- java.lang.Object
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- java.util.concurrent.CompletableFuture<T>
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- Type Parameters:
T
- The result type returned by this future'sjoin
andget
methods
- All Implemented Interfaces:
CompletionStage<T>
,Future<T>
public class CompletableFuture<T> extends Object implements Future<T>, CompletionStage<T>
AFuture
that may be explicitly completed (setting its value and status), and may be used as aCompletionStage
, supporting dependent functions and actions that trigger upon its completion.When two or more threads attempt to
complete
,completeExceptionally
, orcancel
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 methoddefaultExecutor()
. To simplify monitoring, debugging, and tracking, all generated asynchronous tasks are instances of the marker interfaceCompletableFuture.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 methodcopy()
.
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. Methodcancel
has the same effect ascompleteExceptionally(new CancellationException())
. MethodisCompletedExceptionally()
can be used to determine if a CompletableFuture completed in any exceptional fashion. - In case of exceptional completion with a CompletionException,
methods
get()
andget(long, TimeUnit)
throw anExecutionException
with the same cause as held in the corresponding CompletionException. To simplify usage in most contexts, this class also defines methodsjoin()
andgetNow(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 aNullPointerException
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 theobtrude
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
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Nested Class Summary
Nested Classes Modifier and Type Class Description static interface
CompletableFuture.AsynchronousCompletionTask
A marker interface identifying asynchronous tasks produced byasync
methods.
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Constructor Summary
Constructors Constructor Description CompletableFuture()
Creates a new incomplete CompletableFuture.
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description 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.boolean
cancel(boolean mayInterruptIfRunning)
If not already completed, completes this CompletableFuture with aCancellationException
.boolean
complete(T value)
If not already completed, sets the value returned byget()
and related methods to the given value.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.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.static <U> CompletableFuture<U>
completedFuture(U value)
Returns a new CompletableFuture that is already completed with the given value.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 interfaceCompletionStage
.boolean
completeExceptionally(Throwable ex)
If not already completed, causes invocations ofget()
and related methods to throw the given exception.CompletableFuture<T>
completeOnTimeout(T value, long timeout, TimeUnit unit)
Completes this CompletableFuture with the given value if not otherwise completed before the given timeout.CompletableFuture<T>
copy()
Returns a new CompletableFuture that is completed normally with the same value as this CompletableFuture when it completes normally.Executor
defaultExecutor()
Returns the default Executor used for async methods that do not specify an Executor.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).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).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.static <U> CompletableFuture<U>
failedFuture(Throwable ex)
Returns a new CompletableFuture that is already completed exceptionally with the given exception.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 interfaceCompletionStage
.T
get()
Waits if necessary for this future to complete, and then returns its result.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
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.boolean
isCancelled()
Returnstrue
if this CompletableFuture was cancelled before it completed normally.boolean
isCompletedExceptionally()
Returnstrue
if this CompletableFuture completed exceptionally, in any way.boolean
isDone()
Returnstrue
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.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 interfaceCompletionStage
.<U> CompletableFuture<U>
newIncompleteFuture()
Returns a new incomplete CompletableFuture of the type to be returned by a CompletionStage method.void
obtrudeException(Throwable ex)
Forcibly causes subsequent invocations of methodget()
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 methodget()
and related methods, whether or not already completed.CompletableFuture<T>
orTimeout(long timeout, TimeUnit unit)
Exceptionally completes this CompletableFuture with aTimeoutException
if not otherwise completed before the given timeout.static CompletableFuture<Void>
runAsync(Runnable runnable)
Returns a new CompletableFuture that is asynchronously completed by a task running in theForkJoinPool.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 theForkJoinPool.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<T>
toCompletableFuture()
Returns this CompletableFuture.String
toString()
Returns a string identifying this CompletableFuture, as well as its completion state.-
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
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Methods declared in interface java.util.concurrent.CompletionStage
acceptEither, acceptEitherAsync, acceptEitherAsync, applyToEither, applyToEitherAsync, applyToEitherAsync, handle, handleAsync, handleAsync, runAfterBoth, runAfterBothAsync, runAfterBothAsync, runAfterEither, runAfterEitherAsync, runAfterEitherAsync, thenAccept, thenAcceptAsync, thenAcceptAsync, thenAcceptBoth, thenAcceptBothAsync, thenAcceptBothAsync, thenApply, thenApplyAsync, thenApplyAsync, thenCombine, thenCombineAsync, thenCombineAsync, thenCompose, thenComposeAsync, thenComposeAsync, thenRun, thenRunAsync, thenRunAsync, whenComplete, whenCompleteAsync, whenCompleteAsync
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Method Detail
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supplyAsync
public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier)
Returns a new CompletableFuture that is asynchronously completed by a task running in theForkJoinPool.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
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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 CompletableFutureexecutor
- the executor to use for asynchronous execution- Returns:
- the new CompletableFuture
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runAsync
public static CompletableFuture<Void> runAsync(Runnable runnable)
Returns a new CompletableFuture that is asynchronously completed by a task running in theForkJoinPool.commonPool()
after it runs the given action.- Parameters:
runnable
- the action to run before completing the returned CompletableFuture- Returns:
- the new CompletableFuture
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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 CompletableFutureexecutor
- the executor to use for asynchronous execution- Returns:
- the new CompletableFuture
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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
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isDone
public boolean isDone()
Returnstrue
if completed in any fashion: normally, exceptionally, or via cancellation.
