CompletableFuture
创建
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runAsync
使用
runAsync()运行异步计算 如果你想异步的运行一个后台任务并且不想改任务返回任务东西，这时候可以使用CompletableFuture.runAsync()方法，它持有一个Runnable对象，并返回CompletableFuture。CompletableFuturerunnable_task = CompletableFuture.runAsync(() -> System.out.println("Runnable task")).whenComplete((v, t) -> { //当抛出异常的时候 if (t != null) { t.printStackTrace(); } }); s
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supplyAsync:
使用
supplyAsync()运行一个异步任务并且返回结果 , 它持有supplier并且返回CompletableFuture是通过调用 传入的supplier取得的值的类型。CompletableFuturestringCompletableFuture = CompletableFuture.supplyAsync(() -> "HELLO").whenComplete((v, t) -> { try { TimeUnit.SECONDS.sleep(5); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("whenComplete" + v); }); System.out.println(stringCompletableFuture.get());
转换&&消费
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thenApply&thenAccept:
thenApply接受一个Function接口(接受R返回T)类型参数，并且继续返回CompletableFuture
，对调用者CompletableFuture进行了转换，注意与thenCompose区分， thenAccept接受一个Comsumer(接受T无返回值)类型参数,并且返回CompletableFuture
,可继续进行链式操作，消费。 thenRun接受一个Runnable,该方法不能不能接收来自前面的参数,通常用与链式的结尾
CompletableFuturestringCompletableFuture = CompletableFuture.supplyAsync(() -> "HELLO").whenComplete((v, t) -> { try { TimeUnit.SECONDS.sleep(5); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("whenComplete" + v); }); //thenApply接受一个Function接口(接受R返回T)类型参数，并且继续返回CompletableFuture //thenAccept接受一个Comsumer(接受T无返回值)类型参数,并且返回CompletableFuture ,可继续进行链式操作 //thenAccept接受一个Runnable,该方法不能不能接收来自前面的参数,通常用与链式的结尾 stringCompletableFuture.thenApply(str -> str + "World").thenAccept(System.out::println).thenRun(() -> System.out.println("Done"));
组合：
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thenCompose
thenCompose（）用来连接两个CompletableFuture，是生成一个新的CompletableFuture,并且前一个Future.get()会成为thenCompose的参数/注意与thenApply的区分
private static void thenCompose() { CompletableFuture.supplyAsync(() -> { System.out.println("Start thenCompose 1"); try { TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("End thenCompose 1"); return "HELLO WORLD"; }).thenCompose(i -> CompletableFuture.supplyAsync(() -> { System.out.println("Start thenCompose 2"); try { TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Start thenCompose 2"); return i.length(); })).whenComplete((i, t) -> System.out.println(i)); }
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thenCombine:
combine可以用以接受一个新的Completable和一个BiFunction,调用者和传入的CompletableFuture作为BiFunction的参数,再返回一个CompletableFuture
,可继续操作。 private static void thenCombine() { CompletableFuture.supplyAsync(() -> { System.out.println("start thenCombine 1"); try { TimeUnit.SECONDS.sleep(ThreadLocalRandom.current().nextInt(6)); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("end thenCombine 1"); return "12345"; }).thenCombine(CompletableFuture.supplyAsync(() -> { System.out.println("start thenCombine 2"); try { TimeUnit.SECONDS.sleep(ThreadLocalRandom.current().nextInt(6)); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("end thenCombine 2"); return "6789"; }), (i, j) -> i.length() > j.length()).whenComplete((b, t) -> System.out.println(b)); }
完成时处理：
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whenComplete
接受一个调用者的future.get()以及可能出现的Throwable作为参数,对结果进行消费BiConsumer
CompletableFuture.supplyAsync(() -> { System.out.println("Start work"); sleep(2); System.out.println("End work"); return "res"; }).whenComplete((r, t) -> System.out.println(r));
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exceptionally
倘若出现异常接受异常并进行处理：
CompletableFuture.supplyAsync(() -> { System.out.println("Start work"); //sleep(2); System.out.println("End work"); return "res"; }).whenComplete((r, t) -> { System.out.println(r); if (t == null) { System.out.println("No err"); } });
MORE API
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thenAcceptBoth
该函数接受前面的future.get()作为h参数传入BiConsumer,并接受本参数callable的future.get()作为w参数传入BiConsumer
private static void acceptBoth() { CompletableFuture.supplyAsync(() -> { System.out.println("Start task1"); try { TimeUnit.SECONDS.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } return "Hello"; }).thenAcceptBoth( //该函数接受前面的future.get()作为h参数传入BiConsumer,并接受本参数callable的future.get()作为w参数传入BiConsumer CompletableFuture.supplyAsync(() -> "World"), (h, w) -> System.out.println(h + "-----" + w)); }
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acceptEither
取先完成的结果.但是没完成的任务也将继续执行
private static void acceptEither() { CompletableFuture.supplyAsync(() -> { System.out.println("Start Either1"); try { TimeUnit.SECONDS.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("End Either2"); return "Either1"; }).acceptEither(CompletableFuture.supplyAsync(() -> { System.out.println("Start Either2"); try { TimeUnit.SECONDS.sleep(ThreadLocalRandom.current().nextInt(5)); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("End Either2"); return "Either2"; }), i -> System.out.println("Final result " + i)); }
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runAfterBoth
执行完毕后调用Runnable,不消费
private static void runAfterBoth() { CompletableFuture.supplyAsync(() -> { System.out.println("start RunAfterBoth 1"); try { TimeUnit.SECONDS.sleep(ThreadLocalRandom.current().nextInt(6)); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("end RunAfterBoth 1"); return "Task 1 Result"; }).runAfterBoth(CompletableFuture.supplyAsync(() -> { System.out.println("start RunAfterBoth 2"); try { TimeUnit.SECONDS.sleep(ThreadLocalRandom.current().nextInt(5)); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("end RunAfterBoth 2"); return "Task 2 Result"; }), () -> System.out.println("Done")); }
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getNow
在调用该方法时，如果已经CompleFuture已经计算完成，则返回future.get()的内容，否者直接返回该方法的参数值(缺省)。
private static void getNow() throws InterruptedException { CompletableFuturestringCompletableFuture = CompletableFuture.supplyAsync(() -> { try { TimeUnit.SECONDS.sleep(2); } catch (InterruptedException e) { e.printStackTrace(); } return "Hello"; }); String now = stringCompletableFuture.getNow("NOWWWWWWWWWWWWWWWWWWWWWWWw"); System.out.println(now); //output NOWWWWWWWWWWWWWWWWWWWWWWWw TimeUnit.SECONDS.sleep(3); now = stringCompletableFuture.getNow("NOWWWWWWWWWWWWWWWWWWWWWWWw"); System.out.println(now); //output Hello }
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complete
类似于getNow方法，返回true的时候说明CompletableFuture以及执行完毕，该方法无效，返回false的时候，说明该方法设值成功，CompletableFuture尚未执行完毕，调用future.get()将返回complete的参数值：
private static void complete() throws InterruptedException, ExecutionException { CompletableFuturestringCompletableFuture = CompletableFuture.supplyAsync(() -> { try { TimeUnit.SECONDS.sleep(2); } catch (InterruptedException e) { e.printStackTrace(); } return "World"; }); //通过注释该行来进行两种情况的测试 TimeUnit.SECONDS.sleep(3); stringCompletableFuture.complete("HELLO"); System.out.println(stringCompletableFuture.get()); }
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join
- 用法跟get一样阻塞调用但是join不会抛出异常