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CompletableFuture 提供了四个静态方法来创建一个异步操作。
- public static CompletableFuture<Void> runAsync(Runnable runnable)
- public static CompletableFuture<Void> runAsync(Runnable runnable, Executor executor)
- public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier)
- public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier, Executor executor)
没有指定Executor的方法会使用ForkJoinPool.commonPool() 作为它的线程池执行异步代码。如果指定线程池,则使用指定的线程池运行。以下所有的方法都类同。
- //无返回值
- public static void runAsync() throws Exception {
- CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
- try {
- TimeUnit.SECONDS.sleep(1);
- } catch (InterruptedException e) {
- }
- System.out.println("run end ...");
- });
-
- future.get();
- }
-
- //有返回值
- public static void supplyAsync() throws Exception {
- CompletableFuture<Long> future = CompletableFuture.supplyAsync(() -> {
- try {
- TimeUnit.SECONDS.sleep(1);
- } catch (InterruptedException e) {
- }
- System.out.println("run end ...");
- return System.currentTimeMillis();
- });
-
- long time = future.get();
- System.out.println("time = "+time);
- }
当CompletableFuture的计算结果完成,或者抛出异常的时候,可以执行特定的Action。主要是下面的方法:
- public CompletableFuture<T> whenComplete(BiConsumer<? super T,? super Throwable> action)
- public CompletableFuture<T> whenCompleteAsync(BiConsumer<? super T,? super Throwable> action)
- public CompletableFuture<T> whenCompleteAsync(BiConsumer<? super T,? super Throwable> action, Executor executor)
- public CompletableFuture<T> exceptionally(Function<Throwable,? extends T> fn)
可以看到Action的类型是BiConsumer<? super T,? super Throwable>它可以处理正常的计算结果,或者异常情况。
whenComplete 和 whenCompleteAsync 的区别:
whenComplete:是执行当前任务的线程执行继续执行 whenComplete 的任务。
whenCompleteAsync:是执行把 whenCompleteAsync 这个任务继续提交给线程池来进行执行。
- public static void whenComplete() throws Exception {
- CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
- try {
- TimeUnit.SECONDS.sleep(1);
- } catch (InterruptedException e) {
- }
- if(new Random().nextInt()%2>=0) {
- int i = 12/0;
- }
- System.out.println("run end ...");
- });
-
- future.whenComplete(new BiConsumer<Void, Throwable>() {
- @Override
- public void accept(Void t, Throwable action) {
- System.out.println("执行完成!");
- }
-
- });
- future.exceptionally(new Function<Throwable, Void>() {
- @Override
- public Void apply(Throwable t) {
- System.out.println("执行失败!"+t.getMessage());
- return null;
- }
- });
-
- TimeUnit.SECONDS.sleep(2);
- }
当一个线程依赖另一个线程时,可以使用 thenApply 方法来把这两个线程串行化。
- public <U> CompletableFuture<U> thenApply(Function<? super T,? extends U> fn)
- public <U> CompletableFuture<U> thenApplyAsync(Function<? super T,? extends U> fn)
- public <U> CompletableFuture<U> thenApplyAsync(Function<? super T,? extends U> fn, Executor executor)
Function<? super T,? extends U>
T:上一个任务返回结果的类型
U:当前任务的返回值类型
- private static void thenApply() throws Exception {
- CompletableFuture<Long> future = CompletableFuture.supplyAsync(new Supplier<Long>() {
- @Override
- public Long get() {
- long result = new Random().nextInt(100);
- System.out.println("result1="+result);
- return result;
- }
- }).thenApply(new Function<Long, Long>() {
- @Override
- public Long apply(Long t) {
- long result = t*5;
- System.out.println("result2="+result);
- return result;
- }
- });
-
- long result = future.get();
- System.out.println(result);
- }
第二个任务依赖第一个任务的结果。
handle 是执行任务完成时对结果的处理。
handle 方法和 thenApply 方法处理方式基本一样。不同的是 handle 是在任务完成后再执行,还可以处理异常的任务。thenApply 只可以执行正常的任务,任务出现异常则不执行 thenApply 方法。
- public <U> CompletionStage<U> handle(BiFunction<? super T, Throwable, ? extends U> fn);
