Module java.base

Class CompletableFuture<T>

java.lang.Object
java.util.concurrent.CompletableFuture<T>
Type Parameters:
T - The result type returned by this future's join and get methods
All Implemented Interfaces:
CompletionStage<T>, Future<T>

public class CompletableFuture<T> extends Object implements Future<T>, CompletionStage<T>
A Future that may be explicitly completed (setting its value and status), and may be used as a CompletionStage, supporting dependent functions and actions that trigger upon its completion.

When two or more threads attempt to complete, completeExceptionally, or cancel a CompletableFuture, only one of them succeeds.

In addition to these and related methods for directly manipulating status and results, CompletableFuture implements interface CompletionStage with the following policies:

  • Actions supplied for dependent completions of non-async methods may be performed by the thread that completes the current CompletableFuture, or by any other caller of a completion method.
  • All async methods without an explicit Executor argument are performed using the ForkJoinPool.commonPool() (unless it does not support a parallelism level of at least two, in which case, a new Thread is created to run each task). This may be overridden for non-static methods in subclasses by defining method defaultExecutor(). To simplify monitoring, debugging, and tracking, all generated asynchronous tasks are instances of the marker interface CompletableFuture.AsynchronousCompletionTask. Operations with time-delays can use adapter methods defined in this class, for example: supplyAsync(supplier, delayedExecutor(timeout, timeUnit)). To support methods with delays and timeouts, this class maintains at most one daemon thread for triggering and cancelling actions, not for running them.
  • All CompletionStage methods are implemented independently of other public methods, so the behavior of one method is not impacted by overrides of others in subclasses.
  • All CompletionStage methods return CompletableFutures. To restrict usages to only those methods defined in interface CompletionStage, use method minimalCompletionStage(). Or to ensure only that clients do not themselves modify a future, use method copy().

CompletableFuture also implements Future with the following policies:

  • Since (unlike FutureTask) this class has no direct control over the computation that causes it to be completed, cancellation is treated as just another form of exceptional completion. Method cancel has the same effect as completeExceptionally(new CancellationException()). Method isCompletedExceptionally() can be used to determine if a CompletableFuture completed in any exceptional fashion.
  • In case of exceptional completion with a CompletionException, methods get() and get(long, TimeUnit) throw an ExecutionException with the same cause as held in the corresponding CompletionException. To simplify usage in most contexts, this class also defines methods join() and getNow(T) that instead throw the CompletionException directly in these cases.

Arguments used to pass a completion result (that is, for parameters of type T) for methods accepting them may be null, but passing a null value for any other parameter will result in a NullPointerException being thrown.

Subclasses of this class should normally override the "virtual constructor" method newIncompleteFuture(), which establishes the concrete type returned by CompletionStage methods. For example, here is a class that substitutes a different default Executor and disables the obtrude methods:

 
 class MyCompletableFuture<T> extends CompletableFuture<T> {
   static final Executor myExecutor = ...;
   public MyCompletableFuture() { }
   public <U> CompletableFuture<U> newIncompleteFuture() {
     return new MyCompletableFuture<U>(); }
   public Executor defaultExecutor() {
     return myExecutor; }
   public void obtrudeValue(T value) {
     throw new UnsupportedOperationException(); }
   public void obtrudeException(Throwable ex) {
     throw new UnsupportedOperationException(); }
 }
Since:
1.8
  • Constructor Details

    • CompletableFuture

      public CompletableFuture()
      Creates a new incomplete CompletableFuture.
  • Method Details

    • supplyAsync

      public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier)
      Returns a new CompletableFuture that is asynchronously completed by a task running in the ForkJoinPool.commonPool() with the value obtained by calling the given Supplier.
      Type Parameters:
      U - the function's return type
      Parameters:
      supplier - a function returning the value to be used to complete the returned CompletableFuture
      Returns:
      the new CompletableFuture
    • supplyAsync

      public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier, Executor executor)
      Returns a new CompletableFuture that is asynchronously completed by a task running in the given executor with the value obtained by calling the given Supplier.
      Type Parameters:
      U - the function's return type
      Parameters:
      supplier - a function returning the value to be used to complete the returned CompletableFuture
      executor - the executor to use for asynchronous execution
      Returns:
      the new CompletableFuture
    • runAsync

      public static CompletableFuture<Void> runAsync(Runnable runnable)
      Returns a new CompletableFuture that is asynchronously completed by a task running in the ForkJoinPool.commonPool() after it runs the given action.
      Parameters:
      runnable - the action to run before completing the returned CompletableFuture
      Returns:
      the new CompletableFuture
    • runAsync

      public static CompletableFuture<Void> runAsync(Runnable runnable, Executor executor)
      Returns a new CompletableFuture that is asynchronously completed by a task running in the given executor after it runs the given action.
      Parameters:
      runnable - the action to run before completing the returned CompletableFuture
      executor - the executor to use for asynchronous execution
      Returns:
      the new CompletableFuture
    • completedFuture

      public static <U> CompletableFuture<U> completedFuture(U value)
      Returns a new CompletableFuture that is already completed with the given value.
      Type Parameters:
      U - the type of the value
      Parameters:
      value - the value
      Returns:
      the completed CompletableFuture
    • isDone

      public boolean isDone()
      Returns true if completed in any fashion: normally, exceptionally, or via cancellation.
      Specified by:
      isDone in interface Future<T>
      Returns:
      true if completed
    • get

