返回顶部
首页 > 资讯 > 后端开发 > JAVA >CompletableFuture使用详解(全网看这一篇就行)
  • 329
分享到

CompletableFuture使用详解(全网看这一篇就行)

java 2023-09-12 09:09:27 329人浏览 独家记忆
摘要

CompletableFuture是jdk8的新特性。CompletableFuture实现了CompletionStage接口和Future接口,前者是对后者的一个扩展,增加了异步会点、流式处理、多个Future组合处理的能力,使Java

CompletableFuture是jdk8的新特性。CompletableFuture实现了CompletionStage接口和Future接口,前者是对后者的一个扩展,增加了异步会点、流式处理、多个Future组合处理的能力,使Java在处理多任务的协同工作时更加顺畅便利。

一、创建异步任务

1. supplyAsync

supplyAsync是创建带有返回值的异步任务。它有如下两个方法,一个是使用默认线程池(ForkJoinPool.commonPool())的方法,一个是带有自定义线程池的重载方法

// 带返回值异步请求,默认线程池public static  CompletableFuture supplyAsync(Supplier supplier)// 带返回值的异步请求,可以自定义线程池public static  CompletableFuture supplyAsync(Supplier supplier, Executor executor)

测试代码:

public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf = CompletableFuture.supplyAsync(() -> {            System.out.println("do something....");            return "result";        });        //等待任务执行完成        System.out.println("结果->" + cf.get());}public static void main(String[] args) throws ExecutionException, InterruptedException {        // 自定义线程池        ExecutorService executorService = Executors.newSingleThreadExecutor();        CompletableFuture cf = CompletableFuture.supplyAsync(() -> {            System.out.println("do something....");            return "result";        }, executorService);        //等待子任务执行完成        System.out.println("结果->" + cf.get());}

 测试结果:

 2. runAsync

runAsync是创建没有返回值的异步任务。它有如下两个方法,一个是使用默认线程池(ForkJoinPool.commonPool())的方法,一个是带有自定义线程池的重载方法

// 不带返回值的异步请求,默认线程池public static CompletableFuture runAsync(Runnable runnable)// 不带返回值的异步请求,可以自定义线程池public static CompletableFuture runAsync(Runnable runnable, Executor executor)

测试代码:

public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf = CompletableFuture.runAsync(() -> {            System.out.println("do something....");        });        //等待任务执行完成        System.out.println("结果->" + cf.get());}public static void main(String[] args) throws ExecutionException, InterruptedException {        // 自定义线程池        ExecutorService executorService = Executors.newSingleThreadExecutor();        CompletableFuture cf = CompletableFuture.runAsync(() -> {            System.out.println("do something....");        }, executorService);        //等待任务执行完成        System.out.println("结果->" + cf.get());}

测试结果:

3.获取任务结果的方法

// 如果完成则返回结果,否则就抛出具体的异常public T get() throws InterruptedException, ExecutionException // 最大时间等待返回结果,否则就抛出具体异常public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException// 完成时返回结果值,否则抛出unchecked异常。为了更好地符合通用函数形式的使用,如果完成此 CompletableFuture所涉及的计算引发异常,则此方法将引发unchecked异常并将底层异常作为其原因public T join()// 如果完成则返回结果值(或抛出任何遇到的异常),否则返回给定的 valueIfAbsent。public T getNow(T valueIfAbsent)// 如果任务没有完成,返回的值设置为给定值public boolean complete(T value)// 如果任务没有完成,就抛出给定异常public boolean completeExceptionally(Throwable ex) 

 二、异步回调处理

1.thenApply和thenApplyAsync

 thenApply 表示某个任务执行完成后执行的动作,即回调方法,会将该任务的执行结果即方法返回值作为入参传递到回调方法中,带有返回值。

测试代码:

public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            System.out.println(Thread.currentThread() + " cf1 do something....");            return 1;        });        CompletableFuture cf2 = cf1.thenApplyAsync((result) -> {            System.out.println(Thread.currentThread() + " cf2 do something....");            result += 2;            return result;        });        //等待任务1执行完成        System.out.println("cf1结果->" + cf1.get());        //等待任务2执行完成        System.out.println("cf2结果->" + cf2.get());}public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            System.out.println(Thread.currentThread() + " cf1 do something....");            return 1;        });        CompletableFuture cf2 = cf1.thenApply((result) -> {            System.out.println(Thread.currentThread() + " cf2 do something....");            result += 2;            return result;        });        //等待任务1执行完成        System.out.println("cf1结果->" + cf1.get());        //等待任务2执行完成        System.out.println("cf2结果->" + cf2.get());}

