CompletableFuture 使用详解
1、 runAsync 和 supplyAsync方法
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。
- runAsync方法不支持返回值。
- supplyAsync可以支持返回值。
示例
//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);
}
2、计算结果完成时的回调方法
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。
示例
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);
}
3、 thenApply 方法
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
示例
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。
4、 handle 方法
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);
示例
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。
5、 thenAccept 消费处理结果
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);
示例
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。
6、thenRun 方法
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);
示例
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。
7、thenCombine 合并任务
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);
示例
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());
}
8、thenAcceptBoth
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);
示例
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+";");
}
});
}
9、applyToEither 方法
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);
示例
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());
}
10、acceptEither 方法
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);
示例
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);
}
});
}
11、runAfterEither 方法
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);
示例
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。");
}
});
}
12、runAfterBoth
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);
示例
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。");
}
});
}
13、thenCompose 方法
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) ;
示例
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());
}