CompletableFuture

public class CompletableFuture 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). 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.

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.

Nested Class Summary

interface CompletableFuture.AsynchronousCompletionTask A marker interface identifying asynchronous tasks produced by async methods. 

Public Constructor Summary

CompletableFuture()
Creates a new incomplete CompletableFuture.

Public Method Summary

CompletableFuture<Void>
acceptEither(CompletionStage<? extends T> other, Consumer<? super T> action)
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.
CompletableFuture<Void>
acceptEitherAsync(CompletionStage<? extends T> other, Consumer<? super T> action)
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.
CompletableFuture<Void>
acceptEitherAsync(CompletionStage<? extends T> other, Consumer<? super T> action, Executor executor)
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.
static CompletableFuture<Void>
allOf(CompletableFuture...<?> cfs)
Returns a new CompletableFuture that is completed when all of the given CompletableFutures complete.
static CompletableFuture<Object>
anyOf(CompletableFuture...<?> cfs)
Returns a new CompletableFuture that is completed when any of the given CompletableFutures complete, with the same result.
<U> CompletableFuture<U>
applyToEither(CompletionStage<? extends T> other, Function<? super T, U> fn)
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.
<U> CompletableFuture<U>
applyToEitherAsync(CompletionStage<? extends T> other, Function<? super T, U> fn)
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.
<U> CompletableFuture<U>
applyToEitherAsync(CompletionStage<? extends T> other, Function<? super T, U> fn, Executor executor)
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.
boolean
cancel(boolean mayInterruptIfRunning)
If not already completed, completes this CompletableFuture with a CancellationException.
boolean
complete(T value)
If not already completed, sets the value returned by get() and related methods to the given value.
boolean
completeExceptionally(Throwable ex)
If not already completed, causes invocations of get() and related methods to throw the given exception.
static <U> CompletableFuture<U>
completedFuture(U value)
Returns a new CompletableFuture that is already completed with the given value.
CompletableFuture<T>
exceptionally(Function<Throwable, ? extends T> fn)
Returns a new CompletableFuture that is completed when this CompletableFuture completes, with the result of the given function of the exception triggering this CompletableFuture's completion when it completes exceptionally; otherwise, if this CompletableFuture completes normally, then the returned CompletableFuture also completes normally with the same value.
T
get(long timeout, TimeUnit unit)
Waits if necessary for at most the given time for this future to complete, and then returns its result, if available.
T
get()
Waits if necessary for this future to complete, and then returns its result.
T
getNow(T valueIfAbsent)
Returns the result value (or throws any encountered exception) if completed, else returns the given valueIfAbsent.
int
getNumberOfDependents()
Returns the estimated number of CompletableFutures whose completions are awaiting completion of this CompletableFuture.
<U> CompletableFuture<U>
handle(BiFunction<? super T, Throwable, ? extends U> fn)
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.
<U> CompletableFuture<U>
handleAsync(BiFunction<? super T, Throwable, ? extends U> fn, Executor executor)
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.
<U> CompletableFuture<U>
handleAsync(BiFunction<? super T, Throwable, ? extends U> fn)
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.
boolean
isCancelled()
Returns true if this CompletableFuture was cancelled before it completed normally.
boolean
isCompletedExceptionally()
Returns true if this CompletableFuture completed exceptionally, in any way.
boolean
isDone()
Returns true if completed in any fashion: normally, exceptionally, or via cancellation.
T
join()
Returns the result value when complete, or throws an (unchecked) exception if completed exceptionally.
void
obtrudeException(Throwable ex)
Forcibly causes subsequent invocations of method get() and related methods to throw the given exception, whether or not already completed.
void
obtrudeValue(T value)
Forcibly sets or resets the value subsequently returned by method get() and related methods, whether or not already completed.
CompletableFuture<Void>
runAfterBoth(CompletionStage<?> other, Runnable action)
Returns a new CompletionStage that, when this and the other given stage both complete normally, executes the given action.
CompletableFuture<Void>
runAfterBothAsync(CompletionStage<?> other, Runnable action)
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.
CompletableFuture<Void>
runAfterBothAsync(CompletionStage<?> other, Runnable action, Executor executor)
Returns a new CompletionStage that, when this and the other given stage both complete normally, executes the given action using the supplied executor.
CompletableFuture<Void>
runAfterEither(CompletionStage<?> other, Runnable action)
Returns a new CompletionStage that, when either this or the other given stage complete normally, executes the given action.
CompletableFuture<Void>
runAfterEitherAsync(CompletionStage<?> other, Runnable action, Executor executor)
Returns a new CompletionStage that, when either this or the other given stage complete normally, executes the given action using the supplied executor.
CompletableFuture<Void>
runAfterEitherAsync(CompletionStage<?> other, Runnable action)
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.
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.
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.
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.
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.
CompletableFuture<Void>
thenAccept(Consumer<? super T> action)
Returns a new CompletionStage that, when this stage completes normally, is executed with this stage's result as the argument to the supplied action.
CompletableFuture<Void>
thenAcceptAsync(Consumer<? super T> action, Executor executor)
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.
CompletableFuture<Void>
thenAcceptAsync(Consumer<? super T> action)
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.
<U> CompletableFuture<Void>
thenAcceptBoth(CompletionStage<? extends U> other, BiConsumer<? super T, ? super U> action)
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.
<U> CompletableFuture<Void>
thenAcceptBothAsync(CompletionStage<? extends U> other, BiConsumer<? super T, ? super U> action, Executor executor)
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.
<U> CompletableFuture<Void>
thenAcceptBothAsync(CompletionStage<? extends U> other, BiConsumer<? super T, ? super U> action)
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.
<U> CompletableFuture<U>
thenApply(Function<? super T, ? extends U> fn)
Returns a new CompletionStage that, when this stage completes normally, is executed with this stage's result as the argument to the supplied function.
<U> CompletableFuture<U>
thenApplyAsync(Function<? super T, ? extends U> fn)
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.
<U> CompletableFuture<U>
thenApplyAsync(Function<? super T, ? extends U> fn, Executor executor)
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.
<U, V> CompletableFuture<V>
thenCombine(CompletionStage<? extends U> other, BiFunction<? super T, ? super U, ? extends V> fn)
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.
<U, V> CompletableFuture<V>
thenCombineAsync(CompletionStage<? extends U> other, BiFunction<? super T, ? super U, ? extends V> fn, Executor executor)
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.
<U, V> CompletableFuture<V>
thenCombineAsync(CompletionStage<? extends U> other, BiFunction<? super T, ? super U, ? extends V> fn)
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.
<U> CompletableFuture<U>
thenCompose(Function<? super T, ? extends CompletionStage<U>> fn)
Returns a new CompletionStage that is completed with the same value as the CompletionStage returned by the given function.
<U> CompletableFuture<U>
thenComposeAsync(Function<? super T, ? extends CompletionStage<U>> fn, Executor executor)
Returns a new CompletionStage that is completed with the same value as the CompletionStage returned by the given function, executed using the supplied Executor.
<U> CompletableFuture<U>
thenComposeAsync(Function<? super T, ? extends CompletionStage<U>> fn)
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.
CompletableFuture<Void>
thenRun(Runnable action)
Returns a new CompletionStage that, when this stage completes normally, executes the given action.
CompletableFuture<Void>
thenRunAsync(Runnable action, Executor executor)
Returns a new CompletionStage that, when this stage completes normally, executes the given action using the supplied Executor.
CompletableFuture<Void>
thenRunAsync(Runnable action)
Returns a new CompletionStage that, when this stage completes normally, executes the given action using this stage's default asynchronous execution facility.
CompletableFuture<T>
toCompletableFuture()
Returns this CompletableFuture.
String
toString()
Returns a string identifying this CompletableFuture, as well as its completion state.
CompletableFuture<T>
whenComplete(BiConsumer<? super T, ? super Throwable> action)
Returns a new CompletionStage with the same result or exception as this stage, that executes the given action when this stage completes.
CompletableFuture<T>
whenCompleteAsync(BiConsumer<? super T, ? super Throwable> action)
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.
CompletableFuture<T>
whenCompleteAsync(BiConsumer<? super T, ? super Throwable> action, Executor executor)
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.

