, 23); System.out.println(localDate); //获取年 System.out.println(localDate.getYear()); //获取月 System.out.println(localDate.getMonth()); //今年的第几天 System.out.println(localDate.getDayOfYear()); //这个月的第几天 System.out.println(localDate.getDayOfMonth()); //这一周的星期几 System.out.println(localDate.getDayOfWeek()); //整数：这个月的第几天 //其它枚举值用法一样 int dayOfMoth = localDate.get(ChronoField.DAY_OF_MONTH); System.out.println(dayOfMoth); //获取当前时间 LocalDate nowLocalDate = LocalDate.now(); System.out.println(nowLocalDate); } }输出结果：2022-11-23 2022 NOVEMBER 327 23 WEDNESDAY 23 2022-11-232、LocalTimepackage com.example.study.java8.datetime; import java.text.ParseException; import java.text.SimpleDateFormat; import java.time.LocalDate; import java.time.LocalTime; import java.time.temporal.ChronoField; import java.util.Date; /** * java8 Date and Time API：LocalDate 线程安全 */ public class DateTestApi { public static void main(String[] args) { testLocalTime(); } private static void testLocalTime(){ //获取当前时间 LocalTime time = LocalTime.now(); System.out.println(time); //时 System.out.println(time.getHour()); //分 System.out.println(time.getMinute()); //秒 System.out.println(time.getSecond()); } }输出结果：21:19:22.856586500 21 19 223、LocalDateTime，提供的api更丰富，线程更安全package com.example.study.java8.datetime; import java.text.ParseException; import java.text.SimpleDateFormat; import java.time.LocalDate; import java.time.LocalDateTime; import java.time.LocalTime; import java.time.temporal.ChronoField; import java.util.Date; /** * java8 Date and Time API：LocalDate 线程安全 */ public class DateTestApi { public static void main(String[] args) { combineLocalDateAndTime(); } // API-2: LocalDateTime 日期时间 private static void combineLocalDateAndTime() { // 整合LocalDate和LocalTIme LocalDate date = LocalDate.now(); LocalTime time = LocalTime.now(); LocalDateTime dateTime = LocalDateTime.of(date, time); System.out.println(dateTime); //直接获取当前日期时间 LocalDateTime now = LocalDateTime.now(); System.out.println(now); //获取日期时间，是一周中的周几，其它api方法用法一样 System.out.println(now.getDayOfWeek()); } }输出结果：2022-11-23T21:28:37.228619600 2022-11-23T21:28:37.229621100 WEDNESDAY4、Instant 点，时刻，时间点package com.example.study.java8.datetime; import java.text.ParseException; import java.text.SimpleDateFormat; import java.time.*; import java.time.temporal.ChronoField; import java.util.Date; /** * java8 Date and Time API：LocalDate 线程安全 */ public class DateTestApi { public static void main(String[] args) throws InterruptedException { testInstant(); } //API-4 Instant 时间点，时刻，点 private static void testInstant() throws InterruptedException { Instant start = Instant.now(); Thread.sleep(1000L); Instant end = Instant.now(); //Duration 时间段 Duration duration = Duration.between(start, end); System.out.println(duration.toMillis()); } }输出结果：10095、Duration 时间段package com.example.study.java8.datetime; import java.text.ParseException; import java.text.SimpleDateFormat; import java.time.*; import java.time.temporal.ChronoField; import java.util.Date; /** * java8 Date and Time API：LocalDate 线程安全 */ public class DateTestApi { public static void main(String[] args) throws InterruptedException { testDuration(); } //API-5 Duration 时间段 private static void testDuration() { LocalTime start = LocalTime.now(); //减1小时 LocalTime end = start.minusHours(1); //开始到结束 Duration durationBetween = Duration.between(end, start); //用了多少小时 System.out.println(durationBetween.toHours()); } } 输出结果：16、Period 周期、时期、时代package com.example.study.java8.datetime; import java.text.ParseException; import java.text.SimpleDateFormat; import java.time.