测试结果:

   

从上面代码和测试结果我们发现thenApply和thenApplyAsync区别在于,使用thenApply方法时子任务与父任务使用的是同一个线程,而thenApplyAsync在子任务中是另起一个线程执行任务,并且thenApplyAsync可以自定义线程池,默认的使用ForkJoinPool.commonPool()线程池。

2.thenAccept和thenAcceptAsync

 thenAccep表示某个任务执行完成后执行的动作,即回调方法,会将该任务的执行结果即方法返回值作为入参传递到回调方法中,无返回值。

测试代码

public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            System.out.println(Thread.currentThread() + " cf1 do something....");            return 1;        });        CompletableFuture cf2 = cf1.thenAccept((result) -> {            System.out.println(Thread.currentThread() + " cf2 do something....");        });        //等待任务1执行完成        System.out.println("cf1结果->" + cf1.get());        //等待任务2执行完成        System.out.println("cf2结果->" + cf2.get());}public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            System.out.println(Thread.currentThread() + " cf1 do something....");            return 1;        });        CompletableFuture cf2 = cf1.thenAcceptAsync((result) -> {            System.out.println(Thread.currentThread() + " cf2 do something....");        });        //等待任务1执行完成        System.out.println("cf1结果->" + cf1.get());        //等待任务2执行完成        System.out.println("cf2结果->" + cf2.get());}

测试结果:

 从上面代码和测试结果我们发现thenAccep和thenAccepAsync区别在于,使用thenAccep方法时子任务与父任务使用的是同一个线程,而thenAccepAsync在子任务中可能是另起一个线程执行任务,并且thenAccepAsync可以自定义线程池,默认的使用ForkJoinPool.commonPool()线程池。

2.thenRun和thenRunAsync

 thenRun表示某个任务执行完成后执行的动作,即回调方法,无入参,无返回值。

测试代码:

public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            System.out.println(Thread.currentThread() + " cf1 do something....");            return 1;        });        CompletableFuture cf2 = cf1.thenRun(() -> {            System.out.println(Thread.currentThread() + " cf2 do something....");        });        //等待任务1执行完成        System.out.println("cf1结果->" + cf1.get());        //等待任务2执行完成        System.out.println("cf2结果->" + cf2.get());}public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            System.out.println(Thread.currentThread() + " cf1 do something....");            return 1;        });        CompletableFuture cf2 = cf1.thenRunAsync(() -> {            System.out.println(Thread.currentThread() + " cf2 do something....");        });        //等待任务1执行完成        System.out.println("cf1结果->" + cf1.get());        //等待任务2执行完成        System.out.println("cf2结果->" + cf2.get());}

 测试结果:

从上面代码和测试结果我们发现thenRun和thenRunAsync区别在于,使用thenRun方法时子任务与父任务使用的是同一个线程,而thenRunAsync在子任务中可能是另起一个线程执行任务,并且thenRunAsync可以自定义线程池,默认的使用ForkJoinPool.commonPool()线程池。

3.whenComplete和whenCompleteAsync

 whenComplete是当某个任务执行完成后执行的回调方法,会将执行结果或者执行期间抛出的异常传递给回调方法,如果是正常执行则异常为null,回调方法对应的CompletableFuture的result和该任务一致,如果该任务正常执行,则get方法返回执行结果,如果是执行异常,则get方法抛出异常。

测试代码:

 public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            System.out.println(Thread.currentThread() + " cf1 do something....");            int a = 1/0;            return 1;        });        CompletableFuture cf2 = cf1.whenComplete((result, e) -> {            System.out.println("上个任务结果:" + result);            System.out.println("上个任务抛出异常:" + e);            System.out.println(Thread.currentThread() + " cf2 do something....");        });//        //等待任务1执行完成//        System.out.println("cf1结果->" + cf1.get());//        //等待任务2执行完成        System.out.println("cf2结果->" + cf2.get());    }

测试结果:

 

 whenCompleteAsync和whenComplete区别也是whenCompleteAsync可能会另起一个线程执行任务,并且thenRunAsync可以自定义线程池,默认的使用ForkJoinPool.commonPool()线程池。

4.handle和handleAsync

 跟whenComplete基本一致,区别在于handle的回调方法有返回值。

测试代码:

public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            System.out.println(Thread.currentThread() + " cf1 do something....");            // int a = 1/0;            return 1;        });        CompletableFuture cf2 = cf1.handle((result, e) -> {            System.out.println(Thread.currentThread() + " cf2 do something....");            System.out.println("上个任务结果:" + result);            System.out.println("上个任务抛出异常:" + e);            return result+2;        });        //等待任务2执行完成        System.out.println("cf2结果->" + cf2.get());}