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get
public T get() throws InterruptedException, ExecutionException
Waits if necessary for this future to complete, and then returns its result.- Specified by:
get
in interfaceFuture<T>
- Returns:
- the result value
- Throws:
CancellationException
- if this future was cancelledExecutionException
- if this future completed exceptionallyInterruptedException
- if the current thread was interrupted while waiting
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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 interfaceFuture<T>
- Parameters:
timeout
- the maximum time to waitunit
- the time unit of the timeout argument- Returns:
- the result value
- Throws:
CancellationException
- if this future was cancelledExecutionException
- if this future completed exceptionallyInterruptedException
- if the current thread was interrupted while waitingTimeoutException
- if the wait timed out
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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.- Returns:
- the result value
- Throws:
CancellationException
- if the computation was cancelledCompletionException
- if this future completed exceptionally or a completion computation threw an exception
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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 cancelledCompletionException
- if this future completed exceptionally or a completion computation threw an exception
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complete
public boolean complete(T value)
If not already completed, sets the value returned byget()
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, elsefalse
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completeExceptionally
public boolean completeExceptionally(Throwable ex)
If not already completed, causes invocations ofget()
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, elsefalse
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toCompletableFuture
public CompletableFuture<T> toCompletableFuture()
Returns this CompletableFuture.- Specified by:
toCompletableFuture
in interfaceCompletionStage<T>
- Returns:
- this CompletableFuture
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exceptionally
public 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. Note: More flexible versions of this functionality are available using methodswhenComplete
andhandle
.- Specified by:
exceptionally
in interfaceCompletionStage<T>
- Parameters:
fn
- the function to use to compute the value of the returned CompletableFuture if this CompletableFuture completed exceptionally- Returns:
- the new CompletableFuture
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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 valuenull
.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 arenull
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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 arenull
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cancel
public boolean cancel(boolean mayInterruptIfRunning)
If not already completed, completes this CompletableFuture with aCancellationException
. Dependent CompletableFutures that have not already completed will also complete exceptionally, with aCompletionException
caused by thisCancellationException
.
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isCancelled
public boolean isCancelled()
Returnstrue
if this CompletableFuture was cancelled before it completed normally.- Specified by:
isCancelled
in interfaceFuture<T>
- Returns:
true
if this CompletableFuture was cancelled before it completed normally
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isCompletedExceptionally
public boolean isCompletedExceptionally()
Returnstrue
if this CompletableFuture completed exceptionally, in any way. Possible causes include cancellation, explicit invocation ofcompleteExceptionally
, and abrupt termination of a CompletionStage action.- Returns:
true
if this CompletableFuture completed exceptionally
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obtrudeValue
public void obtrudeValue(T value)
Forcibly sets or resets the value subsequently returned by methodget()
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
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obtrudeException
public void obtrudeException(Throwable ex)
Forcibly causes subsequent invocations of methodget()
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
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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
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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.
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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
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defaultExecutor
public Executor defaultExecutor()
Returns the default Executor used for async methods that do not specify an Executor. This class uses theForkJoinPool.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
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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 tothenApply(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
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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 interfaceCompletionStage
. 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 byminimalStage.toCompletableFuture().join();
- Returns:
- the new CompletionStage
- Since:
- 9
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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 CompletableFutureexecutor
- the executor to use for asynchronous execution- Returns:
- this CompletableFuture
- Since:
- 9
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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
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orTimeout
public CompletableFuture<T> orTimeout(long timeout, TimeUnit unit)
Exceptionally completes this CompletableFuture with aTimeoutException
if not otherwise completed before the given timeout.- Parameters:
timeout
- how long to wait before completing exceptionally with a TimeoutException, in units ofunit
unit
- aTimeUnit
determining how to interpret thetimeout
parameter- Returns:
- this CompletableFuture
- Since:
- 9
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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 timeouttimeout
- how long to wait before completing normally with the given value, in units ofunit
unit
- aTimeUnit
determining how to interpret thetimeout
parameter- Returns:
- this CompletableFuture
- Since:
- 9
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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'sexecute
method.- Parameters:
delay
- how long to delay, in units ofunit
unit
- aTimeUnit
determining how to interpret thedelay
parameterexecutor
- the base executor- Returns:
- the new delayed executor
- Since:
- 9
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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'sexecute
method.- Parameters:
delay
- how long to delay, in units ofunit
unit
- aTimeUnit
determining how to interpret thedelay
parameter- Returns:
- the new delayed executor
- Since:
- 9
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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 interfaceCompletionStage
.- Type Parameters:
U
- the type of the value- Parameters:
value
- the value- Returns:
- the completed CompletionStage
- Since:
- 9
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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
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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 interfaceCompletionStage
.- Type Parameters:
U
- the type of the value- Parameters:
ex
- the exception- Returns:
- the exceptionally completed CompletionStage
- Since:
- 9
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