      Waits if necessary for this future to complete, and then returns its result.
      Specified by:
      get in interface Future<T>
      Returns:
      the result value
      Throws:
      CancellationException - if this future was cancelled
      ExecutionException - if this future completed exceptionally
      InterruptedException - if the current thread was interrupted while waiting
    • get

      public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException
      Waits if necessary for at most the given time for this future to complete, and then returns its result, if available.
      Specified by:
      get in interface Future<T>
      Parameters:
      timeout - the maximum time to wait
      unit - the time unit of the timeout argument
      Returns:
      the result value
      Throws:
      CancellationException - if this future was cancelled
      ExecutionException - if this future completed exceptionally
      InterruptedException - if the current thread was interrupted while waiting
      TimeoutException - if the wait timed out
    • join

      public T join()
      Returns the result value when complete, or throws an (unchecked) exception if completed exceptionally. To better conform with the use of common functional forms, if a computation involved in the completion of this CompletableFuture threw an exception, this method throws an (unchecked) CompletionException with the underlying exception as its cause.
      Specified by:
      join in interface Future<T>
      Returns:
      the result value
      Throws:
      CancellationException - if the computation was cancelled
      CompletionException - if this future completed exceptionally or a completion computation threw an exception
    • getNow

      public T getNow(T valueIfAbsent)
      Returns the result value (or throws any encountered exception) if completed, else returns the given valueIfAbsent.
      Parameters:
      valueIfAbsent - the value to return if not completed
      Returns:
      the result value, if completed, else the given valueIfAbsent
      Throws:
      CancellationException - if the computation was cancelled
      CompletionException - if this future completed exceptionally or a completion computation threw an exception
    • complete

      public boolean complete(T value)
      If not already completed, sets the value returned by get() and related methods to the given value.
      Parameters:
      value - the result value
      Returns:
      true if this invocation caused this CompletableFuture to transition to a completed state, else false
    • completeExceptionally

      public boolean completeExceptionally(Throwable ex)
      If not already completed, causes invocations of get() and related methods to throw the given exception.
      Parameters:
      ex - the exception
      Returns:
      true if this invocation caused this CompletableFuture to transition to a completed state, else false
    • thenApply

      public <U> CompletableFuture<U> thenApply(Function<? super T,​? extends U> fn)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this stage completes normally, is executed with this stage's result as the argument to the supplied function.

      This method is analogous to Optional.map and Stream.map.

      See the CompletionStage documentation for rules covering exceptional completion.

      Specified by:
      thenApply in interface CompletionStage<T>
      Type Parameters:
      U - the function's return type
      Parameters:
      fn - the function to use to compute the value of the returned CompletionStage
      Returns:
      the new CompletionStage
    • thenApplyAsync

      public <U> CompletableFuture<U> thenApplyAsync(Function<? super T,​? extends U> fn)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this stage completes normally, is executed using this stage's default asynchronous execution facility, with this stage's result as the argument to the supplied function. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      thenApplyAsync in interface CompletionStage<T>
      Type Parameters:
      U - the function's return type
      Parameters:
      fn - the function to use to compute the value of the returned CompletionStage
      Returns:
      the new CompletionStage
    • thenApplyAsync

      public <U> CompletableFuture<U> thenApplyAsync(Function<? super T,​? extends U> fn, Executor executor)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this stage completes normally, is executed using the supplied Executor, with this stage's result as the argument to the supplied function. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      thenApplyAsync in interface CompletionStage<T>
      Type Parameters:
      U - the function's return type
      Parameters:
      fn - the function to use to compute the value of the returned CompletionStage
      executor - the executor to use for asynchronous execution
      Returns:
      the new CompletionStage
    • thenAccept

      public CompletableFuture<Void> thenAccept(Consumer<? super T> action)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this stage completes normally, is executed with this stage's result as the argument to the supplied action. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      thenAccept in interface CompletionStage<T>
      Parameters:
      action - the action to perform before completing the returned CompletionStage
      Returns:
      the new CompletionStage
    • thenAcceptAsync

      public CompletableFuture<Void> thenAcceptAsync(Consumer<? super T> action)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this stage completes normally, is executed using this stage's default asynchronous execution facility, with this stage's result as the argument to the supplied action. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      thenAcceptAsync in interface CompletionStage<T>
      Parameters:
      action - the action to perform before completing the returned CompletionStage
      Returns:
      the new CompletionStage
    • thenAcceptAsync

