T
- the type of values the stage produces or consumesCompletableFuture
public interface CompletionStage<T>
stage.thenApply(x -> square(x))
.thenAccept(x -> System.out.print(x))
.thenRun(() -> System.out.println());
An additional form (compose) allows the construction of computation pipelines from functions returning completion stages. Any argument to a stage's computation is the outcome of a triggering stage's computation.
Executor
). The execution properties of default and async modes are specified by CompletionStage implementations, not this interface. Methods with explicit Executor arguments may have arbitrary execution properties, and might not even support concurrent execution, but are arranged for processing in a way that accommodates asynchrony. handle
and whenComplete
) support unconditional computation whether the triggering stage completed normally or exceptionally. Method exceptionally
supports computation only when the triggering stage completes exceptionally, computing a replacement result, similarly to the java catch
keyword. In all other cases, if a stage's computation terminates abruptly with an (unchecked) exception or error, then all dependent stages requiring its completion complete exceptionally as well, with a CompletionException
holding the exception as its cause. If a stage is dependent on both of two stages, and both complete exceptionally, then the CompletionException may correspond to either one of these exceptions. If a stage is dependent on either of two others, and only one of them completes exceptionally, no guarantees are made about whether the dependent stage completes normally or exceptionally. In the case of method whenComplete
, when the supplied action itself encounters an exception, then the stage completes exceptionally with this exception unless the source stage also completed exceptionally, in which case the exceptional completion from the source stage is given preference and propagated to the dependent stage. All methods adhere to the above triggering, execution, and exceptional completion specifications (which are not repeated in individual method specifications). Additionally, while arguments used to pass a completion result (that is, for parameters of type T
) for methods accepting them may be null, passing a null value for any other parameter will result in a NullPointerException
being thrown.
Method form handle
is the most general way of creating a continuation stage, unconditionally performing a computation that is given both the result and exception (if any) of the triggering CompletionStage, and computing an arbitrary result. Method whenComplete
is similar, but preserves the result of the triggering stage instead of computing a new one. Because a stage's normal result may be null
, both methods should have a computation structured thus:
(result, exception) -> {
if (exception == null) {
// triggering stage completed normally
} else {
// triggering stage completed exceptionally
}
}
This interface does not define methods for initially creating, forcibly completing normally or exceptionally, probing completion status or results, or awaiting completion of a stage. Implementations of CompletionStage may provide means of achieving such effects, as appropriate. Method toCompletableFuture()
enables interoperability among different implementations of this interface by providing a common conversion type.
Modifier and Type | Method | Description |
---|---|---|
CompletionStage |
acceptEither |
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. |
CompletionStage |
acceptEitherAsync |
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. |
CompletionStage |
acceptEitherAsync |
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. |
<U> CompletionStage |
applyToEither |
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> CompletionStage |
applyToEitherAsync |
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> CompletionStage |
applyToEitherAsync |
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. |
CompletionStage |
exceptionally |
Returns a new CompletionStage that, when this stage completes exceptionally, is executed with this stage's exception as the argument to the supplied function. |
default CompletionStage |
exceptionallyAsync |
Returns a new CompletionStage that, when this stage completes exceptionally, is executed with this stage's exception as the argument to the supplied function, using this stage's default asynchronous execution facility. |
default CompletionStage |
exceptionallyAsync |
Returns a new CompletionStage that, when this stage completes exceptionally, is executed with this stage's exception as the argument to the supplied function, using the supplied Executor. |
default CompletionStage |
exceptionallyCompose |
Returns a new CompletionStage that, when this stage completes exceptionally, is composed using the results of the supplied function applied to this stage's exception. |
default CompletionStage |
exceptionallyComposeAsync |
Returns a new CompletionStage that, when this stage completes exceptionally, is composed using the results of the supplied function applied to this stage's exception, using this stage's default asynchronous execution facility. |
default CompletionStage |
exceptionallyComposeAsync |
Returns a new CompletionStage that, when this stage completes exceptionally, is composed using the results of the supplied function applied to this stage's exception, using the supplied Executor. |
<U> CompletionStage |
handle |
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> CompletionStage |
handleAsync |
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. |
<U> CompletionStage |
handleAsync |
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. |
CompletionStage |
runAfterBoth |
Returns a new CompletionStage that, when this and the other given stage both complete normally, executes the given action. |
CompletionStage |
runAfterBothAsync |
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. |
