Package com.google.common.util.concurrent

Class Futures

java.lang.Object
com.google.common.util.concurrent.Futures
@Beta @GwtCompatible(emulated=true) public final class Futures extends Object
Static utility methods pertaining to the Future interface.

Many of these methods use the ListenableFuture API; consult the Guava User Guide article on ListenableFuture.

Since:
1.0

  • Method Details

    • makeChecked

      @GwtIncompatible public static <V, X extends Exception> CheckedFuture<V,X> makeChecked(ListenableFuture<V> future, Function<? super Exception,X> mapper)
      Creates a CheckedFuture out of a normal ListenableFuture and a Function that maps from Exception instances into the appropriate checked type.

      Warning: We recommend against using CheckedFuture in new projects. CheckedFuture is difficult to build libraries atop. CheckedFuture ports of methods like transformAsync(com.google.common.util.concurrent.ListenableFuture<I>, com.google.common.util.concurrent.AsyncFunction<? super I, ? extends O>) have historically had bugs, and some of these bugs are necessary, unavoidable consequences of the CheckedFuture API. Additionally, CheckedFuture encourages users to take exceptions from one thread and rethrow them in another, producing confusing stack traces.

      The given mapping function will be applied to an InterruptedException, a CancellationException, or an ExecutionException. See Future.get() for details on the exceptions thrown.

      Since:
      9.0 (source-compatible since 1.0)

    • immediateFuture

      public static <V> ListenableFuture<V> immediateFuture(@Nullable V value)
      Creates a ListenableFuture which has its value set immediately upon construction. The getters just return the value. This Future can't be canceled or timed out and its isDone() method always returns true.

    • immediateCheckedFuture

      @GwtIncompatible public static <V, X extends Exception> CheckedFuture<V,X> immediateCheckedFuture(@Nullable V value)
      Returns a CheckedFuture which has its value set immediately upon construction.

      The returned Future can't be cancelled, and its isDone() method always returns true. Calling get() or checkedGet() will immediately return the provided value.

    • immediateFailedFuture

      public static <V> ListenableFuture<V> immediateFailedFuture(Throwable throwable)
      Returns a ListenableFuture which has an exception set immediately upon construction.

      The returned Future can't be cancelled, and its isDone() method always returns true. Calling get() will immediately throw the provided Throwable wrapped in an ExecutionException.

    • immediateCancelledFuture

      public static <V> ListenableFuture<V> immediateCancelledFuture()
      Creates a ListenableFuture which is cancelled immediately upon construction, so that isCancelled() always returns true.
      Since:
      14.0

    • immediateFailedCheckedFuture

      @GwtIncompatible public static <V, X extends Exception> CheckedFuture<V,X> immediateFailedCheckedFuture(X exception)
      Returns a CheckedFuture which has an exception set immediately upon construction.

      The returned Future can't be cancelled, and its isDone() method always returns true. Calling get() will immediately throw the provided Exception wrapped in an ExecutionException, and calling checkedGet() will throw the provided exception itself.

    • catching

      @GwtIncompatible("AVAILABLE but requires exceptionType to be Throwable.class") public static <V, X extends Throwable> ListenableFuture<V> catching(ListenableFuture<? extends V> input, Class<X> exceptionType, Function<? super X,? extends V> fallback)
      Returns a Future whose result is taken from the given primary input or, if the primary input fails with the given exceptionType, from the result provided by the fallback. Function.apply(F) is not invoked until the primary input has failed, so if the primary input succeeds, it is never invoked. If, during the invocation of fallback, an exception is thrown, this exception is used as the result of the output Future.

      Usage example: 

         
   ListenableFuture<Integer> fetchCounterFuture = ...;

   // Falling back to a zero counter in case an exception happens when
   // processing the RPC to fetch counters.
   ListenableFuture<Integer> faultTolerantFuture = Futures.catching(
       fetchCounterFuture, FetchException.class,
       new Function<FetchException, Integer>() {
         public Integer apply(FetchException e) {
           return 0;
         }
       });

      This overload, which does not accept an executor, uses directExecutor, a dangerous choice in some cases. See the discussion in the ListenableFuture.addListener documentation. The documentation's warnings about "lightweight listeners" refer here to the work done during Function.apply.

