Java8新特性 | 易学教程

1、CompletableFuture：

基本的方式创建CompletableFuture<T>对象

package future;

import java.util.Optional;
import java.util.Random;
import java.util.concurrent.CompletableFuture;

public class CompletableAction {

    private static Random random = new Random();

    public static void main(String[] args) {

        CompletableFuture<Double> completableFuture = new CompletableFuture<>();

        new Thread(() -> {
            Double i = get();
            completableFuture.complete(i);
        }).start();

        // 使用get方法，会进入阻塞，因此必须等到输出随机数，再输出 123123
        /*try {
            Optional.ofNullable(completableFuture.get()).ifPresent(System.out::println);
            System.out.println("123123");
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }*/

        // whenComplete() 方法不会进入阻塞，因此先输出 123123，再输出随机数
        completableFuture.whenComplete((v, t) -> {
            Optional.ofNullable(v).ifPresent(System.out::println);
            Optional.ofNullable(t).ifPresent(Throwable::printStackTrace);
        });
        System.out.println("123123");
    }

    public static Double get() {
        try {
            Thread.sleep(3000L);
            return (double) random.nextInt(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
            return null;
        }
    }
}

输出的结果：

通过CompletableFuture.supplyAsync(Supplier<T> supplier) 或者 CompletableFuture.supplyAsync(Supplier<T> supplier, Executor executor) 方法进行创建CompletableFuture对象实例

package future;

import java.util.Optional;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicBoolean;

public class CompletableAction2 {

    public static void main(String[] args) {

        AtomicBoolean atomicBoolean = new AtomicBoolean(false);

        ExecutorService executorService = Executors.newFixedThreadPool(2);
        ExecutorService executorService2 = Executors.newFixedThreadPool(2, (runnable) -> {
            Thread thread = new Thread(runnable);
            return thread;
        });

        // supplyAsync(Supplier<T> supplier, Executor executor) 方法，
        // 采用了 executorService.shutdown()方法 和 AtomicBoolean原子操作判断是否执行完，然后退出线程
        CompletableFuture.supplyAsync(CompletableAction::get, executorService2)
                .whenComplete((v, t) -> {
                    Optional.ofNullable(v).ifPresent(System.out::println);
                    Optional.ofNullable(t).ifPresent(Throwable::printStackTrace);
                    atomicBoolean.set(true);
                });
        System.out.println(123123);

        while (!atomicBoolean.get()) {
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        executorService2.shutdown();

        //================================================================

        // supplyAsync() 方法是一个守护线程，
        // 当main线程执行完，直接关闭线程，因此supplyAsync()方法的内容来不及打印输出
        /*CompletableFuture.supplyAsync(CompletableAction::get)
                .whenComplete((v, t) -> {
                    Optional.ofNullable(v).ifPresent(System.out::println);
                    Optional.ofNullable(t).ifPresent(Throwable::printStackTrace);
                });
        System.out.println(123123);*/

        // 让main线程运行停在这里，没与关闭
        /*try {
            Thread.currentThread().join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }*/
    }
}

CompletableFuture<T>的 thenApply() 方法和 join() 方法使用

package future;

import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.stream.Stream;

import static java.util.stream.Collectors.toList;

public class CompletableAction3 {

    public static void main(String[] args) {

        List<Integer> integers = Arrays.asList(1, 2, 3, 4, 5);

        AtomicBoolean atomicBoolean = new AtomicBoolean(false);
        ExecutorService executorService = Executors.newFixedThreadPool(2, (r) -> {
            Thread thread = new Thread(r);
            return thread;
        });

        /*CompletableFuture.supplyAsync(CompletableAction::get, executorService).whenComplete((v, t) -> {
            atomicBoolean.set(true);
            Optional.ofNullable(v).ifPresent(System.out::println);
            Optional.ofNullable(t).ifPresent(Throwable::printStackTrace);
        });

        while (!atomicBoolean.get()) {
            executorService.shutdown();
        }*/

        // 原始方式使用
        Stream<CompletableFuture<Double>> completableFutureStream = integers.stream().map(i -> {
            return CompletableFuture.supplyAsync(() -> CompletableAction3.getProductById(i), executorService);
        });

        Stream<Double> doubleStream = completableFutureStream.map(d -> {
            Double multiply = null;
            try {
                multiply = CompletableAction3.multiply(d.get());
            } catch (InterruptedException | ExecutionException e) {
                e.printStackTrace();
            }
            return multiply;
        });

        List<Double> doubleList = doubleStream.collect(toList());
        Optional.of(doubleList).ifPresent(System.out::println);


        // CompletableFuture的 join() 和 thenApply() 方法使用
        Stream<CompletableFuture<Double>> completableFutureStream2 = integers.stream().map(i -> {
            return CompletableFuture.supplyAsync(() -> CompletableAction3.getProductById(i), executorService);
        });

        Stream<CompletableFuture<Double>> completableFutureStream1 = completableFutureStream.map(future -> {
            return future.thenApply(CompletableAction3::multiply);
        });
        Stream<Double> doubleStream2 = completableFutureStream1.map(CompletableFuture::join);

        List<Double> doubleList2 = doubleStream.collect(toList());
        Optional.of(doubleList2).ifPresent(System.out::println);
    }

    // 模拟取到数据之后进行相关业务操作，这里模拟取到的数据 * 10
    public static Double multiply(Double d) {
        try {
            Thread.sleep(3000);
            return d * 10d;
        } catch (InterruptedException e) {
            e.printStackTrace();
            return null;
        }
    }

    // 模拟根据 ID 查询商品
    public static Double getProductById(int i) {
        Double aDouble = CompletableAction.get();
        System.out.println(aDouble);
        return aDouble;
    }
}

