Java CompletableFuture 入门到精通CompletableFuture 是 Java 8 中引入的一

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Java CompletableFuture

参考：juejin.cn/post/714024…

一、CompletableFuture 介绍

CompletableFuture 是 Java 8 中引入的一个新特性，它提供了一种简单的方法来实现异步编程和任务组合。

二、重点方法

1、创建任务方法

有返回值：
- supplyAsync(Supplier supplier)
- supplyAsync(Supplier supplier, Executor executor)
无返回值
- runAsync(Runnable runnable)
- runAsync(Runnable runnable, Executor executor)

2、结果处理类

处理结果，返回新值
- thenApply(Function<? super T,? extends U> fn);
- thenApplyAsync(Function<? super T,? extends U> fn);
- thenApplyAsync(Function<? super T,? extends U> fn, Executor executor);
消费结果，但不返回值
- thenAccept(Consumer<? super T> action);
- thenAcceptAsync(Consumer<? super T> action);
- thenAcceptAsync(Consumer<? super T> action, Executor executor);
无参，无返回值
- thenRun(Runnable action);
- thenRunAsync(Runnable action);
- thenRunAsync(Runnable action, Executor executor);
处理结果，实现扁平化嵌套
- thenCompose (Function<? super T, ? extends CompletionStage> fn);
- thenComposeAsync (Function<? super T, ? extends CompletionStage> fn);
- thenComposeAsync (Function<? super T, ? extends CompletionStage> fn, Executor executor);

3、任务组合类

两个任务执行完，再执行第三个任务，处理结果，也有返回。T+U→R
- thenCombine (CompletionStage<? extends U> other, BiFunction<? super T,? super U,? extends V> fn);
- thenCombineAsync (CompletionStage<? extends U> other, BiFunction<? super T,? super U,? extends V> fn);
- thenCombineAsync (CompletionStage<? extends U> other, BiFunction<? super T,? super U,? extends V> fn, Executor executor);

两个任务执行完，再执行第三个任务，处理结果，没有返回

thenAcceptBoth(CompletionStage<? extends U> other, BiConsumer<? super T, ? super U> action);
thenAcceptBothAsync(CompletionStage<? extends U> other, BiConsumer<? super T, ? super U> action);
thenAcceptBothAsync(CompletionStage<? extends U> other, BiConsumer<? super T, ? super U> action, Executor executor);

两个任务执行完，再执行第三个，不处理结果，也没有返回

runAfterBoth(CompletionStage<?> other, Runnable action);
runAfterBothAsync(CompletionStage<?> other, Runnable action);
runAfterBothAsync(CompletionStage<?> other, Runnable action, Executor executor);

两个任务只要有一个完成，就执行任务三，不处理结果，也没返回值

runAfterEither(CompletionStage<?> other, Runnable action);
runAfterEitherAsync(CompletionStage<?> other, Runnable action);
runAfterEitherAsync(CompletionStage<?> other, Runnable action, Executor executor);

两个任务只要有一个完成，就执行任务三，处理结果，没有返回值

acceptEither(CompletionStage<? extends T> other, Consumer<? super T> action);
acceptEitherAsync(CompletionStage<? extends T> other, Consumer<? super T> action);
acceptEitherAsync(CompletionStage<? extends T> other, Consumer<? super T> action, Executor executor);

两个任务只要有一个完成，就执行任务三，处理结果，有返回值

applyToEither(CompletionStage<? extends T> other, Function<? super T, U> fn);
applyToEitherAsync(CompletionStage<? extends T> other, Function<? super T, U> fn);
applyToEitherAsync(CompletionStage<? extends T> other, Function<? super T, U> fn, Executor executor);

所有任务完成，适用于并行任务聚合
- allOf(CompletableFuture<?>... cfs)
任一任务完成，就返回结果，适用于竞争场景
- anyOf(CompletableFuture<?>... cfs)

4、异常处理类

处理异常结果，有返回值
- exceptionally(Function<Throwable, ? extends T> fn);
处理正常和异常结果，也有返回值
- handle(BiFunction<? super T, Throwable, ? extends U> fn);

处理正常和异常结果，没有返回

whenComplete(BiConsumer<? super T, ? super Throwable> action);
whenCompleteAsync(BiConsumer<? super T, ? super Throwable> action);
whenCompleteAsync(BiConsumer<? super T, ? super Throwable> action, Executor executor);