*; import java.time.temporal.ChronoField; import java.util.Date; /** * java8 Date and Time API：LocalDate 线程安全 */ public class DateTestApi { public static void main(String[] args) throws InterruptedException { testPeriod(); } //API-6 Period private static void testPeriod() { Period period = Period.between(LocalDate.of(2000, 10, 9), LocalDate.of(2022, 12, 13)); System.out.println(period.getYears()); System.out.println(period.getMonths()); System.out.println(period.getDays()); } } 输出结果：22 2 47、format 日期时间格式化成字符串package com.example.study.java8.datetime; import java.text.Format; 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; /** * java8 Date and Time API：LocalDate 线程安全 */ public class DateTestApi { public static void main(String[] args) throws InterruptedException { testLocalDateFormat(); } //API-7 format 日期时间格式化成字符串 private static void testLocalDateFormat() { //日期格式化 LocalDate date = LocalDate.now(); String basicDate = date.format(DateTimeFormatter.BASIC_ISO_DATE); //日期时间格式化 LocalDateTime now = LocalDateTime.now(); String time = now.format(DateTimeFormatter.ISO_LOCAL_TIME); System.out.println(basicDate); System.out.println(time); //自定义格式化格式 LocalDateTime localDateTime = LocalDateTime.now(); //自定义格式 DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"); String formatDateTIme = localDateTime.format(formatter); System.out.println(formatDateTIme); } } 输出结果：20221124 20:28:09.71863167、parse 字符串格式化成日期时间package com.example.study.java8.datetime; import java.text.Format; 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; /** * java8 Date and Time API：LocalDate 线程安全 */ public class DateTestApi { public static void main(String[] args) throws InterruptedException { testLocalDateParse(); } //API-7 parse 字符串转日期时间格式 private static void testLocalDateParse() { //字符串日期转date类型，注意字符串格式和要转换的格式要一样 String date = "2022-11-24"; DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd"); LocalDate localDate = LocalDate.parse(date, formatter); System.out.println(localDate); //字符串时间转time类型，注意字符串格式和要转换的格式要一样 String time = "20:38:24"; DateTimeFormatter timeFormatter = DateTimeFormatter.ofPattern("HH:mm:ss"); LocalTime localTime = LocalTime.parse(time, timeFormatter); System.out.println(localTime); //字符串日期时间转datetime类型，注意字符串格式和要转换的格式要一样 String dateTime = "2022/11/24 20:59:24"; DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss"); LocalDateTime localDateTime = LocalDateTime.parse(dateTime, dateTimeFormatter); System.out.println(localDateTime); } } 输出结果：2022-11-24 20:38:24 2022-11-24T20:59:24java.time：更多API可以根据需要查看该包下的时间工具类。

AVA8-CompletableFuture常用API：runAfterBoth、applyToEither、acceptEither 、runAfterEither 、allOf、anyOf AVA8-CompletableFuture常用API：runAfterBoth、applyToEither、acceptEither 、runAfterEither 、allOf、anyOf1、runAfterBoth ：2个CompletableFuture都执行完后,再执行其它操作package com.example.study.java8.completableFutures.api; import java.util.concurrent.CompletableFuture; public class CompletableFutureAction2 { public static void main(String[] args) throws InterruptedException { //API-- 1、runAfterBoth: 2个都执行完后,再执行其它操作 CompletableFuture.supplyAsync(() -> { System.out.println(Thread.currentThread().getName() + "this is runing 1......"); return 1; }) .runAfterBoth(CompletableFuture.supplyAsync(() -> { System.out.println(Thread.currentThread().getName() + "this is runing 2......"); return 2; }), () -> System.out.println("done")); //为了防止主线程结束后，守护线程被关闭，模拟修改10000毫秒 Thread.sleep(10000); } }输出结果：ForkJoinPool.commonPool-worker-5this is runing 2...... ForkJoinPool.commonPool-worker-19this is runing 1...... done2、 applyToEither：其中一个CompletableFuture执行完，就将结果传给另一个Fuctionpackage com.example.study.java8.completableFutures.api; import java.util.concurrent.CompletableFuture; public class CompletableFutureAction2 { public static void main(String[] args) throws InterruptedException { //API-- 2、runAfterBoth: 其中一个CompletableFuture执行完，就将结果传递到另一个Function中。 