      Parameters:
      input - the primary input Future
      exceptionType - the exception type that triggers use of fallback. The exception type is matched against the input's exception. "The input's exception" means the cause of the ExecutionException thrown by input.get() or, if get() throws a different kind of exception, that exception itself. To avoid hiding bugs and other unrecoverable errors, callers should prefer more specific types, avoiding Throwable.class in particular.
      fallback - the Function to be called if input fails with the expected exception type. The function's argument is the input's exception. "The input's exception" means the cause of the ExecutionException thrown by input.get() or, if get() throws a different kind of exception, that exception itself.
      Since:
      19.0

    • catching

      @GwtIncompatible("AVAILABLE but requires exceptionType to be Throwable.class") public static <V, X extends Throwable> ListenableFuture<V> catching(ListenableFuture<? extends V> input, Class<X> exceptionType, Function<? super X,? extends V> fallback, Executor executor)
      Returns a Future whose result is taken from the given primary input or, if the primary input fails with the given exceptionType, from the result provided by the fallback. Function.apply(F) is not invoked until the primary input has failed, so if the primary input succeeds, it is never invoked. If, during the invocation of fallback, an exception is thrown, this exception is used as the result of the output Future.

      Usage example: 

         
   ListenableFuture<Integer> fetchCounterFuture = ...;

   // Falling back to a zero counter in case an exception happens when
   // processing the RPC to fetch counters.
   ListenableFuture<Integer> faultTolerantFuture = Futures.catching(
       fetchCounterFuture, FetchException.class,
       new Function<FetchException, Integer>() {
         public Integer apply(FetchException e) {
           return 0;
         }
       }, directExecutor());

      When selecting an executor, note that directExecutor is dangerous in some cases. See the discussion in the ListenableFuture.addListener documentation. The documentation's warnings about "lightweight listeners" refer here to the work done during Function.apply.

      Parameters:
      input - the primary input Future
      exceptionType - the exception type that triggers use of fallback. The exception type is matched against the input's exception. "The input's exception" means the cause of the ExecutionException thrown by input.get() or, if get() throws a different kind of exception, that exception itself. To avoid hiding bugs and other unrecoverable errors, callers should prefer more specific types, avoiding Throwable.class in particular.
      fallback - the Function to be called if input fails with the expected exception type. The function's argument is the input's exception. "The input's exception" means the cause of the ExecutionException thrown by input.get() or, if get() throws a different kind of exception, that exception itself.
      executor - the executor that runs fallback if input fails
      Since:
      19.0

    • catchingAsync

      @GwtIncompatible("AVAILABLE but requires exceptionType to be Throwable.class") public static <V, X extends Throwable> ListenableFuture<V> catchingAsync(ListenableFuture<? extends V> input, Class<X> exceptionType, AsyncFunction<? super X,? extends V> fallback)
      Returns a Future whose result is taken from the given primary input or, if the primary input fails with the given exceptionType, from the result provided by the fallback. AsyncFunction.apply(I) is not invoked until the primary input has failed, so if the primary input succeeds, it is never invoked. If, during the invocation of fallback, an exception is thrown, this exception is used as the result of the output Future.

      Usage examples: 

         
   ListenableFuture<Integer> fetchCounterFuture = ...;

   // Falling back to a zero counter in case an exception happens when
   // processing the RPC to fetch counters.
   ListenableFuture<Integer> faultTolerantFuture = Futures.catchingAsync(
       fetchCounterFuture, FetchException.class,
       new AsyncFunction<FetchException, Integer>() {
         public ListenableFuture<Integer> apply(FetchException e) {
           return immediateFuture(0);
         }
       });

      The fallback can also choose to propagate the original exception when desired: 

         
   ListenableFuture<Integer> fetchCounterFuture = ...;

   // Falling back to a zero counter only in case the exception was a
   // TimeoutException.
   ListenableFuture<Integer> faultTolerantFuture = Futures.catchingAsync(
       fetchCounterFuture, FetchException.class,
       new AsyncFunction<FetchException, Integer>() {
         public ListenableFuture<Integer> apply(FetchException e)
             throws FetchException {
           if (omitDataOnFetchFailure) {
             return immediateFuture(0);
           }
           throw e;
         }
       });

      This overload, which does not accept an executor, uses directExecutor, a dangerous choice in some cases. See the discussion in the ListenableFuture.addListener documentation. The documentation's warnings about "lightweight listeners" refer here to the work done during AsyncFunction.apply, not to any work done to complete the returned Future.