      public CompletableFuture<Void> thenAcceptAsync(Consumer<? super T> action, Executor executor)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this stage completes normally, is executed using the supplied Executor, with this stage's result as the argument to the supplied action. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      thenAcceptAsync in interface CompletionStage<T>
      Parameters:
      action - the action to perform before completing the returned CompletionStage
      executor - the executor to use for asynchronous execution
      Returns:
      the new CompletionStage
    • thenRun

      public CompletableFuture<Void> thenRun(Runnable action)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this stage completes normally, executes the given action. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      thenRun in interface CompletionStage<T>
      Parameters:
      action - the action to perform before completing the returned CompletionStage
      Returns:
      the new CompletionStage
    • thenRunAsync

      public CompletableFuture<Void> thenRunAsync(Runnable action)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this stage completes normally, executes the given action using this stage's default asynchronous execution facility. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      thenRunAsync in interface CompletionStage<T>
      Parameters:
      action - the action to perform before completing the returned CompletionStage
      Returns:
      the new CompletionStage
    • thenRunAsync

      public CompletableFuture<Void> thenRunAsync(Runnable action, Executor executor)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this stage completes normally, executes the given action using the supplied Executor. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      thenRunAsync in interface CompletionStage<T>
      Parameters:
      action - the action to perform before completing the returned CompletionStage
      executor - the executor to use for asynchronous execution
      Returns:
      the new CompletionStage
    • thenCombine

      public <U,​ V> CompletableFuture<V> thenCombine(CompletionStage<? extends U> other, BiFunction<? super T,​? super U,​? extends V> fn)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this and the other given stage both complete normally, is executed with the two results as arguments to the supplied function. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      thenCombine in interface CompletionStage<T>
      Type Parameters:
      U - the type of the other CompletionStage's result
      V - the function's return type
      Parameters:
      other - the other CompletionStage
      fn - the function to use to compute the value of the returned CompletionStage
      Returns:
      the new CompletionStage
    • thenCombineAsync

      public <U,​ V> CompletableFuture<V> thenCombineAsync(CompletionStage<? extends U> other, BiFunction<? super T,​? super U,​? extends V> fn)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this and the other given stage both complete normally, is executed using this stage's default asynchronous execution facility, with the two results as arguments to the supplied function. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      thenCombineAsync in interface CompletionStage<T>
      Type Parameters:
      U - the type of the other CompletionStage's result
      V - the function's return type
      Parameters:
      other - the other CompletionStage
      fn - the function to use to compute the value of the returned CompletionStage
      Returns:
      the new CompletionStage
    • thenCombineAsync

      public <U,​ V> CompletableFuture<V> thenCombineAsync(CompletionStage<? extends U> other, BiFunction<? super T,​? super U,​? extends V> fn, Executor executor)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this and the other given stage both complete normally, is executed using the supplied executor, with the two results as arguments to the supplied function. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      thenCombineAsync in interface CompletionStage<T>
      Type Parameters:
      U - the type of the other CompletionStage's result
      V - the function's return type
      Parameters:
      other - the other CompletionStage
      fn - the function to use to compute the value of the returned CompletionStage
      executor - the executor to use for asynchronous execution
      Returns:
      the new CompletionStage
    • thenAcceptBoth

      public <U> CompletableFuture<Void> thenAcceptBoth(CompletionStage<? extends U> other, BiConsumer<? super T,​? super U> action)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this and the other given stage both complete normally, is executed with the two results as arguments to the supplied action. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      thenAcceptBoth in interface CompletionStage<T>
      Type Parameters:
      U - the type of the other CompletionStage's result
      Parameters:
      other - the other CompletionStage
      action - the action to perform before completing the returned CompletionStage
      Returns:
      the new CompletionStage
    • thenAcceptBothAsync

      public <U> CompletableFuture<Void> thenAcceptBothAsync(CompletionStage<? extends U> other, BiConsumer<? super T,​? super U> action)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this and the other given stage both complete normally, is executed using this stage's default asynchronous execution facility, with the two results as arguments to the supplied action. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      thenAcceptBothAsync in interface CompletionStage<T>
      Type Parameters:
      U - the type of the other CompletionStage's result
      Parameters:
      other - the other CompletionStage
      action - the action to perform before completing the returned CompletionStage
      Returns:
      the new CompletionStage
    • thenAcceptBothAsync

      public <U> CompletableFuture<Void> thenAcceptBothAsync(CompletionStage<? extends U> other, BiConsumer<? super T,​? super U> action, Executor executor)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this and the other given stage both complete normally, is executed using the supplied executor, with the two results as arguments to the supplied action. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      thenAcceptBothAsync in interface CompletionStage<T>
      Type Parameters:
      U - the type of the other CompletionStage's result
      Parameters:
      other - the other CompletionStage
      action - the action to perform before completing the returned CompletionStage
      executor - the executor to use for asynchronous execution
      Returns:
      the new CompletionStage
    • runAfterBoth