CompletionStage |
runAfterBothAsync |
Returns a new CompletionStage that, when this and the other given stage both complete normally, executes the given action using the supplied executor. |
CompletionStage |
runAfterEither |
Returns a new CompletionStage that, when either this or the other given stage complete normally, executes the given action. |
CompletionStage |
runAfterEitherAsync |
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. |
CompletionStage |
runAfterEitherAsync |
Returns a new CompletionStage that, when either this or the other given stage complete normally, executes the given action using the supplied executor. |
CompletionStage |
thenAccept |
Returns a new CompletionStage that, when this stage completes normally, is executed with this stage's result as the argument to the supplied action. |
CompletionStage |
thenAcceptAsync |
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. |
CompletionStage |
thenAcceptAsync |
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. |
<U> CompletionStage |
thenAcceptBoth |
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> CompletionStage |
thenAcceptBothAsync |
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> CompletionStage |
thenAcceptBothAsync |
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> CompletionStage |
thenApply |
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> CompletionStage |
thenApplyAsync |
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> CompletionStage |
thenApplyAsync |
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, |
thenCombine |
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, |
thenCombineAsync |
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, |
thenCombineAsync |
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> CompletionStage |
thenCompose |
Returns a new CompletionStage that is completed with the same value as the CompletionStage returned by the given function. |
<U> CompletionStage |
thenComposeAsync |
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. |
<U> CompletionStage |
thenComposeAsync |
Returns a new CompletionStage that is completed with the same value as the CompletionStage returned by the given function, executed using the supplied Executor. |
CompletionStage |
thenRun |
Returns a new CompletionStage that, when this stage completes normally, executes the given action. |
CompletionStage |
thenRunAsync |
Returns a new CompletionStage that, when this stage completes normally, executes the given action using this stage's default asynchronous execution facility. |
CompletionStage |
thenRunAsync |
Returns a new CompletionStage that, when this stage completes normally, executes the given action using the supplied Executor. |
CompletableFuture |
toCompletableFuture() |
Returns a CompletableFuture maintaining the same completion properties as this stage. |
CompletionStage |
whenComplete |
Returns a new CompletionStage with the same result or exception as this stage, that executes the given action when this stage completes. |
CompletionStage |
whenCompleteAsync |
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. |
CompletionStage |
whenCompleteAsync |
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. |
<U> CompletionStage<U> thenApply(Function<? super T,? extends U> fn)
This method is analogous to Optional.map
and Stream.map
.
See the CompletionStage
documentation for rules covering exceptional completion.
U
- the function's return typefn
- the function to use to compute the value of the returned CompletionStage<U> CompletionStage<U> thenApplyAsync(Function<? super T,? extends U> fn)
CompletionStage
documentation for rules covering exceptional completion.U
- the function's return typefn
- the function to use to compute the value of the returned CompletionStage<U> CompletionStage<U> thenApplyAsync(Function<? super T,? extends U> fn, Executor executor)
CompletionStage
documentation for rules covering exceptional completion.U
- the function's return typefn
- the function to use to compute the value of the returned CompletionStageexecutor
- the executor to use for asynchronous executionCompletionStage<Void> thenAccept(Consumer<? super T> action)
CompletionStage
documentation for rules covering exceptional completion.action
- the action to perform before completing the returned CompletionStageCompletionStage<Void> thenAcceptAsync(Consumer<? super T> action)
CompletionStage
documentation for rules covering exceptional completion.action
- the action to perform before completing the returned CompletionStageCompletionStage<Void> thenAcceptAsync(Consumer<? super T> action, Executor executor)
CompletionStage
documentation for rules covering exceptional completion.action
- the action to perform before completing the returned CompletionStageexecutor
- the executor to use for asynchronous executionCompletionStage<Void> thenRun(Runnable action)
CompletionStage
documentation for rules covering exceptional completion.action
- the action to perform before completing the returned CompletionStageCompletionStage<Void> thenRunAsync(Runnable action)
CompletionStage
documentation for rules covering exceptional completion.action
- the action to perform before completing the returned CompletionStageCompletionStage<Void> thenRunAsync(Runnable action, Executor executor)
CompletionStage
documentation for rules covering exceptional completion.action
- the action to perform before completing the returned CompletionStageexecutor
- the executor to use for asynchronous execution<U, V> CompletionStage<V> thenCombine(CompletionStage<? extends U> other, BiFunction<? super T,? super U,? extends V> fn)
CompletionStage
documentation for rules covering exceptional completion.U
- the type of the other CompletionStage's resultV
- the function's return typeother
- the other CompletionStagefn
- the function to use to compute the value of the returned CompletionStage<U, V> CompletionStage<V> thenCombineAsync(CompletionStage<? extends U> other, BiFunction<? super T,? super U,? extends V> fn)