CompletableFuture.supplyAsync(()->{ try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName()+"this is one future..."); return 1; }).applyToEither(CompletableFuture.supplyAsync(()->{ try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName()+"this is two future..."); return 2; }), v-> 10 * v ).thenAccept(System.out::println); //为了防止主线程结束后，守护线程被关闭，模拟修改10000毫秒 Thread.sleep(10000); } }输出结果：ForkJoinPool.commonPool-worker-5this is two future... 20 ForkJoinPool.commonPool-worker-19this is one future...3、acceptEither ：其中一个future执行完，就将结果传递到cutomer中消费package com.example.study.java8.completableFutures.api; import java.util.concurrent.CompletableFuture; public class CompletableFutureAction2 { public static void main(String[] args) throws InterruptedException { //API-- 3、acceptEither: 其中一个CompletableFuture执行完，就将结果传递到另一个Function中。 CompletableFuture.supplyAsync(()->{ try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName()+"this is one future..."); return 1; }).acceptEither(CompletableFuture.supplyAsync(()->{ try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName()+"this is two future..."); return 2; }), System.out::println ); //为了防止主线程结束后，守护线程被关闭，模拟修改10000毫秒 Thread.sleep(10000); } }输出结果：ForkJoinPool.commonPool-worker-5this is two future... 2 ForkJoinPool.commonPool-worker-19this is one future...4、runAfterEither :其中一个CompletableFuture执行完，就可以做其它操作了。不会将结果传递，可以做类似其中一个操作完后的消息通知功能。package com.example.study.java8.completableFutures.api; import java.util.concurrent.CompletableFuture; public class CompletableFutureAction2 { public static void main(String[] args) throws InterruptedException { //API-- 4、runAfterEither: 其中一个CompletableFuture执行完，就可以做其它操作了。不会将结果传递，可以做类似其中一个操作完后的消息通知功能。 CompletableFuture.supplyAsync(()->{ try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName()+"this is one future..."); return 1; }).runAfterEither(CompletableFuture.supplyAsync(()->{ try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName()+"this is two future..."); return 2; }),()-> System.out.println("其中一个future执行完成") ); //为了防止主线程结束后，守护线程被关闭，模拟修改10000毫秒 Thread.sleep(10000); } }输出结果：ForkJoinPool.commonPool-worker-5this is two future... 其中一个future执行完成 ForkJoinPool.commonPool-worker-19this is one future...5、 allOf： 静态方法，可直接调用。全部future执行完后，再进行消费package com.example.study.java8.completableFutures.api; import java.util.Arrays; import java.util.List; import java.util.concurrent.CompletableFuture; import static java.util.stream.Collectors.toList; public class CompletableFutureAction2 { public static void main(String[] args) throws InterruptedException { //API-- 5、allOf: 静态方法，可直接调用。全部future执行完后，再进行消费 List<CompletableFuture<Double>> completableFutureList = Arrays.asList(1, 2, 3, 4, 5) .stream().map(i -> CompletableFuture.supplyAsync((CompletableFutureAction2::get))) .collect(toList()); CompletableFuture[] completableFuturesArray = completableFutureList.toArray(new CompletableFuture[completableFutureList.size()]); CompletableFuture.allOf(completableFuturesArray).thenRun(()-> System.out.println("所有future执行完成")); //为了防止主线程结束后，守护线程被关闭，模拟修改10000毫秒 Thread.sleep(50000); } }输出结果：0.5653558041825968 0.5720868499613329 0.25643461386243427 0.9522248509043018 0.5483123698045103 所有future执行完成6、anyOf ：静态方法，可直接调用。