      Parameters:
      input - the primary input Future
      exceptionType - the exception type that triggers use of fallback. The exception type is matched against the input's exception. "The input's exception" means the cause of the ExecutionException thrown by input.get() or, if get() throws a different kind of exception, that exception itself. To avoid hiding bugs and other unrecoverable errors, callers should prefer more specific types, avoiding Throwable.class in particular.
      fallback - the AsyncFunction to be called if input fails with the expected exception type. The function's argument is the input's exception. "The input's exception" means the cause of the ExecutionException thrown by input.get() or, if get() throws a different kind of exception, that exception itself.
      Since:
      19.0 (similar functionality in 14.0 as withFallback)

    • catchingAsync

      @GwtIncompatible("AVAILABLE but requires exceptionType to be Throwable.class") public static <V, X extends Throwable> ListenableFuture<V> catchingAsync(ListenableFuture<? extends V> input, Class<X> exceptionType, AsyncFunction<? super X,? extends V> fallback, Executor executor)
      Returns a Future whose result is taken from the given primary input or, if the primary input fails with the given exceptionType, from the result provided by the fallback. AsyncFunction.apply(I) is not invoked until the primary input has failed, so if the primary input succeeds, it is never invoked. If, during the invocation of fallback, an exception is thrown, this exception is used as the result of the output Future.

      Usage examples: 

         
   ListenableFuture<Integer> fetchCounterFuture = ...;

   // Falling back to a zero counter in case an exception happens when
   // processing the RPC to fetch counters.
   ListenableFuture<Integer> faultTolerantFuture = Futures.catchingAsync(
       fetchCounterFuture, FetchException.class,
       new AsyncFunction<FetchException, Integer>() {
         public ListenableFuture<Integer> apply(FetchException e) {
           return immediateFuture(0);
         }
       }, directExecutor());

      The fallback can also choose to propagate the original exception when desired: 

         
   ListenableFuture<Integer> fetchCounterFuture = ...;

   // Falling back to a zero counter only in case the exception was a
   // TimeoutException.
   ListenableFuture<Integer> faultTolerantFuture = Futures.catchingAsync(
       fetchCounterFuture, FetchException.class,
       new AsyncFunction<FetchException, Integer>() {
         public ListenableFuture<Integer> apply(FetchException e)
             throws FetchException {
           if (omitDataOnFetchFailure) {
             return immediateFuture(0);
           }
           throw e;
         }
       }, directExecutor());

      When selecting an executor, note that directExecutor is dangerous in some cases. See the discussion in the ListenableFuture.addListener documentation. The documentation's warnings about "lightweight listeners" refer here to the work done during AsyncFunction.apply, not to any work done to complete the returned Future.

      Parameters:
      input - the primary input Future
      exceptionType - the exception type that triggers use of fallback. The exception type is matched against the input's exception. "The input's exception" means the cause of the ExecutionException thrown by input.get() or, if get() throws a different kind of exception, that exception itself. To avoid hiding bugs and other unrecoverable errors, callers should prefer more specific types, avoiding Throwable.class in particular.
      fallback - the AsyncFunction to be called if input fails with the expected exception type. The function's argument is the input's exception. "The input's exception" means the cause of the ExecutionException thrown by input.get() or, if get() throws a different kind of exception, that exception itself.
      executor - the executor that runs fallback if input fails
      Since:
      19.0 (similar functionality in 14.0 as withFallback)

    • withTimeout

      @GwtIncompatible public static <V> ListenableFuture<V> withTimeout(ListenableFuture<V> delegate, long time, TimeUnit unit, ScheduledExecutorService scheduledExecutor)
      Returns a future that delegates to another but will finish early (via a TimeoutException wrapped in an ExecutionException) if the specified duration expires.

      The delegate future is interrupted and cancelled if it times out.

      Parameters:
      delegate - The future to delegate to.
      time - when to timeout the future
      unit - the time unit of the time parameter
      scheduledExecutor - The executor service to enforce the timeout.
      Since:
      19.0

    • transformAsync

      public static <I, O> ListenableFuture<O> transformAsync(ListenableFuture<I> input, AsyncFunction<? super I,? extends O> function)
      Returns a new Future whose result is asynchronously derived from the result of the given Future. If the given Future fails, the returned Future fails with the same exception (and the function is not invoked).

      More precisely, the returned Future takes its result from a Future produced by applying the given AsyncFunction to the result of the original Future. Example usage: 

         
   ListenableFuture<RowKey> rowKeyFuture = indexService.lookUp(query);
   AsyncFunction<RowKey, QueryResult> queryFunction =
       new AsyncFunction<RowKey, QueryResult>() {
         public ListenableFuture<QueryResult> apply(RowKey rowKey) {
           return dataService.read(rowKey);
         }
       };
   ListenableFuture<QueryResult> queryFuture =
       transformAsync(rowKeyFuture, queryFunction);

      This overload, which does not accept an executor, uses directExecutor, a dangerous choice in some cases. See the discussion in the ListenableFuture.addListener documentation. The documentation's warnings about "lightweight listeners" refer here to the work done during AsyncFunction.apply, not to any work done to complete the returned Future.