      public CompletableFuture<Void> runAfterBoth(CompletionStage<?> other, Runnable action)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this and the other given stage both complete normally, executes the given action. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      runAfterBoth in interface CompletionStage<T>
      Parameters:
      other - the other CompletionStage
      action - the action to perform before completing the returned CompletionStage
      Returns:
      the new CompletionStage
    • runAfterBothAsync

      public CompletableFuture<Void> runAfterBothAsync(CompletionStage<?> other, Runnable action)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this and the other given stage both complete normally, executes the given action using this stage's default asynchronous execution facility. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      runAfterBothAsync in interface CompletionStage<T>
      Parameters:
      other - the other CompletionStage
      action - the action to perform before completing the returned CompletionStage
      Returns:
      the new CompletionStage
    • runAfterBothAsync

      public CompletableFuture<Void> runAfterBothAsync(CompletionStage<?> other, Runnable action, Executor executor)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this and the other given stage both complete normally, executes the given action using the supplied executor. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      runAfterBothAsync in interface CompletionStage<T>
      Parameters:
      other - the other CompletionStage
      action - the action to perform before completing the returned CompletionStage
      executor - the executor to use for asynchronous execution
      Returns:
      the new CompletionStage
    • applyToEither

      public <U> CompletableFuture<U> applyToEither(CompletionStage<? extends T> other, Function<? super T,​U> fn)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed with the corresponding result as argument to the supplied function. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      applyToEither in interface CompletionStage<T>
      Type Parameters:
      U - the function's return type
      Parameters:
      other - the other CompletionStage
      fn - the function to use to compute the value of the returned CompletionStage
      Returns:
      the new CompletionStage
    • applyToEitherAsync

      public <U> CompletableFuture<U> applyToEitherAsync(CompletionStage<? extends T> other, Function<? super T,​U> fn)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed using this stage's default asynchronous execution facility, with the corresponding result as argument to the supplied function. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      applyToEitherAsync in interface CompletionStage<T>
      Type Parameters:
      U - the function's return type
      Parameters:
      other - the other CompletionStage
      fn - the function to use to compute the value of the returned CompletionStage
      Returns:
      the new CompletionStage
    • applyToEitherAsync

      public <U> CompletableFuture<U> applyToEitherAsync(CompletionStage<? extends T> other, Function<? super T,​U> fn, Executor executor)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed using the supplied executor, with the corresponding result as argument to the supplied function. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      applyToEitherAsync in interface CompletionStage<T>
      Type Parameters:
      U - the function's return type
      Parameters:
      other - the other CompletionStage
      fn - the function to use to compute the value of the returned CompletionStage
      executor - the executor to use for asynchronous execution
      Returns:
      the new CompletionStage
    • acceptEither

      public CompletableFuture<Void> acceptEither(CompletionStage<? extends T> other, Consumer<? super T> action)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed with the corresponding result as argument to the supplied action. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      acceptEither in interface CompletionStage<T>
      Parameters:
      other - the other CompletionStage
      action - the action to perform before completing the returned CompletionStage
      Returns:
      the new CompletionStage
    • acceptEitherAsync

      public CompletableFuture<Void> acceptEitherAsync(CompletionStage<? extends T> other, Consumer<? super T> action)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed using this stage's default asynchronous execution facility, with the corresponding result as argument to the supplied action. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      acceptEitherAsync in interface CompletionStage<T>
      Parameters:
      other - the other CompletionStage
      action - the action to perform before completing the returned CompletionStage
      Returns:
      the new CompletionStage
    • acceptEitherAsync

      public CompletableFuture<Void> acceptEitherAsync(CompletionStage<? extends T> other, Consumer<? super T> action, Executor executor)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when either this or the other given stage complete normally, is executed using the supplied executor, with the corresponding result as argument to the supplied action. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      acceptEitherAsync in interface CompletionStage<T>
      Parameters:
      other - the other CompletionStage
      action - the action to perform before completing the returned CompletionStage
      executor - the executor to use for asynchronous execution
      Returns:
      the new CompletionStage
    • runAfterEither

      public CompletableFuture<Void> runAfterEither(CompletionStage<?> other, Runnable action)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when either this or the other given stage complete normally, executes the given action. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      runAfterEither in interface CompletionStage<T>
      Parameters:
      other - the other CompletionStage
      action - the action to perform before completing the returned CompletionStage
      Returns:
      the new CompletionStage
    • runAfterEitherAsync

      public CompletableFuture<Void> runAfterEitherAsync(CompletionStage<?> other, Runnable action)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when either this or the other given stage complete normally, executes the given action using this stage's default asynchronous execution facility. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      runAfterEitherAsync in interface CompletionStage<T>
      Parameters:
      other - the other CompletionStage
      action - the action to perform before completing the returned CompletionStage
      Returns:
      the new CompletionStage
    • runAfterEitherAsync

      public CompletableFuture<Void> runAfterEitherAsync(CompletionStage<?> other, Runnable action, Executor executor)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when either this or the other given stage complete normally, executes the given action using the supplied executor. See the CompletionStage documentation for rules covering exceptional completion.
      Specified by:
      runAfterEitherAsync in interface CompletionStage<T>
      Parameters:
      other - the other CompletionStage
      action - the action to perform before completing the returned CompletionStage
      executor - the executor to use for asynchronous execution
      Returns:
      the new CompletionStage
    • thenCompose

      public <U> CompletableFuture<U> thenCompose(Function<? super T,​? extends CompletionStage<U>> fn)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that is completed with the same value as the CompletionStage returned by the given function.

