Java1.5引入了Future，CompletableFuture是在1.8引入的。它的出现可以让我们更好的安排任务，合理的使用会大大减少多任务的处理时间，达到事半功倍的目的。下面我们就来看看与它相关的一些知识。1Java中的函数式编程查看CompletableFuture以了解一些Java中的函数式编程会更有用。@FunctionalInterface是Java1.8引入的，在java.util.function包中引入了很多函数式接口。看几个常见的：1.1ConsumerConsumer消费者，关联的方法是voidaccept(Tt)，有参数，无返回值。@FunctionalInterfacepublicinterfaceConsumer{voidaccept(Tt);1.2FunctionFunction函数，关联方法为Rapply(Tt)，有参数和返回值。@FunctionalInterfacepublicinterfaceFunction{Rapply(Tt);1.3PredicatePredicate谓词(assertion?)，关联方法是booleantest(Tt)，有参数和返回值(bool)。@FunctionalInterfacepublicinterfacePredicate{布尔测试(Tt);1.4SupplierSupplier供应商，关联方法为Tget()，无参数和返回值。@FunctionalInterfacepublicinterfaceSupplier{Tget();}2CompletableFuture后续内容将主要关注其内部的各种API。在后续的方法中，由于CompletableFuture实现了CompletionStage，所以具有链式调用的能力。大多数方法将类似于以下内容：xxx(Functionfunc)：与上面相同的线程将执行当前任务xxxAsync(Functionfunc)：将启动一个新线程来执行当前任务xxxAsync(Functionfunc,Executorexecutor)：将使用executor线程池中的新线程执行当前任务2.1CompletableFuture创建supplyAsync：以Supplier为参数，有返回值。publicstaticCompletableFuturesupplyAsync(Suppliersupplier)publicstaticCompletableFuturesupplyAsync(Suppliersupplier,Executorexecutor)runAsync：以Runnable为参数，返回Void。publicstaticCompletableFuturerunAsync(Runnablerunnable)publicstaticCompletableFuturerunAsync(Runnablerunnable,Executorexecutor)completedFuture：创建一个已经具有值的完成的CompletableFuture。publicstaticCompletableFuturecompletedFuture(Uvalue)failedFuture：创建一个已完成但有异常的CompletableFuture。publicstaticCompletableFuturefailedFuture(Throwableex)可以看到runAsync和supplyAsync都额外提供了一个参数Exec??utor。当没有指定executor时，会默认使用ForkJoinPool.commonPool()来执行异步任务，而ParallelStream默认在某些情况下也会使用线程池。如果共享，可能会导致非核心业务抢占核心业务的执行。通常，自定义线程池用于执行这些任务。2.2CompletableFuture的后续操作2.2.1执行一个task(1)apply：有参数和返回值。之前的返回值将作为当前函数的输入。publicCompletableFuturethenApply(Functionfn)publicCompletableFuturethenApplyAsync(Functionfn)publicCompletableFuturethenApplyAsync(Functionfn,Executorexecutor)accept:有参数，无返回值。会将先前的输出作为当前函数的输入。publicCompletableFuturethenAccept(Consumeraction)publicCompletableFuturethenAcceptAsync(Consumeraction)publicCompletableFuturethenAcceptAsync(Consumeraction,Executor执行者)运行：编写另一个无关紧要的任务publicCompletableFuturethenRun(Runnableaction)publicCompletableFuturethenRunAsync(Runnableaction)publicCompletableFuturethenRunAsync(Runnableaction,Executorexecutor)示例@Testexceptionthrowvoid,InterruptedException{finalCompletableFuturefuture=CompletableFuture.supplyAsync(()->1).thenApply((val)->val+1);assertEquals(2,future.get());}@TestvoidtestAccept(){finalCompletableFuturefuture=CompletableFuture.supplyAsync(()->1).thenAccept((val)->{assertEquals(1,val);});future.join();}@TestvoidtestRun(){finalCompletableFuturefuture=CompletableFuture.supplyAsync(()->1).thenRun(()->{});future.join();}2.2.1执行一个任务（2）whenComplete：当任务完成时执