其中一个future执行完后，就进行消费package com.example.study.java8.completableFutures.api; import java.util.Arrays; import java.util.Collection; import java.util.List; import java.util.Random; import java.util.concurrent.CompletableFuture; import static java.util.stream.Collectors.toList; public class CompletableFutureAction2 { private final static Random RANDOM = new Random(System.currentTimeMillis()); public static void main(String[] args) throws InterruptedException { //API-- 6、anyOf: 静态方法，可直接调用。其中一个future执行完后，就进行消费 List<CompletableFuture<Double>> futureList = Arrays.asList(1, 2, 3, 4, 5) .stream() .map(i -> CompletableFuture.supplyAsync(CompletableFutureAction2::get)) .collect(toList()); CompletableFuture[] futuresArray = futureList.toArray(new CompletableFuture[futureList.size()]); CompletableFuture.anyOf(futuresArray).thenRun(()-> System.out.println("其中一个future已执行完成")); //为了防止主线程结束后，守护线程被关闭，模拟修改10000毫秒 Thread.sleep(50000); } static double get(){ try { Thread.sleep(RANDOM.nextInt(100)); } catch (InterruptedException e) { e.printStackTrace(); } double value = RANDOM.nextDouble(); System.out.println(value); return value; } } 输出结果：0.41392777550489923 其中一个future已执行完成 0.7321854786542472 0.015636586751138104 0.8968276147964326 0.26576407363892185AVA8-CompletableFuture常用API：1、runAfterBoth2、applyToEither 3、acceptEither 4 、runAfterEither 5 、allOf 6、anyOf

JAVA8-CompletableFuture常用API：thenApply、handle、thenRun、thenAccept、thenCompose、thenCombine、thenAcceptBoth JAVA8-CompletableFuture常用API：thenApply、handle、thenRun、thenAccept、thenCompose、thenCombine、thenAcceptBoth1、thenApplypackage com.example.study.java8.completableFutures.api; import java.util.Optional; import java.util.concurrent.CompletableFuture; /** * CompletableFuture常用API: thenApply、handle */ public class CompletableFutureAtion1 { public static void main(String[] args) throws InterruptedException { //API-- 1、thenApply //模拟其它 异步 逻辑操作然后返回结果1 CompletableFuture.supplyAsync(() -> 1) .thenApply(i -> Integer.sum(i, 10)) //thenApply 将结果加10 .whenComplete((v, t) -> Optional.ofNullable(v).ifPresent(System.out::println)); //同步执行打印结果 // .whenCompleteAsync() //异步操作，可以将结果在进行其它逻辑异步操作 //whenComplete VS whenCompleteAsync //为了防止主线程结束后，守护线程被关闭，模拟修改10000毫秒 Thread.sleep(10000); } } 输出结果：11对比whenComplete VS whenCompleteAsync：whenCompleteAsync异步操作，可以将结果在进行其它逻辑异步操作。2、handlepackage com.example.study.java8.completableFutures.api; import java.util.Optional; import java.util.concurrent.CompletableFuture; /** * CompletableFuture常用API: thenApply、handle */ public class CompletableFutureAtion1 { public static void main(String[] args) throws InterruptedException { //API- 2、handle CompletableFuture.supplyAsync(() -> 1) .handle((v, t) -> Integer.sum(v, 10)) .whenComplete((v, t) -> Optional.ofNullable(v).ifPresent(System.out::println)); // thenApply VS handle :handle只是多了一个对堆内存的考虑。 //为了防止主线程结束后，守护线程被关闭，模拟修改10000毫秒 Thread.sleep(10000); } } 输出结果：11对比thenApply VS handle :handle只是多了一个对堆内存的考虑。3、thenRunpackage com.example.study.java8.completableFutures.api; import java.util.Optional; import java.util.concurrent.CompletableFuture; /** * CompletableFuture常用API: thenApply、handle */ public class CompletableFutureAtion1 { public static void main(String[] args) throws InterruptedException { //API-3、thenRun:所有结果执行完后，执行其它操作 CompletableFuture.supplyAsync(() -> 1) .handle((v, t) -> Integer.sum(v, 10)) .whenComplete((v, t) -> Optional.ofNullable(v).ifPresent(System.out::println)) .thenRun(System.out::println); //这里没有入参，只会打印一个换行 // .thenRunAsync() 如果做成异步的就用这个方法 //为了防止主线程结束后，守护线程被关闭，模拟修改10000毫秒 Thread.sleep(10000); } }输出结果：11 //这里打印了一个换行对比thenRun VS thenRunAsync ：thenRunAsync 做成异步的就用这个方法。