CompletableFuture工具类可以帮助实现Java并发编程中的任务编排

以上除了join用于阻塞调用该发放的线程并且接受CompletableFuture的返回值以外其它方法皆有Async异步和Executor指定线程池选项

对于supply,run,apply,accept的区别在于函数式编程的接口类型不同:

• supply: Supplier<T> supplier => T get()
• run:  Runnable runnable => void run()
• apply:  Function<T, R> => apply(T t)
• accept: Consumer<T> => void accept(T t)

对于以上方法，根据接受参数不同分为两类，一类参数接受如supply,run,apply,accept接口的实现类，另一类参数接受新的CompletableFuture:

FunctionInterface	CompletableFuture
supplyAsync	thenCompose
runAsync	thenCombine
thenApply	thenAcceptBoth
thenAccept	runAfterBoth
thenRun	applyToEither
	acceptEither
	runAfterEither

thenCompose用于先执行A再执行B

thenCombine,thenAcceptBoth,runAfterBoth用于A，B同时执行

applyToEither,acceptEither,runAfterEither用于A,B谁先执行完就跳到C

 exceptionally,handle,whenComplete用于在并发编程中处理结果和异常:

exceptionally:

该方法仅处理异常情况：发生异常时，不会把异常抛出，而是由exceptionally处理结果返回

public static CompletableFuture exceptionally(int a, int b){
    return CompletableFuture.supplyAsync(() -> a/b)
            .exceptionally(ex -> {
                System.out.println("ex:\t"+ex.getMessage());
                return 0;
            });
}

handle:

处理上一阶段返回值和异常，不会把异常抛出，而是由handle处理结果返回

public class CreateThread_FutureTask {
    public static void main(String[] args) {
        CompletableFuture<String> ctf = CompletableFuture.supplyAsync(() -> {
            try {
                Thread.sleep(1000);
                return "1";
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }).applyToEither(CompletableFuture.supplyAsync(() -> {
            try {
                Thread.sleep(50);
                return String.valueOf(1/0);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }), str -> {
            return str;
        }).handle((str,ex)->{
            if(ex!=null){
                return ex.getMessage();
            }
            else{
                return str;
            }
        });
        System.out.println(ctf.join());
        System.out.println("主线程能继续执行");
    }
}

whenComplete:

处理上一阶段返回值和异常，会把异常抛出

public static CompletableFuture whenComplete(int a, int b){
    return CompletableFuture.supplyAsync(() -> a/b)
            .whenComplete((result, ex) -> {
                if (null != ex) {
                    System.out.println("whenComplete error:\t"+ex.getMessage());
                }
            });
}

CompletableFuture.allOf和anyOf

allOf：接受CompletableFuture<?>...ctfs，等待全部执行完毕

anyOf：接受CompletableFuture<?>...ctfs，等待任意一个执行完毕

CompletableFuture[] dishes = IntStream.rangeClosed(1, 10)
                .mapToObj(i -> new Dish("菜" + i, 1L))
                .map(dish -> CompletableFuture.runAsync(dish::make))
                .toArray(CompletableFuture[]::new);
CompletableFuture.allOf(dishes).join();
System.out.println("菜全都做好了");