CompletableFuture的入门

runAsync 和 supplyAsync

runAsync接受一个Runable的实现，无返回值

CompletableFuture.runAsync(()->System.out.println("无返回结果的运行"));

supplyAsync接受一个Supplier的实现，有返回值

CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {  System.out.println("有返回结果的运行");  retu 1;  });

获取结果的get和join

都是堵塞，直到返回结果
get方法抛出是经过处理的异常，ExecutionException或**InterruptedException **，需要用户手动捕获

try {System.out.println(CompletableFuture.supplyAsync(() -> {System.out.println("有返回结果的运行");retu 1;  }).get());} catch (InterruptedException e) {  e.printStackTrace();} catch (ExecutionException e) {  e.printStackTrace();}

join方法抛出的就不用捕获，是经过包装的**CompletionException **或 CancellationException

System.out.println(CompletableFuture.supplyAsync(() -> {try {TimeUnit.MILLISECONDS.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("有返回结果的运行");retu 1;}).join());

常用方法

获取结果的get\join\getNow

get():一直等待
get(timeout,unit)：等待，除非超时
getNow(valueIfAbsent)：计算完返回计算的结果，未计算完返回默认的结果

CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {try {TimeUnit.SECONDS.sleep(1);;} catch (InterruptedException e) {e.printStackTrace();}retu 1;});System.out.println("立即获取："+completableFuture.getNow(9999));try {TimeUnit.SECONDS.sleep(2);System.out.println("doing");} catch (InterruptedException e) {e.printStackTrace();}System.out.println("等一会获取："+completableFuture.getNow(9999));

join() 同get()

thenApply\handle

执行完前面的，前面返回的结果返回，然后传给后面再，执行完后面任务，一步一步来。

CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {System.out.println("step 1");retu 1;}).thenApply(a -> {System.out.println("step 2");retu a + 2;}).thenApply(a -> {System.out.println("step 3");retu a + 3;});System.out.println(completableFuture.get());

执行结果：

CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {System.out.println("step 1");int a=1/0;retu 1;}).handle((a,b) -> {System.out.println("step 2");if (b!=null) {System.out.println(b.getMessage());retu 0;}retu a + 2;}).handle((a,b) -> {System.out.println("step 3");if (b!=null) {System.out.println(b.getMessage());retu 0;}retu a + 3;});System.out.println(completableFuture.get());

执行结果：

thenApply和handle的区别：
thenApply执行的时候，有异常的则整个执行链会中断，直接抛出异常。

handle有异常也可以往下一步走，根据带的异常参数可以进一步处理

thenAccept

接收前面任务的返回结果，当前节点处理，并不返回结果。

CompletableFuture.supplyAsync(()->{System.out.println("step 1");retu 10;}).thenAccept(a->{System.out.println("res "+a);});

applyToEither

在多个任务段同时执行时，哪个任务段用时最少，就返回哪个

CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {System.out.println("step 1");try {TimeUnit.SECONDS.sleep(1);} catch (InterruptedException e) {e.printStackTrace();}retu 1;}).applyToEither(CompletableFuture.supplyAsync(() -> {System.out.println("step 2");try {TimeUnit.SECONDS.sleep(2);} catch (InterruptedException e) {e.printStackTrace();}retu 2;}), a -> {retu a;});System.out.println(completableFuture.get());

执行结果：

thenCombine

合并多个任务段的返回结果

CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {System.out.println("step 1");retu IntStream.range(1, 11).sum();}).thenCombine(CompletableFuture.supplyAsync(() -> {System.out.println("step 2");retu IntStream.range(11, 21).sum();}), (a, b) -> a + b).thenCombine(CompletableFuture.supplyAsync(() -> {System.out.println("step 3");retu IntStream.range(21, 31).sum();}), (a, b) -> a + b);System.out.println(completableFuture.get());