4、thenAcceptpackage com.example.study.java8.completableFutures.api; import java.util.Optional; import java.util.concurrent.CompletableFuture; /** * CompletableFuture常用API: thenApply、handle */ public class CompletableFutureAtion1 { public static void main(String[] args) throws InterruptedException { //API-4、thenAccept:不会有任何返回值,只是对结果进行消费 CompletableFuture.supplyAsync(() -> 1) .thenAccept(System.out::println); //为了防止主线程结束后，守护线程被关闭，模拟修改10000毫秒 Thread.sleep(10000); } } 输出结果：15、thenComposepackage com.example.study.java8.completableFutures.api; import java.util.Optional; import java.util.concurrent.CompletableFuture; /** * CompletableFuture常用API: thenApply、handle */ public class CompletableFutureAtion1 { public static void main(String[] args) throws InterruptedException { //API-5、thenCompose:将异步产生的结果，再交(组合)给另一个ComletableFuture进行处理，是有返回值的。 CompletableFuture.supplyAsync(() -> 1) .thenCompose(i -> CompletableFuture.supplyAsync(() -> 10 * i)) //将1再组合成另一个CompletableFuture处理 .thenAccept(System.out::println); //然后消费，直接输出结果 //为了防止主线程结束后，守护线程被关闭，模拟修改10000毫秒 Thread.sleep(10000); } }输出结果：106、thenCombinepackage com.example.study.java8.completableFutures.api; import java.util.Optional; import java.util.concurrent.CompletableFuture; /** * CompletableFuture常用API: thenApply、handle */ public class CompletableFutureAtion1 { public static void main(String[] args) throws InterruptedException { //API-6、thenCombine:将异步产生的结果，与另一个CompletableFuture结果，作为参数进行处理,有返回值。 CompletableFuture.supplyAsync(() -> 1) .thenCombine(CompletableFuture.supplyAsync(()->0.2),(v1,v2)->v1+v2) .thenAccept(System.out::println); //为了防止主线程结束后，守护线程被关闭，模拟修改10000毫秒 Thread.sleep(10000); } }输出结果：1.27、thenAcceptBothpackage com.example.study.java8.completableFutures.api; import java.util.Optional; import java.util.concurrent.CompletableFuture; /** * CompletableFuture常用API: thenApply、handle */ public class CompletableFutureAtion1 { public static void main(String[] args) throws InterruptedException { //API-7、thenAcceptBoth:将异步产生的结果，与另一个CompletableFuture结果，作为参数进行处理，没有返回值，直接用于消费。 CompletableFuture.supplyAsync(() -> 1) .thenAcceptBoth(CompletableFuture.supplyAsync(()->0.5), (v1,v2)->{ System.out.println(v1); System.out.println(v2); }); // thenCombine VS thenAcceptBoth：2个方法类似，有个有返回值，有个没有返回值。 //为了防止主线程结束后，守护线程被关闭，模拟修改10000毫秒 Thread.sleep(10000); } } 输出结果：1 0.5CompletableFuture常用API使用：1、thenApply2、handle3、thenRun4、thenAccept5、thenCompose6、thenCombine7、thenAcceptBoth

JAVA8-CompletableFuture流水线工作，join多个异步任务详解 JAVA8-CompletableFuture流水线工作，join多个异步任务详解需求：根据商品id，将每个商品价格翻2倍？代码示例package com.example.study.java8.completableFutures; import java.util.Arrays; import java.util.List; import java.util.Random; import java.util.concurrent.CompletableFuture; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.stream.Stream; import static java.util.stream.Collectors.toList; /** * 根据商品id，将每个商品价格翻2倍。CompletableFuture高并发执行。 */ public class CompletableFutureInAction4 { private final static Random RANDOM = new Random(System.currentTimeMillis()); public static void main(String[] args) { //防止主线程执行完后，守护线程也关闭 ExecutorService executorService = Executors.newFixedThreadPool(2, r -> { Thread thread = new Thread(r); thread.setDaemon(false); return thread; }); //5个商品ID List<Integer> productIDs = Arrays.asList(1, 2, 3, 4, 5); //通过CompletableFuture查询5个商品价格 Stream<CompletableFuture<Double>> completableFutureStream = productIDs.stream().map(i -> CompletableFuture.supplyAsync(() -> queryProduct(i), executorService)); //将每个商品价格翻2倍 Stream<CompletableFuture<Double>> multplyFutures = completableFutureStream.map(future -> future.thenApply(CompletableFutureInAction4::multply)); //将翻倍后的CompletableFuture加入线程中，将翻倍后价格收集成一个list数组 List<Double> result = multplyFutures.map(CompletableFuture::join).collect(toList()); //输出最后翻倍价格 System.out.println(result); } private static Double multply(Double