行该方法，并将返回值和异常传递给BiConsumer（有参数但无返回值）publicCompletableFuturewhenComplete(BiConsumer动作)publicCompletableFuturewhenCompleteAsync(BiConsumeraction)publicCompletableFuturewhenCompleteAsync(BiConsumeraction,Executorexecutor)exceptionally：当任务发生异常时会调用相应的This方法，并将异常作为参数传入publicCompletableFutureexceptionally(Functionfn)publicCompletableFutureexceptionallyAsync(Functionfn)publicCompletableFutureexceptionallyAsync(Functionfn,Executor执行器)处理程序:接收并处理之前任务的结果BiFunction(带有参数和返回值)publicCompletableFuturehandle(BiFunctionfn)publicCompletableFuturehandleAsync(BiFunctionfn)publicCompletableFuturehandleAsync(BiFunctionfn,Executorexecutor)2.2.2执行两个任务之一即applyToEither：执行两个任务，无一例外地返回其中一个，并将输出作为参数传递给后续的Function（有参数和返回值）publicCompletableFutureapplyToEither(CompletionStageother,Functionfn)publicCompletableFutureapplyToEitherAsync(CompletionStageother,Functionfn)publicCompletableFutureapplyToEitherAsync(CompletionStageother,Functionfn,Executorexecutor)acceptEither：执行两个任务，无一例外地返回其中一个，并将输出作为参数传递给后续的Consumer（有参数但无返回值）)公共完成ableFutureacceptEither(CompletionStageother,Consumeraction)publicCompletableFutureacceptEitherAsync(CompletionStageother,Consumeraction)publicCompletableFutureacceptEitherAsync(CompletionStageother,Consumeraction,Executorexecutor)runAfterEither：执行两个任务，无异常返回其中一个，并将输出作为参数传递给后续的Runnable（无参数，无返回值)publicCompletableFuturerunAfterEither(CompletionStageother,Runnableaction)publicCompletableFuturerunAfterEitherAsync(CompletionStageother,Runnableaction)publicCompletableFuturerunAfterEitherAsync(CompletionStageother,Runnableaction))Executorexecutor)2.2.3执行两个任务完成thenCombine：执行两个任务并将这两个任务作为参数输入到BiFunction中（带参数和返回值）publicCompletableFuturethenCombine(CompletionStage其他，BiFunctionfn)publicCompletableFuturethenCombineAsync(CompletionStageother,BiFunctionfn)publicCompletableFuturethenCombineAsync(CompletionStage<？无返回值)publicCompletableFuturethenAcceptBoth(CompletionStageother,BiConsumeraction)publicCompletableFuturethenAcceptBothAsync(CompletionStageother,BiConsumeraction)publicCompletableFuturethenAcceptBothAsync(CompletionStageother,BiConsumeraction,Executorexecutor)runAfterBoth:Execute两个任务，然后执行Runnable（无参数，无返回值）publicCompletableFuturerunAfterBoth(CompletionStageother,Runnableaction)publicCompletableFuturerunAfterBothAsync(CompletionStageother,Runnableaction)publicCompletableFuturerunAfterBothAsync(CompletionStageother,Runnableaction,Executor)2.2.4执行两个依赖任务thenCompose：前一个任务的结果应该作为参数给第二个任务publicCompletableFuturethenCompose(Function>fn)publicCompletableFuturethenComposeAsync(Function>fn)publicCompletableFuturethenComposeAsync(Function>fn,Executorexecutor)2.2.5合并更多任务allOf：等待所有任务完成publicstaticCompletableFutureallOf(CompletableFuture...cfs)anyOf：等待任何任务完成publicstaticCompletableFuture
