Class CompletableFuture<T>
- java.lang.Object
-
- java.util.concurrent.CompletableFuture<T>
- 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>
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 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 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
Nested Class Summary
Modifier and Type | Class | Description |
---|---|---|
static interface | CompletableFuture.AsynchronousCompletionTask | A marker interface identifying asynchronous tasks produced by |
Constructor Summary
Constructor | Description |
---|---|
CompletableFuture() | Creates a new incomplete CompletableFuture. |
Method Summary
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 a |
boolean | complete(T value) | If not already completed, sets the value returned by |
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 interface |
boolean | completeExceptionally(Throwable ex) | If not already completed, causes invocations of |
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 interface |
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() | Returns |
boolean | isCompletedExceptionally() | Returns |
boolean | isDone() | Returns |
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 interface |
<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 method |
void | obtrudeValue(T value) | Forcibly sets or resets the value subsequently returned by method |
CompletableFuture<T> | orTimeout(long timeout,
TimeUnit unit) | Exceptionally completes this CompletableFuture with a |
static CompletableFuture<Void> | runAsync(Runnable runnable) | Returns a new CompletableFuture that is asynchronously completed by a task running in the |
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 |
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
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
Constructor Detail
CompletableFuture
public CompletableFuture()
Creates a new incomplete CompletableFuture.
Method Detail
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.
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 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 interfaceFuture<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.
- 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, elsefalse
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, elsefalse
toCompletableFuture
public CompletableFuture<T> toCompletableFuture()
Returns this CompletableFuture.
- Specified by:
-
toCompletableFuture
in interfaceCompletionStage<T>
- Returns:
- this CompletableFuture
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 methods whenComplete
and handle
.
- 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
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 arenull
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
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 interfaceFuture<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 interfaceFuture<T>
- Returns:
-
true
if this CompletableFuture was cancelled before it 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 classObject
- 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 ofunit
-
unit
- aTimeUnit
determining how to interpret thetimeout
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 ofunit
-
unit
- aTimeUnit
determining how to interpret thetimeout
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 ofunit
-
unit
- aTimeUnit
determining how to interpret thedelay
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 ofunit
-
unit
- aTimeUnit
determining how to interpret thedelay
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