      When this stage completes normally, the given function is invoked with this stage's result as the argument, returning another CompletionStage. When that stage completes normally, the CompletionStage returned by this method is completed with the same value.

      To ensure progress, the supplied function must arrange eventual completion of its result.

      This method is analogous to Optional.flatMap and Stream.flatMap.

      See the CompletionStage documentation for rules covering exceptional completion.

      Specified by:
      thenCompose in interface CompletionStage<T>
      Type Parameters:
      U - the type of the returned CompletionStage's result
      Parameters:
      fn - the function to use to compute another CompletionStage
      Returns:
      the new CompletionStage
    • thenComposeAsync

      public <U> CompletableFuture<U> thenComposeAsync(Function<? super T,​? extends CompletionStage<U>> fn)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that is completed with the same value as the CompletionStage returned by the given function, executed using this stage's default asynchronous execution facility.

      When this stage completes normally, the given function is invoked with this stage's result as the argument, returning another CompletionStage. When that stage completes normally, the CompletionStage returned by this method is completed with the same value.

      To ensure progress, the supplied function must arrange eventual completion of its result.

      See the CompletionStage documentation for rules covering exceptional completion.

      Specified by:
      thenComposeAsync in interface CompletionStage<T>
      Type Parameters:
      U - the type of the returned CompletionStage's result
      Parameters:
      fn - the function to use to compute another CompletionStage
      Returns:
      the new CompletionStage
    • thenComposeAsync

      public <U> CompletableFuture<U> thenComposeAsync(Function<? super T,​? extends CompletionStage<U>> fn, Executor executor)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that is completed with the same value as the CompletionStage returned by the given function, executed using the supplied Executor.

      When this stage completes normally, the given function is invoked with this stage's result as the argument, returning another CompletionStage. When that stage completes normally, the CompletionStage returned by this method is completed with the same value.

      To ensure progress, the supplied function must arrange eventual completion of its result.

      See the CompletionStage documentation for rules covering exceptional completion.

      Specified by:
      thenComposeAsync in interface CompletionStage<T>
      Type Parameters:
      U - the type of the returned CompletionStage's result
      Parameters:
      fn - the function to use to compute another CompletionStage
      executor - the executor to use for asynchronous execution
      Returns:
      the new CompletionStage
    • whenComplete

      public CompletableFuture<T> whenComplete(BiConsumer<? super T,​? super Throwable> action)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage with the same result or exception as this stage, that executes the given action when this stage completes.

      When this stage is complete, the given action is invoked with the result (or null if none) and the exception (or null if none) of this stage as arguments. The returned stage is completed when the action returns.

      Unlike method handle, this method is not designed to translate completion outcomes, so the supplied action should not throw an exception. However, if it does, the following rules apply: if this stage completed normally but the supplied action throws an exception, then the returned stage completes exceptionally with the supplied action's exception. Or, if this stage completed exceptionally and the supplied action throws an exception, then the returned stage completes exceptionally with this stage's exception.

      Specified by:
      whenComplete in interface CompletionStage<T>
      Parameters:
      action - the action to perform
      Returns:
      the new CompletionStage
    • whenCompleteAsync

      public CompletableFuture<T> whenCompleteAsync(BiConsumer<? super T,​? super Throwable> action)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage with the same result or exception as this stage, that executes the given action using this stage's default asynchronous execution facility when this stage completes.

      When this stage is complete, the given action is invoked with the result (or null if none) and the exception (or null if none) of this stage as arguments. The returned stage is completed when the action returns.

      Unlike method handleAsync, this method is not designed to translate completion outcomes, so the supplied action should not throw an exception. However, if it does, the following rules apply: If this stage completed normally but the supplied action throws an exception, then the returned stage completes exceptionally with the supplied action's exception. Or, if this stage completed exceptionally and the supplied action throws an exception, then the returned stage completes exceptionally with this stage's exception.

      Specified by:
      whenCompleteAsync in interface CompletionStage<T>
      Parameters:
      action - the action to perform
      Returns:
      the new CompletionStage
    • whenCompleteAsync

      public CompletableFuture<T> whenCompleteAsync(BiConsumer<? super T,​? super Throwable> action, Executor executor)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage with the same result or exception as this stage, that executes the given action using the supplied Executor when this stage completes.

      When this stage is complete, the given action is invoked with the result (or null if none) and the exception (or null if none) of this stage as arguments. The returned stage is completed when the action returns.

