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; } }