CompletionStage
documentation for rules covering exceptional completion.U
- the type of the other CompletionStage's resultV
- the function's return typeother
- the other CompletionStagefn
- the function to use to compute the value of the returned CompletionStage<U, V> CompletionStage<V> thenCombineAsync(CompletionStage<? extends U> other, BiFunction<? super T,? super U,? extends V> fn, Executor executor)
CompletionStage
documentation for rules covering exceptional completion.U
- the type of the other CompletionStage's resultV
- the function's return typeother
- the other CompletionStagefn
- the function to use to compute the value of the returned CompletionStageexecutor
- the executor to use for asynchronous execution<U> CompletionStage<Void> thenAcceptBoth(CompletionStage<? extends U> other, BiConsumer<? super T,? super U> action)
CompletionStage
documentation for rules covering exceptional completion.U
- the type of the other CompletionStage's resultother
- the other CompletionStageaction
- the action to perform before completing the returned CompletionStage<U> CompletionStage<Void> thenAcceptBothAsync(CompletionStage<? extends U> other, BiConsumer<? super T,? super U> action)
CompletionStage
documentation for rules covering exceptional completion.U
- the type of the other CompletionStage's resultother
- the other CompletionStageaction
- the action to perform before completing the returned CompletionStage<U> CompletionStage<Void> thenAcceptBothAsync(CompletionStage<? extends U> other, BiConsumer<? super T,? super U> action, Executor executor)
CompletionStage
documentation for rules covering exceptional completion.U
- the type of the other CompletionStage's resultother
- the other CompletionStageaction
- the action to perform before completing the returned CompletionStageexecutor
- the executor to use for asynchronous executionCompletionStage<Void> runAfterBoth(CompletionStage<?> other, Runnable action)
CompletionStage
documentation for rules covering exceptional completion.other
- the other CompletionStageaction
- the action to perform before completing the returned CompletionStageCompletionStage<Void> runAfterBothAsync(CompletionStage<?> other, Runnable action)
CompletionStage
documentation for rules covering exceptional completion.other
- the other CompletionStageaction
- the action to perform before completing the returned CompletionStageCompletionStage<Void> runAfterBothAsync(CompletionStage<?> other, Runnable action, Executor executor)
CompletionStage
documentation for rules covering exceptional completion.other
- the other CompletionStageaction
- the action to perform before completing the returned CompletionStageexecutor
- the executor to use for asynchronous execution<U> CompletionStage<U> applyToEither(CompletionStage<? extends T> other, Function<? super T,U> fn)
CompletionStage
documentation for rules covering exceptional completion.U
- the function's return typeother
- the other CompletionStagefn
- the function to use to compute the value of the returned CompletionStage<U> CompletionStage<U> applyToEitherAsync(CompletionStage<? extends T> other, Function<? super T,U> fn)
CompletionStage
documentation for rules covering exceptional completion.U
- the function's return typeother
- the other CompletionStagefn
- the function to use to compute the value of the returned CompletionStage<U> CompletionStage<U> applyToEitherAsync(CompletionStage<? extends T> other, Function<? super T,U> fn, Executor executor)
CompletionStage
documentation for rules covering exceptional completion.U
- the function's return typeother
- the other CompletionStagefn
- the function to use to compute the value of the returned CompletionStageexecutor
- the executor to use for asynchronous executionCompletionStage<Void> acceptEither(CompletionStage<? extends T> other, Consumer<? super T> action)
CompletionStage
documentation for rules covering exceptional completion.other
- the other CompletionStageaction
- the action to perform before completing the returned CompletionStageCompletionStage<Void> acceptEitherAsync(CompletionStage<? extends T> other, Consumer<? super T> action)
CompletionStage
documentation for rules covering exceptional completion.other
- the other CompletionStageaction
- the action to perform before completing the returned CompletionStageCompletionStage<Void> acceptEitherAsync(CompletionStage<? extends T> other, Consumer<? super T> action, Executor executor)
CompletionStage
documentation for rules covering exceptional completion.other
- the other CompletionStageaction
- the action to perform before completing the returned CompletionStageexecutor
- the executor to use for asynchronous executionCompletionStage<Void> runAfterEither(CompletionStage<?> other, Runnable action)
CompletionStage
documentation for rules covering exceptional completion.other
- the other CompletionStageaction
- the action to perform before completing the returned CompletionStageCompletionStage<Void> runAfterEitherAsync(CompletionStage<?> other, Runnable action)
CompletionStage
documentation for rules covering exceptional completion.other
- the other CompletionStageaction
- the action to perform before completing the returned CompletionStageCompletionStage<Void> runAfterEitherAsync(CompletionStage<?> other, Runnable action, Executor executor)
CompletionStage
documentation for rules covering exceptional completion.other
- the other CompletionStageaction
- the action to perform before completing the returned CompletionStageexecutor
- the executor to use for asynchronous execution<U> CompletionStage<U> thenCompose(Function<? super T,? extends CompletionStage<U>> fn)
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.
U
- the type of the returned CompletionStage's resultfn
- the function to use to compute another CompletionStage<U> CompletionStage<U> thenComposeAsync(Function<? super T,? extends CompletionStage<U>> fn)
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.