      Unlike method handleAsync, this method is not designed to translate completion outcomes, so the supplied action should not throw an exception. However, if it does, the following rules apply: If this stage completed normally but the supplied action throws an exception, then the returned stage completes exceptionally with the supplied action's exception. Or, if this stage completed exceptionally and the supplied action throws an exception, then the returned stage completes exceptionally with this stage's exception.

      Specified by:
      whenCompleteAsync in interface CompletionStage<T>
      Parameters:
      action - the action to perform
      executor - the executor to use for asynchronous execution
      Returns:
      the new CompletionStage
    • handle

      public <U> CompletableFuture<U> handle(BiFunction<? super T,​Throwable,​? extends U> fn)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this stage completes either normally or exceptionally, is executed with this stage's result and exception as arguments to the supplied function.

      When this stage is complete, the given function is invoked with the result (or null if none) and the exception (or null if none) of this stage as arguments, and the function's result is used to complete the returned stage.

      Specified by:
      handle in interface CompletionStage<T>
      Type Parameters:
      U - the function's return type
      Parameters:
      fn - the function to use to compute the value of the returned CompletionStage
      Returns:
      the new CompletionStage
    • handleAsync

      public <U> CompletableFuture<U> handleAsync(BiFunction<? super T,​Throwable,​? extends U> fn)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this stage completes either normally or exceptionally, is executed using this stage's default asynchronous execution facility, with this stage's result and exception as arguments to the supplied function.

      When this stage is complete, the given function is invoked with the result (or null if none) and the exception (or null if none) of this stage as arguments, and the function's result is used to complete the returned stage.

      Specified by:
      handleAsync in interface CompletionStage<T>
      Type Parameters:
      U - the function's return type
      Parameters:
      fn - the function to use to compute the value of the returned CompletionStage
      Returns:
      the new CompletionStage
    • handleAsync

      public <U> CompletableFuture<U> handleAsync(BiFunction<? super T,​Throwable,​? extends U> fn, Executor executor)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this stage completes either normally or exceptionally, is executed using the supplied executor, with this stage's result and exception as arguments to the supplied function.

      When this stage is complete, the given function is invoked with the result (or null if none) and the exception (or null if none) of this stage as arguments, and the function's result is used to complete the returned stage.

      Specified by:
      handleAsync in interface CompletionStage<T>
      Type Parameters:
      U - the function's return type
      Parameters:
      fn - the function to use to compute the value of the returned CompletionStage
      executor - the executor to use for asynchronous execution
      Returns:
      the new CompletionStage
    • toCompletableFuture

      public CompletableFuture<T> toCompletableFuture()
      Returns this CompletableFuture.
      Specified by:
      toCompletableFuture in interface CompletionStage<T>
      Returns:
      this CompletableFuture
    • exceptionally

      public CompletableFuture<T> exceptionally(Function<Throwable,​? extends T> fn)
      Description copied from interface: CompletionStage
      Returns a new CompletionStage that, when this stage completes exceptionally, is executed with this stage's exception as the argument to the supplied function. Otherwise, if this stage completes normally, then the returned stage also completes normally with the same value.
      Specified by:
      exceptionally in interface CompletionStage<T>
      Parameters:
      fn - the function to use to compute the value of the returned CompletionStage if this CompletionStage completed exceptionally
      Returns:
      the new CompletionStage
    • allOf

      public static CompletableFuture<Void> allOf(CompletableFuture<?>... cfs)
      Returns a new CompletableFuture that is completed when all of the given CompletableFutures complete. If any of the given CompletableFutures complete exceptionally, then the returned CompletableFuture also does so, with a CompletionException holding this exception as its cause. Otherwise, the results, if any, of the given CompletableFutures are not reflected in the returned CompletableFuture, but may be obtained by inspecting them individually. If no CompletableFutures are provided, returns a CompletableFuture completed with the value null.

      Among the applications of this method is to await completion of a set of independent CompletableFutures before continuing a program, as in: CompletableFuture.allOf(c1, c2, c3).join();.

      Parameters:
      cfs - the CompletableFutures
      Returns:
      a new CompletableFuture that is completed when all of the given CompletableFutures complete
      Throws:
      NullPointerException - if the array or any of its elements are null
    • anyOf

      public static CompletableFuture<Object> anyOf(CompletableFuture<?>... cfs)
      Returns a new CompletableFuture that is completed when any of the given CompletableFutures complete, with the same result. Otherwise, if it completed exceptionally, the returned CompletableFuture also does so, with a CompletionException holding this exception as its cause. If no CompletableFutures are provided, returns an incomplete CompletableFuture.
      Parameters:
      cfs - the CompletableFutures
      Returns:
      a new CompletableFuture that is completed with the result or exception of any of the given CompletableFutures when one completes
      Throws:
      NullPointerException - if the array or any of its elements are null
    • cancel