常用api：

package future;

import java.util.Arrays;
import java.util.List;
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;

public class CompletableAction4 {

    public static void main(String[] args) throws InterruptedException {

        ExecutorService executorService = Executors.newFixedThreadPool(2, (r) -> {
           Thread thread = new Thread(r);
           return thread;
        });

        // thenApply()、supplyAsync()、whenComplete() 方法
        CompletableFuture.supplyAsync(() -> 1d)
                .thenApply(CompletableAction3::multiply)
                .whenComplete((v, t) -> {
                    System.out.println(v);
                });

        // thenRun() 方法
        CompletableFuture.supplyAsync(() -> 1)
                .thenRun(() -> {
                    System.out.println("========》 use the thenRun() method");
                });

        // thenAccept() 方法
        CompletableFuture.supplyAsync(() -> 1)
                .thenAccept(r -> {
                    System.out.println("========》 use the thenAccept() method: " + r);
                });

        // thenCompose() 方法
        CompletableFuture.supplyAsync(() -> 1)
                .thenApply(r -> r * 10d)
                .thenCompose(r -> CompletableFuture.supplyAsync(() -> r))
                .thenAccept(r -> {
                    System.out.println("========》 use the thenCompose() method: " + r);
                });

        // thenCombine() 方法， 有返回值
        CompletableFuture.supplyAsync(() -> 1)
                .thenCombine(CompletableFuture.supplyAsync(() -> 2d), (r1, r2) -> {
                    System.out.println("========》 use the thenCombine() method: " + (r1 + r2));
                    return r1 + r2;
                });

        // thenAcceptBoth() 方法，无返回值。和 then Combine() 方法类似，
        CompletableFuture.supplyAsync(()-> 1)
                .thenAcceptBoth(CompletableFuture.supplyAsync(() -> 3d), (r1, r2) -> {
                    System.out.println("========》 use the thenAcceptBoth() method: " + (r1 + r2));
                });

        // runAfterBoth() 方法，直接执行完。只有两个 CompletableFuture 对象实例化完成才返回
        CompletableFuture.supplyAsync(() -> {
//            try {
//                Thread.sleep(2000);
//                System.out.println("sleep 2s");
//            } catch (InterruptedException e) {
//                e.printStackTrace();
//            }
            return 1;
        }).runAfterBoth(CompletableFuture.supplyAsync(() -> {
//            try {
//                Thread.sleep(3000);
//                System.out.println("sleep 3s");
//            } catch (InterruptedException e) {
//                e.printStackTrace();
//            }
            return 2;
        }), () -> System.out.println("========》 use the runAfterBoth() method"));

        // runAfterEither() 方法，直接执行完。只要有一个 CompletableFuture 对象实例化完成就直接返回
        CompletableFuture.supplyAsync(() -> {
//            try {
//                Thread.sleep(2000);
//                System.out.println("sleep 2s");
//            } catch (InterruptedException e) {
//                e.printStackTrace();
//            }
            return 1;
        }).runAfterEither(CompletableFuture.supplyAsync(() -> {
//            try {
//                Thread.sleep(3000);
//                System.out.println("sleep 3s");
//            } catch (InterruptedException e) {
//                e.printStackTrace();
//            }
            return 2;
        }), () -> System.out.println("========》 use the runAfterEither() method"));

        // acceptEither() 方法
        CompletableFuture.supplyAsync(() -> 1)
                .acceptEither(CompletableFuture.supplyAsync(() -> 2), (r1) -> {
                    System.out.println("========》 use the acceptEither() method：" + r1);
                });

        // acceptEither() 方法
        CompletableFuture.supplyAsync(() -> 1)
                .applyToEither(CompletableFuture.supplyAsync(() -> 2), (r1) -> r1 * 10d)
                .whenComplete((v, t) -> {
                    System.out.println("========》 use the applyToEither() method：" + v);
                });

        // allOf() 方法  必须等所有的实例化完，才返回。前提条件是线程没结束
        List<Integer> integers = Arrays.asList(1, 2, 3, 4, 5);
        Stream<CompletableFuture<Integer>> completableFutureStream = integers.stream().map(i -> CompletableFuture.supplyAsync(() -> {
            System.out.println(i);
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return i;
        }));
        List<CompletableFuture<Integer>> completableFutureList = completableFutureStream.collect(toList());
        CompletableFuture[] completableFutures = completableFutureList.toArray(new CompletableFuture[completableFutureList.size()]);

        CompletableFuture.allOf(completableFutures)
                .thenApply(r -> 10d)
                .whenComplete((v, t) -> {
            System.out.println("========》 use the allOf() method：" + v);
            t.printStackTrace();
        });

        // anyOf() 方法, 只要有一个实例化完直接返回，前提条件是线程没结束
        List<Integer> integers2 = Arrays.asList(1, 2, 3, 4, 5);
        Stream<CompletableFuture<Integer>> completableFutureStream2 = integers2.stream().map(i -> CompletableFuture.supplyAsync(() -> {
            System.out.println(i);
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return i;
        }));
        List<CompletableFuture<Integer>> completableFutureList2 = completableFutureStream2.collect(toList());
        CompletableFuture[] completableFutures2 = completableFutureList.toArray(new CompletableFuture[completableFutureList2.size()]);

        CompletableFuture.anyOf(completableFutures2)
                .thenApply(r -> 10d)
                .whenComplete((v, t) -> {
                    System.out.println("========》 use the anyOf() method：" + v);
                });

        Thread.currentThread().join();
    }
}

来源：oschina

链接：https://my.oschina.net/u/3901188/blog/3189204

标签

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completablefuture