U
- the type of the returned CompletionStage's resultfn
- the function to use to compute another CompletionStage<U> CompletionStage<U> thenComposeAsync(Function<? super T,? extends CompletionStage<U>> fn, Executor 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.
U
- the type of the returned CompletionStage's resultfn
- the function to use to compute another CompletionStageexecutor
- the executor to use for asynchronous execution<U> CompletionStage<U> handle(BiFunction<? super T,Throwable,? extends U> fn)
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.
U
- the function's return typefn
- the function to use to compute the value of the returned CompletionStage<U> CompletionStage<U> handleAsync(BiFunction<? super T,Throwable,? extends U> fn)
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.
U
- the function's return typefn
- the function to use to compute the value of the returned CompletionStage<U> CompletionStage<U> handleAsync(BiFunction<? super T,Throwable,? extends U> fn, Executor executor)
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.
U
- the function's return typefn
- the function to use to compute the value of the returned CompletionStageexecutor
- the executor to use for asynchronous executionCompletionStage<T> whenComplete(BiConsumer<? super T,? super Throwable> action)
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.
action
- the action to performCompletionStage<T> whenCompleteAsync(BiConsumer<? super T,? super Throwable> action)
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.
action
- the action to performCompletionStage<T> whenCompleteAsync(BiConsumer<? super T,? super Throwable> action, Executor executor)
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.
action
- the action to performexecutor
- the executor to use for asynchronous executionCompletionStage<T> exceptionally(Function<Throwable,? extends T> fn)
fn
- the function to use to compute the value of the returned CompletionStage if this CompletionStage completed exceptionallydefault CompletionStage<T> exceptionallyAsync(Function<Throwable,? extends T> fn)
handle(java.util.function.BiFunction<? super T, java.lang.Throwable, ? extends U>)
, relaying to handleAsync(java.util.function.BiFunction<? super T, java.lang.Throwable, ? extends U>)
on exception, then thenCompose(java.util.function.Function<? super T, ? extends java.util.concurrent.CompletionStage<U>>)
for result.fn
- the function to use to compute the value of the returned CompletionStage if this CompletionStage completed exceptionallydefault CompletionStage<T> exceptionallyAsync(Function<Throwable,? extends T> fn, Executor executor)
handle(java.util.function.BiFunction<? super T, java.lang.Throwable, ? extends U>)
, relaying to handleAsync(java.util.function.BiFunction<? super T, java.lang.Throwable, ? extends U>)
on exception, then thenCompose(java.util.function.Function<? super T, ? extends java.util.concurrent.CompletionStage<U>>)
for result.fn
- the function to use to compute the value of the returned CompletionStage if this CompletionStage completed exceptionallyexecutor
- the executor to use for asynchronous executiondefault CompletionStage<T> exceptionallyCompose(Function<Throwable,? extends CompletionStage<T>> fn)
handle(java.util.function.BiFunction<? super T, java.lang.Throwable, ? extends U>)
, invoking the given function on exception, then thenCompose(java.util.function.Function<? super T, ? extends java.util.concurrent.CompletionStage<U>>)
for result.fn
- the function to use to compute the returned CompletionStage if this CompletionStage completed exceptionallydefault CompletionStage<T> exceptionallyComposeAsync(Function<Throwable,? extends CompletionStage<T>> fn)
handle(java.util.function.BiFunction<? super T, java.lang.Throwable, ? extends U>)
, relaying to handleAsync(java.util.function.BiFunction<? super T, java.lang.Throwable, ? extends U>)
on exception, then thenCompose(java.util.function.Function<? super T, ? extends java.util.concurrent.CompletionStage<U>>)
for result.fn
- the function to use to compute the returned CompletionStage if this CompletionStage completed exceptionallydefault CompletionStage<T> exceptionallyComposeAsync(Function<Throwable,? extends CompletionStage<T>> fn, Executor executor)
handle(java.util.function.BiFunction<? super T, java.lang.Throwable, ? extends U>)
, relaying to handleAsync(java.util.function.BiFunction<? super T, java.lang.Throwable, ? extends U>)
on exception, then thenCompose(java.util.function.Function<? super T, ? extends java.util.concurrent.CompletionStage<U>>)
for result.fn
- the function to use to compute the returned CompletionStage if this CompletionStage completed exceptionallyexecutor
- the executor to use for asynchronous executionCompletableFuture<T> toCompletableFuture()
CompletableFuture
maintaining the same completion properties as this stage. If this stage is already a CompletableFuture, this method may return this stage itself. Otherwise, invocation of this method may be equivalent in effect to thenApply(x -> x)
, but returning an instance of type CompletableFuture
.
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/concurrent/CompletionStage.html