- public <U> CompletionStage<U> handleAsync(BiFunction<? super T, Throwable, ? extends U> fn);
- public <U> CompletionStage<U> handleAsync(BiFunction<? super T, Throwable, ? extends U> fn,Executor executor);
- public static void handle() throws Exception{
- CompletableFuture<Integer> future = CompletableFuture.supplyAsync(new Supplier<Integer>() {
-
- @Override
- public Integer get() {
- int i= 10/0;
- return new Random().nextInt(10);
- }
- }).handle(new BiFunction<Integer, Throwable, Integer>() {
- @Override
- public Integer apply(Integer param, Throwable throwable) {
- int result = -1;
- if(throwable==null){
- result = param * 2;
- }else{
- System.out.println(throwable.getMessage());
- }
- return result;
- }
- });
- System.out.println(future.get());
- }
从示例中可以看出,在 handle 中可以根据任务是否有异常来进行做相应的后续处理操作。而 thenApply 方法,如果上个任务出现错误,则不会执行 thenApply 方法。
接收任务的处理结果,并消费处理,无返回结果。
- public CompletionStage<Void> thenAccept(Consumer<? super T> action);
- public CompletionStage<Void> thenAcceptAsync(Consumer<? super T> action);
- public CompletionStage<Void> thenAcceptAsync(Consumer<? super T> action,Executor executor);
- public static void thenAccept() throws Exception{
- CompletableFuture<Void> future = CompletableFuture.supplyAsync(new Supplier<Integer>() {
- @Override
- public Integer get() {
- return new Random().nextInt(10);
- }
- }).thenAccept(integer -> {
- System.out.println(integer);
- });
- future.get();
- }
从示例代码中可以看出,该方法只是消费执行完成的任务,并可以根据上面的任务返回的结果进行处理。并没有后续的输错操作。
跟 thenAccept 方法不一样的是,不关心任务的处理结果。只要上面的任务执行完成,就开始执行 thenAccept 。
- public CompletionStage<Void> thenRun(Runnable action);
- public CompletionStage<Void> thenRunAsync(Runnable action);
- public CompletionStage<Void> thenRunAsync(Runnable action,Executor executor);
- public static void thenRun() throws Exception{
- CompletableFuture<Void> future = CompletableFuture.supplyAsync(new Supplier<Integer>() {
- @Override
- public Integer get() {
- return new Random().nextInt(10);
- }
- }).thenRun(() -> {
- System.out.println("thenRun ...");
- });
- future.get();
- }
该方法同 thenAccept 方法类似。不同的是上个任务处理完成后,并不会把计算的结果传给 thenRun 方法。只是处理玩任务后,执行 thenAccept 的后续操作。
thenCombine 会把 两个 CompletionStage 的任务都执行完成后,把两个任务的结果一块交给 thenCombine 来处理。
- public <U,V> CompletionStage<V> thenCombine(CompletionStage<? extends U> other,BiFunction<? super T,? super U,? extends V> fn);
- public <U,V> CompletionStage<V> thenCombineAsync(CompletionStage<? extends U> other,BiFunction<? super T,? super U,? extends V> fn);
- public <U,V> CompletionStage<V> thenCombineAsync(CompletionStage<? extends U> other,BiFunction<? super T,? super U,? extends V> fn,Executor executor);
- private static void thenCombine() throws Exception {
- CompletableFuture<String> future1 = CompletableFuture.supplyAsync(new Supplier<String>() {
- @Override
- public String get() {
- return "hello";
- }
- });
- CompletableFuture<String> future2 = CompletableFuture.supplyAsync(new Supplier<String>() {
- @Override
- public String get() {
- return "hello";
- }
- });
- CompletableFuture<String> result = future1.thenCombine(future2, new BiFunction<String, String, String>() {
- @Override
- public String apply(String t, String u) {
- return t+" "+u;
- }
- });
- System.out.println(result.get());
- }
当两个CompletionStage都执行完成后,把结果一块交给thenAcceptBoth来进行消耗
- public <U> CompletionStage<Void> thenAcceptBoth(CompletionStage<? extends U> other,BiConsumer<? super T, ? super U> action);
- public <U> CompletionStage<Void> thenAcceptBothAsync(CompletionStage<? extends U> other,BiConsumer<? super T, ? super U> action);