      public boolean cancel(boolean mayInterruptIfRunning)
      If not already completed, completes this CompletableFuture with a CancellationException. Dependent CompletableFutures that have not already completed will also complete exceptionally, with a CompletionException caused by this CancellationException.
      Specified by:
      cancel in interface Future<T>
      Parameters:
      mayInterruptIfRunning - this value has no effect in this implementation because interrupts are not used to control processing.
      Returns:
      true if this task is now cancelled
    • isCancelled

      public boolean isCancelled()
      Returns true if this CompletableFuture was cancelled before it completed normally.
      Specified by:
      isCancelled in interface Future<T>
      Returns:
      true if this CompletableFuture was cancelled before it completed normally
    • isCompletedNormally

      public boolean isCompletedNormally()
      Returns true if this CompletableFuture completed normally.
      Specified by:
      isCompletedNormally in interface Future<T>
      Returns:
      true if this CompletableFuture completed normally
    • isCompletedExceptionally

      public boolean isCompletedExceptionally()
      Returns true if this CompletableFuture completed exceptionally, in any way. Possible causes include cancellation, explicit invocation of completeExceptionally, and abrupt termination of a CompletionStage action.
      Returns:
      true if this CompletableFuture completed exceptionally
    • obtrudeValue

      public void obtrudeValue(T value)
      Forcibly sets or resets the value subsequently returned by method get() and related methods, whether or not already completed. This method is designed for use only in error recovery actions, and even in such situations may result in ongoing dependent completions using established versus overwritten outcomes.
      Parameters:
      value - the completion value
    • obtrudeException

      public void obtrudeException(Throwable ex)
      Forcibly causes subsequent invocations of method get() and related methods to throw the given exception, whether or not already completed. This method is designed for use only in error recovery actions, and even in such situations may result in ongoing dependent completions using established versus overwritten outcomes.
      Parameters:
      ex - the exception
      Throws:
      NullPointerException - if the exception is null
    • getNumberOfDependents

      public int getNumberOfDependents()
      Returns the estimated number of CompletableFutures whose completions are awaiting completion of this CompletableFuture. This method is designed for use in monitoring system state, not for synchronization control.
      Returns:
      the number of dependent CompletableFutures
    • toString

      public String toString()
      Returns a string identifying this CompletableFuture, as well as its completion state. The state, in brackets, contains the String "Completed Normally" or the String "Completed Exceptionally", or the String "Not completed" followed by the number of CompletableFutures dependent upon its completion, if any.
      Overrides:
      toString in class Object
      Returns:
      a string identifying this CompletableFuture, as well as its state
    • newIncompleteFuture

      public <U> CompletableFuture<U> newIncompleteFuture()
      Returns a new incomplete CompletableFuture of the type to be returned by a CompletionStage method. Subclasses should normally override this method to return an instance of the same class as this CompletableFuture. The default implementation returns an instance of class CompletableFuture.
      Type Parameters:
      U - the type of the value
      Returns:
      a new CompletableFuture
      Since:
      9
    • defaultExecutor

      public Executor defaultExecutor()
      Returns the default Executor used for async methods that do not specify an Executor. This class uses the ForkJoinPool.commonPool() if it supports more than one parallel thread, or else an Executor using one thread per async task. This method may be overridden in subclasses to return an Executor that provides at least one independent thread.
      Returns:
      the executor
      Since:
      9
    • copy

      public CompletableFuture<T> copy()
      Returns a new CompletableFuture that is completed normally with the same value as this CompletableFuture when it completes normally. If this CompletableFuture completes exceptionally, then the returned CompletableFuture completes exceptionally with a CompletionException with this exception as cause. The behavior is equivalent to thenApply(x -> x). This method may be useful as a form of "defensive copying", to prevent clients from completing, while still being able to arrange dependent actions.
      Returns:
      the new CompletableFuture
      Since:
      9
    • minimalCompletionStage

      public CompletionStage<T> minimalCompletionStage()
      Returns a new CompletionStage that is completed normally with the same value as this CompletableFuture when it completes normally, and cannot be independently completed or otherwise used in ways not defined by the methods of interface CompletionStage. If this CompletableFuture completes exceptionally, then the returned CompletionStage completes exceptionally with a CompletionException with this exception as cause.

      Unless overridden by a subclass, a new non-minimal CompletableFuture with all methods available can be obtained from a minimal CompletionStage via toCompletableFuture(). For example, completion of a minimal stage can be awaited by

       minimalStage.toCompletableFuture().join(); 
      Returns:
      the new CompletionStage
      Since:
      9
    • completeAsync

      public CompletableFuture<T> completeAsync(Supplier<? extends T> supplier, Executor executor)
      Completes this CompletableFuture with the result of the given Supplier function invoked from an asynchronous task using the given executor.
      Parameters:
      supplier - a function returning the value to be used to complete this CompletableFuture
      executor - the executor to use for asynchronous execution
      Returns:
      this CompletableFuture
      Since:
      9
    • completeAsync

      public CompletableFuture<T> completeAsync(Supplier<? extends T> supplier)
      Completes this CompletableFuture with the result of the given Supplier function invoked from an asynchronous task using the default executor.
      Parameters:
      supplier - a function returning the value to be used to complete this CompletableFuture
      Returns:
      this CompletableFuture
      Since:
      9
    • orTimeout