测试结果 :

三、多任务组合处理 

1.thenCombine、thenAcceptBoth 和runAfterBoth

这三个方法都是将两个CompletableFuture组合起来处理,只有两个任务都正常完成时,才进行下阶段任务。

区别:thenCombine会将两个任务的执行结果作为所提供函数的参数,且该方法有返回值;thenAcceptBoth同样将两个任务的执行结果作为方法入参,但是无返回值;runAfterBoth没有入参,也没有返回值。注意两个任务中只要有一个执行异常,则将该异常信息作为指定任务的执行结果。

测试代码:

public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            System.out.println(Thread.currentThread() + " cf1 do something....");            return 1;        });        CompletableFuture cf2 = CompletableFuture.supplyAsync(() -> {            System.out.println(Thread.currentThread() + " cf2 do something....");            return 2;        });        CompletableFuture cf3 = cf1.thenCombine(cf2, (a, b) -> {            System.out.println(Thread.currentThread() + " cf3 do something....");            return a + b;        });        System.out.println("cf3结果->" + cf3.get());} public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            System.out.println(Thread.currentThread() + " cf1 do something....");            return 1;        });        CompletableFuture cf2 = CompletableFuture.supplyAsync(() -> {            System.out.println(Thread.currentThread() + " cf2 do something....");            return 2;        });                CompletableFuture cf3 = cf1.thenAcceptBoth(cf2, (a, b) -> {            System.out.println(Thread.currentThread() + " cf3 do something....");            System.out.println(a + b);        });        System.out.println("cf3结果->" + cf3.get());}public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            System.out.println(Thread.currentThread() + " cf1 do something....");            return 1;        });        CompletableFuture cf2 = CompletableFuture.supplyAsync(() -> {            System.out.println(Thread.currentThread() + " cf2 do something....");            return 2;        });        CompletableFuture cf3 = cf1.runAfterBoth(cf2, () -> {            System.out.println(Thread.currentThread() + " cf3 do something....");        });        System.out.println("cf3结果->" + cf3.get());}

测试结果:

 

 2.applyToEither、acceptEither和runAfterEither

这三个方法和上面一样也是将两个CompletableFuture组合起来处理,当有一个任务正常完成时,就会进行下阶段任务。

区别:applyToEither会将已经完成任务的执行结果作为所提供函数的参数,且该方法有返回值;acceptEither同样将已经完成任务的执行结果作为方法入参,但是无返回值;runAfterEither没有入参,也没有返回值。

测试代码:

public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            try {                System.out.println(Thread.currentThread() + " cf1 do something....");                Thread.sleep(2000);            } catch (InterruptedException e) {                e.printStackTrace();            }            return "cf1 任务完成";        });        CompletableFuture cf2 = CompletableFuture.supplyAsync(() -> {            try {                System.out.println(Thread.currentThread() + " cf2 do something....");                Thread.sleep(5000);            } catch (InterruptedException e) {                e.printStackTrace();            }            return "cf2 任务完成";        });        CompletableFuture cf3 = cf1.applyToEither(cf2, (result) -> {            System.out.println("接收到" + result);            System.out.println(Thread.currentThread() + " cf3 do something....");            return "cf3 任务完成";        });        System.out.println("cf3结果->" + cf3.get());}public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            try {                System.out.println(Thread.currentThread() + " cf1 do something....");                Thread.sleep(2000);            } catch (InterruptedException e) {                e.printStackTrace();            }            return "cf1 任务完成";        });        CompletableFuture cf2 = CompletableFuture.supplyAsync(() -> {            try {                System.out.println(Thread.currentThread() + " cf2 do something....");                Thread.sleep(5000);            } catch (InterruptedException e) {                e.printStackTrace();            }            return "cf2 任务完成";        });        CompletableFuture cf3 = cf1.acceptEither(cf2, (result) -> {            System.out.println("接收到" + result);            System.out.println(Thread.currentThread() + " cf3 do something....");        });        System.out.println("cf3结果->" + cf3.get());}public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            try {                System.out.println(Thread.currentThread() + " cf1 do something....");                Thread.sleep(2000);            } catch (InterruptedException e) {                e.printStackTrace();            }            System.out.println("cf1 任务完成");            return "cf1 任务完成";        });        CompletableFuture cf2 = CompletableFuture.supplyAsync(() -> {            try {                System.out.println(Thread.currentThread() + " cf2 do something....");                Thread.sleep(5000);            } catch (InterruptedException e) {                e.printStackTrace();            }            System.out.println("cf2 任务完成");            return "cf2 任务完成";        });        CompletableFuture cf3 = cf1.runAfterEither(cf2, () -> {            System.out.println(Thread.currentThread() + " cf3 do something....");            System.out.println("cf3 任务完成");        });        System.out.println("cf3结果->" + cf3.get());}