- public <U> CompletionStage<Void> thenAcceptBothAsync(CompletionStage<? extends U> other,BiConsumer<? super T, ? super U> action, Executor executor);
-
- private static void thenAcceptBoth() throws Exception {
- CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(new Supplier<Integer>() {
- @Override
- public Integer get() {
- int t = new Random().nextInt(3);
- try {
- TimeUnit.SECONDS.sleep(t);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- System.out.println("f1="+t);
- return t;
- }
- });
-
- CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(new Supplier<Integer>() {
- @Override
- public Integer get() {
- int t = new Random().nextInt(3);
- try {
- TimeUnit.SECONDS.sleep(t);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- System.out.println("f2="+t);
- return t;
- }
- });
- f1.thenAcceptBoth(f2, new BiConsumer<Integer, Integer>() {
- @Override
- public void accept(Integer t, Integer u) {
- System.out.println("f1="+t+";f2="+u+";");
- }
- });
- }
两个CompletionStage,谁执行返回的结果快,我就用那个CompletionStage的结果进行下一步的转化操作。
- public <U> CompletionStage<U> applyToEither(CompletionStage<? extends T> other,Function<? super T, U> fn);
- public <U> CompletionStage<U> applyToEitherAsync(CompletionStage<? extends T> other,Function<? super T, U> fn);
- public <U> CompletionStage<U> applyToEitherAsync(CompletionStage<? extends T> other,Function<? super T, U> fn,Executor executor);
- private static void applyToEither() throws Exception {
- CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(new Supplier<Integer>() {
- @Override
- public Integer get() {
- int t = new Random().nextInt(3);
- try {
- TimeUnit.SECONDS.sleep(t);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- System.out.println("f1="+t);
- return t;
- }
- });
- CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(new Supplier<Integer>() {
- @Override
- public Integer get() {
- int t = new Random().nextInt(3);
- try {
- TimeUnit.SECONDS.sleep(t);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- System.out.println("f2="+t);
- return t;
- }
- });
-
- CompletableFuture<Integer> result = f1.applyToEither(f2, new Function<Integer, Integer>() {
- @Override
- public Integer apply(Integer t) {
- System.out.println(t);
- return t * 2;
- }
- });
-
- System.out.println(result.get());
- }
两个CompletionStage,谁执行返回的结果快,我就用那个CompletionStage的结果进行下一步的消耗操作。
- public CompletionStage<Void> acceptEither(CompletionStage<? extends T> other,Consumer<? super T> action);
- public CompletionStage<Void> acceptEitherAsync(CompletionStage<? extends T> other,Consumer<? super T> action);
- public CompletionStage<Void> acceptEitherAsync(CompletionStage<? extends T> other,Consumer<? super T> action,Executor executor);
- private static void acceptEither() throws Exception {
- CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(new Supplier<Integer>() {
- @Override
- public Integer get() {
- int t = new Random().nextInt(3);
- try {
- TimeUnit.SECONDS.sleep(t);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- System.out.println("f1="+t);
- return t;
- }
- });
-
- CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(new Supplier<Integer>() {
- @Override
- public Integer get() {
- int t = new Random().nextInt(3);
- try {
- TimeUnit.SECONDS.sleep(t);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- System.out.println("f2="+t);
- return t;
- }
- });
- f1.acceptEither(f2, new Consumer<Integer>() {
- @Override
- public void accept(Integer t) {
- System.out.println(t);
- }
- });
- }
两个CompletionStage,任何一个完成了都会执行下一步的操作(Runnable)