      public CompletableFuture<T> orTimeout(long timeout, TimeUnit unit)
      Exceptionally completes this CompletableFuture with a TimeoutException if not otherwise completed before the given timeout.
      Parameters:
      timeout - how long to wait before completing exceptionally with a TimeoutException, in units of unit
      unit - a TimeUnit determining how to interpret the timeout parameter
      Returns:
      this CompletableFuture
      Since:
      9
    • completeOnTimeout

      public CompletableFuture<T> completeOnTimeout(T value, long timeout, TimeUnit unit)
      Completes this CompletableFuture with the given value if not otherwise completed before the given timeout.
      Parameters:
      value - the value to use upon timeout
      timeout - how long to wait before completing normally with the given value, in units of unit
      unit - a TimeUnit determining how to interpret the timeout parameter
      Returns:
      this CompletableFuture
      Since:
      9
    • delayedExecutor

      public static Executor delayedExecutor(long delay, TimeUnit unit, Executor executor)
      Returns a new Executor that submits a task to the given base executor after the given delay (or no delay if non-positive). Each delay commences upon invocation of the returned executor's execute method.
      Parameters:
      delay - how long to delay, in units of unit
      unit - a TimeUnit determining how to interpret the delay parameter
      executor - the base executor
      Returns:
      the new delayed executor
      Since:
      9
    • delayedExecutor

      public static Executor delayedExecutor(long delay, TimeUnit unit)
      Returns a new Executor that submits a task to the default executor after the given delay (or no delay if non-positive). Each delay commences upon invocation of the returned executor's execute method.
      Parameters:
      delay - how long to delay, in units of unit
      unit - a TimeUnit determining how to interpret the delay parameter
      Returns:
      the new delayed executor
      Since:
      9
    • completedStage

      public static <U> CompletionStage<U> completedStage(U value)
      Returns a new CompletionStage that is already completed with the given value and supports only those methods in interface CompletionStage.
      Type Parameters:
      U - the type of the value
      Parameters:
      value - the value
      Returns:
      the completed CompletionStage
      Since:
      9
    • failedFuture

      public static <U> CompletableFuture<U> failedFuture(Throwable ex)
      Returns a new CompletableFuture that is already completed exceptionally with the given exception.
      Type Parameters:
      U - the type of the value
      Parameters:
      ex - the exception
      Returns:
      the exceptionally completed CompletableFuture
      Since:
      9
    • failedStage

      public static <U> CompletionStage<U> failedStage(Throwable ex)
      Returns a new CompletionStage that is already completed exceptionally with the given exception and supports only those methods in interface CompletionStage.
      Type Parameters:
      U - the type of the value
      Parameters:
      ex - the exception
      Returns:
      the exceptionally completed CompletionStage
      Since:
      9
    • completed

      public static <T> Stream<CompletableFuture<T>> completed(Collection<? extends CompletableFuture<T>> cfs)
      Returns a stream that is lazily populated with the given CompletableFutures when they complete.

      If a thread is interrupted while waiting on the stream for a task to complete then CancellationException is thrown with the interrupt status set.

      API Note:
      The following example has a list of CompletableFuture objects. It selects the result of the first to complete and then cancels the remaining (that have not completed).
       
           List<CompletableFuture<String>> cfs = ...
           try {
               String first = CompletableFuture.completed(cfs)
                           .filter(Predicate.not(CompletableFuture::isCompletedExceptionally))
                           .map(CompletableFuture::join)
                           .findFirst()
                           .orElse(null);
           } finally {
               cfs.forEach(cf -> cf.cancel(true));
           }
       

      The following example partitions the CompletableFutures into two sets, one for the tasks that completed successfully, the other for the tasks that completed with an exception.

      
           List<CompletableFuture<String>> cfs = ...
           Map<Boolean, Set<CompletableFuture<String>>> map = CompletableFuture.completed(cfs)
                   .collect(Collectors.partitioningBy(CompletableFuture::isCompletedExceptionally,
                                                      Collectors.toSet()));
       
      Type Parameters:
      T - the result type returned by completable future's join
      Parameters:
      cfs - the CompletableFutures
      Returns:
      stream of completed CompletableFutures
      Throws:
      NullPointerException - if the collection or any of its elements are null
      Since:
      99
    • completed

      @SafeVarargs public static <T> Stream<CompletableFuture<T>> completed(CompletableFuture<T>... cfs)
      Returns a stream that is lazily populated with the given CompletableFutures when they complete.

      If a thread is interrupted while waiting on the stream for a task to complete then CancellationException is thrown with the interrupt status set.

      Type Parameters:
      T - the result type returned by completable future's join
      Parameters:
      cfs - the CompletableFutures
      Returns:
      stream of completed CompletableFutures
      Throws:
      NullPointerException - if the array or any of its elements are null
      Since:
      99