1.创建CompletableFuture对象
runAsync方法：它以Runnabel函数式接口类型为参数，计算结果为空。
supplyAsync方法以Supplier<U>函数式接口类型为参数，计算结果类型为U。
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)
2.结果变换
public <U> CompletionStage<U> thenApply(Function<? super T,? extends U> fn);
public <U> CompletionStage<U> thenApplyAsync(Function<? super T,? extends U> fn);
public <U> CompletionStage<U> thenApplyAsync(Function<? super T,? extends U> fn,Executor executor);
String result = CompletableFuture.supplyAsync(()->{
return "hello";
}).thenApplyAsync(v->"world").join();
System.out.println(result); --》world
3.消费结果
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);
CompletableFuture.supplyAsync(()->{
return "hello";
}).thenAccept(v->{
System.out.println("consume: " +v); --->consume: hello
});
4.结合两个CompletionStage的结果，进行转化后返回
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);
需要上一阶段的返回值，并且other代表的CompletionStage也要返回值之后，把这两个返回值，进行转换后返回指定类型的值。
String result = CompletableFuture.supplyAsync(()->{
try {
Thread.sleep(1000);
}catch (InterruptedException e) {
e.printStackTrace();
}
return "hello";
}).thenCombine(CompletableFuture.supplyAsync(()->{
try {
Thread.sleep(2000);
}catch (InterruptedException e) {
e.printStackTrace();
}
return "world";
}),(s1,s2)->{return s1 +"--" + s2;}).join();
System.out.println(result);-->hello--world
5.两个CompletionStage，谁计算的快，就用那个CompletionStage的结果进行下一步的处理
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);
String result = CompletableFuture.supplyAsync(()->{
try {
Thread.sleep(300);
}catch (InterruptedException e) {
e.printStackTrace();
}
return "hello";
}).applyToEitherAsync(CompletableFuture.supplyAsync(() -> {
try {
Thread.sleep(100);
}catch (InterruptedException e) {
e.printStackTrace();
}
return "world";
}), (s)->{return "处理结果最快的是" +s; }
).join();
System.out.println(result);
6.行时出现了异常，可以通过exceptionally进行补偿
public CompletionStage<T> exceptionally(Function<Throwable, ? extends T> fn);
String message =CompletableFuture.supplyAsync(()->{
try {
Thread.sleep(1000);
}catch (InterruptedException e) {
e.printStackTrace();
}
if(true){
throw new RuntimeException("exception is run");
}
return "hello wolrd";
}).exceptionally(e->{
System.out.println(e.getMessage());
return "world hello";
}).join();
System.out.println(message); -->java.lang.RuntimeException: exception is run
world hello