- public CompletionStage<Void> runAfterEither(CompletionStage<?> other,Runnable action);
- public CompletionStage<Void> runAfterEitherAsync(CompletionStage<?> other,Runnable action);
- public CompletionStage<Void> runAfterEitherAsync(CompletionStage<?> other,Runnable action,Executor executor);
- private static void runAfterEither() throws Exception {
- CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(new Supplier<Integer>() {
- @Override
- public Integer get() {
- int t = new Random().nextInt(3);
- try {
- TimeUnit.SECONDS.sleep(t);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- System.out.println("f1="+t);
- return t;
- }
- });
-
- CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(new Supplier<Integer>() {
- @Override
- public Integer get() {
- int t = new Random().nextInt(3);
- try {
- TimeUnit.SECONDS.sleep(t);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- System.out.println("f2="+t);
- return t;
- }
- });
- f1.runAfterEither(f2, new Runnable() {
-
- @Override
- public void run() {
- System.out.println("上面有一个已经完成了。");
- }
- });
- }
两个CompletionStage,都完成了计算才会执行下一步的操作(Runnable)
- public CompletionStage<Void> runAfterBoth(CompletionStage<?> other,Runnable action);
- public CompletionStage<Void> runAfterBothAsync(CompletionStage<?> other,Runnable action);
- public CompletionStage<Void> runAfterBothAsync(CompletionStage<?> other,Runnable action,Executor executor);
- private static void runAfterBoth() throws Exception {
- CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(new Supplier<Integer>() {
- @Override
- public Integer get() {
- int t = new Random().nextInt(3);
- try {
- TimeUnit.SECONDS.sleep(t);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- System.out.println("f1="+t);
- return t;
- }
- });
-
- CompletableFuture<Integer> f2 = CompletableFuture.supplyAsync(new Supplier<Integer>() {
- @Override
- public Integer get() {
- int t = new Random().nextInt(3);
- try {
- TimeUnit.SECONDS.sleep(t);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- System.out.println("f2="+t);
- return t;
- }
- });
- f1.runAfterBoth(f2, new Runnable() {
-
- @Override
- public void run() {
- System.out.println("上面两个任务都执行完成了。");
- }
- });
- }
thenCompose 方法允许你对两个 CompletionStage 进行流水线操作,第一个操作完成时,将其结果作为参数传递给第二个操作。
- public <U> CompletableFuture<U> thenCompose(Function<? super T, ? extends CompletionStage<U>> fn);
- public <U> CompletableFuture<U> thenComposeAsync(Function<? super T, ? extends CompletionStage<U>> fn) ;
- public <U> CompletableFuture<U> thenComposeAsync(Function<? super T, ? extends CompletionStage<U>> fn, Executor executor) ;
- private static void thenCompose() throws Exception {
- CompletableFuture<Integer> f = CompletableFuture.supplyAsync(new Supplier<Integer>() {
- @Override
- public Integer get() {
- int t = new Random().nextInt(3);
- System.out.println("t1="+t);
- return t;
- }
- }).thenCompose(new Function<Integer, CompletionStage<Integer>>() {
- @Override
- public CompletionStage<Integer> apply(Integer param) {
- return CompletableFuture.supplyAsync(new Supplier<Integer>() {
- @Override
- public Integer get() {
- int t = param *2;
- System.out.println("t2="+t);
- return t;
- }
- });
- }
-
- });
- System.out.println("thenCompose result : "+f.get());
- }
14、 主线程阻塞等待所有CompletableFuture都完成
-
- CompletableFuture.allOf(todayOrderCountFuture, todayTurnoverFuture, totalTurnoverFuture)
- .thenRun(() -> System.out.println("完成!!!!"))
- .join();
- // 主线程返回
- return result;
作者:jijs
链接:https://www.jianshu.com/p/6bac52527ca4
来源:简书
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