测试结果: 

从上面可以看出cf1任务完成需要2秒,cf2任务完成需要5秒,使用applyToEither组合两个任务时,只要有其中一个任务完成时,就会执行cf3任务,显然cf1任务先完成了并且将自己任务的结果传值给了cf3任务,cf3任务中打印了接收到cf1任务完成,接着完成自己的任务,并返回cf3任务完成;acceptEither和runAfterEither类似,acceptEither会将cf1任务的结果作为cf3任务的入参,但cf3任务完成时并无返回值;runAfterEither不会将cf1任务的结果作为cf3任务的入参,它是没有任务入参,执行完自己的任务后也并无返回值。

3.allOf / anyOf 

allOf:CompletableFuture是多个任务都执行完成后才会执行,只有有一个任务执行异常,则返回的CompletableFuture执行get方法时会抛出异常,如果都是正常执行,则get返回null。

anyOf :CompletableFuture是多个任务只要有一个任务执行完成,则返回的CompletableFuture执行get方法时会抛出异常,如果都是正常执行,则get返回执行完成任务的结果。

测试代码:

public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            try {                System.out.println(Thread.currentThread() + " cf1 do something....");                Thread.sleep(2000);            } catch (InterruptedException e) {                e.printStackTrace();            }            System.out.println("cf1 任务完成");            return "cf1 任务完成";        });        CompletableFuture cf2 = CompletableFuture.supplyAsync(() -> {            try {                System.out.println(Thread.currentThread() + " cf2 do something....");                int a = 1/0;                Thread.sleep(5000);            } catch (InterruptedException e) {                e.printStackTrace();            }            System.out.println("cf2 任务完成");            return "cf2 任务完成";        });        CompletableFuture cf3 = CompletableFuture.supplyAsync(() -> {            try {                System.out.println(Thread.currentThread() + " cf2 do something....");                Thread.sleep(3000);            } catch (InterruptedException e) {                e.printStackTrace();            }            System.out.println("cf3 任务完成");            return "cf3 任务完成";        });        CompletableFuture cfAll = CompletableFuture.allOf(cf1, cf2, cf3);        System.out.println("cfAll结果->" + cfAll.get());}public static void main(String[] args) throws ExecutionException, InterruptedException {        CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {            try {                System.out.println(Thread.currentThread() + " cf1 do something....");                Thread.sleep(2000);            } catch (InterruptedException e) {                e.printStackTrace();            }            System.out.println("cf1 任务完成");            return "cf1 任务完成";        });        CompletableFuture cf2 = CompletableFuture.supplyAsync(() -> {            try {                System.out.println(Thread.currentThread() + " cf2 do something....");                Thread.sleep(5000);            } catch (InterruptedException e) {                e.printStackTrace();            }            System.out.println("cf2 任务完成");            return "cf2 任务完成";        });        CompletableFuture cf3 = CompletableFuture.supplyAsync(() -> {            try {                System.out.println(Thread.currentThread() + " cf2 do something....");                Thread.sleep(3000);            } catch (InterruptedException e) {                e.printStackTrace();            }            System.out.println("cf3 任务完成");            return "cf3 任务完成";        });        CompletableFuture cfAll = CompletableFuture.anyOf(cf1, cf2, cf3);        System.out.println("cfAll结果->" + cfAll.get());} 

测试结果:

 

来源地址:https://blog.csdn.net/zsx_xiaoxin/article/details/123898171

--结束END--

本文标题: CompletableFuture使用详解(全网看这一篇就行)

本文链接: https://www.lsjlt.com/news/404274.html(转载时请注明来源链接)

有问题或投稿请发送至: 邮箱/279061341@qq.com    QQ/279061341

猜你喜欢
软考高级职称资格查询
编程网,编程工程师的家园,是目前国内优秀的开源技术社区之一,形成了由开源软件库、代码分享、资讯、协作翻译、讨论区和博客等几大频道内容,为IT开发者提供了一个发现、使用、并交流开源技术的平台。
  • 官方手机版

  • 微信公众号

  • 商务合作