value) { try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } return value * 2D; } private static Double queryProduct(int i){ return CompletableFutureInAction4.get(); } //模拟从数据库根据商品ID查询价格 static double get(){ try { Thread.sleep(RANDOM.nextInt(100)); } catch (InterruptedException e) { e.printStackTrace(); } double value = RANDOM.nextDouble(); System.out.println(value); return value; } }输出结果：0.22471854337617791 0.11072895680534822 0.6087836739979867 0.3209858426806811 0.8416829454071859 [0.44943708675235583, 0.22145791361069644, 1.2175673479959734, 0.6419716853613622, 1.6833658908143718]原理图 说明：Sequential(串行操作)：将第一个商品价格查询，然后翻倍，获取翻倍后价格，然后查询第二个商品，在将第二个商品价格翻倍，。。。一次执行完后，将所有的返回价格放到结果中。Parrallel（并行操作）：5个商品同时执行价格查询，价格翻倍任务，同时将返回价格放到结果中。明显看出Parrallel并行操作会快很多。缩减后代码package com.example.study.java8.completableFutures; import java.util.Arrays; import java.util.List; import java.util.Random; import java.util.concurrent.CompletableFuture; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.stream.Stream; import static java.util.stream.Collectors.toList; /** * 根据商品id，将每个商品价格翻2倍。利用CompletableFuture的高并发执行。代码缩减后更简洁。 */ public class CompletableFutureInAction5 { private final static Random RANDOM = new Random(System.currentTimeMillis()); public static void main(String[] args) { //防止主线程执行完后，守护线程也关闭 ExecutorService executorService = Executors.newFixedThreadPool(2, r -> { Thread thread = new Thread(r); thread.setDaemon(false); return thread; }); //5个商品ID List<Integer> productIDs = Arrays.asList(1, 2, 3, 4, 5); //通过CompletableFuture查询5个商品价格,并将价格翻2倍 List<Double> result = productIDs .stream() .map(i -> CompletableFuture.supplyAsync(() -> queryProduct(i), executorService)) .map(future -> future.thenApply(CompletableFutureInAction5::multply)) .map(CompletableFuture::join).collect(toList()); //输出最后翻倍价格 System.out.println(result); } private static Double multply(Double value) { try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } return value * 2D; } private static Double queryProduct(int i) { return CompletableFutureInAction5.get(); } //模拟从数据库根据商品ID查询价格 static double get() { try { Thread.sleep(RANDOM.nextInt(100)); } catch (InterruptedException e) { e.printStackTrace(); } double value = RANDOM.nextDouble(); System.out.println(value); return value; } }

JAVA8-CompletableFuture基本用法 JAVA8-CompletableFuture基本用法针对<实现一个异步基于事件回调的Future程序> 用CompletableFuture进行改进。代码示例：package com.example.study.java8.completableFutures; import java.util.Optional; import java.util.Random; import java.util.concurrent.CompletableFuture; import java.util.concurrent.ExecutionException; /** * CompletableFuture 基本用法 */ public class CompletableFutureInAction1 { private final static Random RANDOM = new Random(System.currentTimeMillis()); public static void main(String[] args) throws ExecutionException, InterruptedException { //实际开发中，一般不直接new，而是使用工厂创建 // CompletableFuture<Void> voidCompletableFuture = CompletableFuture.runAsync(); CompletableFuture<Double> completableFuture = new CompletableFuture<>(); new Thread(()->{ double value = get(); completableFuture.complete(value); }).start(); //不会阻塞程序执行 System.out.println("===========no====block====.."); //1、后面获取程序执行结果 // Optional.ofNullable(completableFuture.get()).ifPresent(System.out::println); //2、执行完后，通过回调自动返回结果 completableFuture.whenComplete((v,t)->{ Optional.ofNullable(v).ifPresent(System.out::println); Optional.ofNullable(t).ifPresent(x->x.printStackTrace()); }); } private static double get(){ try { Thread.sleep(RANDOM.nextInt(10000)); } catch (InterruptedException e) { e.printStackTrace(); } return RANDOM.nextDouble(); } }输出结果：===========no====block====.. 0.5192854493861505