Inherited Method Summary

Public Constructors

public CompletableFuture ()

Creates a new incomplete CompletableFuture.

Public Methods

public CompletableFuture<Void> acceptEither (CompletionStage<? extends T> other, Consumer<? super T> action)

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.

Parameters
other the other CompletionStage
action the action to perform before completing the returned CompletionStage
Returns
  • the new CompletionStage

public CompletableFuture<Void> acceptEitherAsync (CompletionStage<? extends T> other, Consumer<? super T> action)

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.

Parameters
other the other CompletionStage
action the action to perform before completing the returned CompletionStage
Returns
  • the new CompletionStage

public CompletableFuture<Void> acceptEitherAsync (CompletionStage<? extends T> other, Consumer<? super T> action, Executor executor)

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.

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

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

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

public CompletableFuture<U> applyToEither (CompletionStage<? extends T> other, Function<? super T, U> fn)

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.

Parameters
other the other CompletionStage
fn the function to use to compute the value of the returned CompletionStage
Returns
  • the new CompletionStage

public CompletableFuture<U> applyToEitherAsync (CompletionStage<? extends T> other, Function<? super T, U> fn)

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.

Parameters
other the other CompletionStage
fn the function to use to compute the value of the returned CompletionStage
Returns
  • the new CompletionStage

public CompletableFuture<U> applyToEitherAsync (CompletionStage<? extends T> other, Function<? super T, U> fn, Executor executor)

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.

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

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.

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

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

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

public static CompletableFuture<U> completedFuture (U value)

Returns a new CompletableFuture that is already completed with the given value.

Parameters
value the value
Returns
  • the completed CompletableFuture

public