      The returned Future attempts to keep its cancellation state in sync with that of the input future and that of the future returned by the function. That is, if the returned Future is cancelled, it will attempt to cancel the other two, and if either of the other two is cancelled, the returned Future will receive a callback in which it will attempt to cancel itself.

      Parameters:
      input - The future to transform
      function - A function to transform the result of the input future to the result of the output future
      Returns:
      A future that holds result of the function (if the input succeeded) or the original input's failure (if not)
      Since:
      19.0 (in 11.0 as transform)

    • transformAsync

      public static <I, O> ListenableFuture<O> transformAsync(ListenableFuture<I> input, AsyncFunction<? super I,? extends O> function, Executor executor)
      Returns a new Future whose result is asynchronously derived from the result of the given Future. If the given Future fails, the returned Future fails with the same exception (and the function is not invoked).

      More precisely, the returned Future takes its result from a Future produced by applying the given AsyncFunction to the result of the original Future. Example usage: 

         
   ListenableFuture<RowKey> rowKeyFuture = indexService.lookUp(query);
   AsyncFunction<RowKey, QueryResult> queryFunction =
       new AsyncFunction<RowKey, QueryResult>() {
         public ListenableFuture<QueryResult> apply(RowKey rowKey) {
           return dataService.read(rowKey);
         }
       };
   ListenableFuture<QueryResult> queryFuture =
       transformAsync(rowKeyFuture, queryFunction, executor);

      When selecting an executor, note that directExecutor is dangerous in some cases. See the discussion in the ListenableFuture.addListener documentation. The documentation's warnings about "lightweight listeners" refer here to the work done during AsyncFunction.apply, not to any work done to complete the returned Future.

      The returned Future attempts to keep its cancellation state in sync with that of the input future and that of the future returned by the chain function. That is, if the returned Future is cancelled, it will attempt to cancel the other two, and if either of the other two is cancelled, the returned Future will receive a callback in which it will attempt to cancel itself.

      Parameters:
      input - The future to transform
      function - A function to transform the result of the input future to the result of the output future
      executor - Executor to run the function in.
      Returns:
      A future that holds result of the function (if the input succeeded) or the original input's failure (if not)
      Since:
      19.0 (in 11.0 as transform)

    • transform

      public static <I, O> ListenableFuture<O> transform(ListenableFuture<I> input, Function<? super I,? extends O> function)
      Returns a new Future whose result is derived from the result of the given Future. If input fails, the returned Future fails with the same exception (and the function is not invoked). Example usage: 
         
   ListenableFuture<QueryResult> queryFuture = ...;
   Function<QueryResult, List<Row>> rowsFunction =
       new Function<QueryResult, List<Row>>() {
         public List<Row> apply(QueryResult queryResult) {
           return queryResult.getRows();
         }
       };
   ListenableFuture<List<Row>> rowsFuture =
       transform(queryFuture, rowsFunction);

      This overload, which does not accept an executor, uses directExecutor, a dangerous choice in some cases. See the discussion in the ListenableFuture.addListener documentation. The documentation's warnings about "lightweight listeners" refer here to the work done during Function.apply.

      The returned Future attempts to keep its cancellation state in sync with that of the input future. That is, if the returned Future is cancelled, it will attempt to cancel the input, and if the input is cancelled, the returned Future will receive a callback in which it will attempt to cancel itself.

      An example use of this method is to convert a serializable object returned from an RPC into a POJO.

      Parameters:
      input - The future to transform
      function - A Function to transform the results of the provided future to the results of the returned future. This will be run in the thread that notifies input it is complete.
      Returns:
      A future that holds result of the transformation.
      Since:
      9.0 (in 1.0 as compose)

    • transform

      public static <I, O> ListenableFuture<O> transform(ListenableFuture<I> input, Function<? super I,? extends O> function, Executor executor)
      Returns a new Future whose result is derived from the result of the given Future. If input fails, the returned Future fails with the same exception (and the function is not invoked). Example usage: 
         
   ListenableFuture<QueryResult> queryFuture = ...;
   Function<QueryResult, List<Row>> rowsFunction =
       new Function<QueryResult, List<Row>>() {
         public List<Row> apply(QueryResult queryResult) {
           return queryResult.getRows();
         }
       };
   ListenableFuture<List<Row>> rowsFuture =
       transform(queryFuture, rowsFunction, executor);

      When selecting an executor, note that directExecutor is dangerous in some cases. See the discussion in the ListenableFuture.addListener documentation. The documentation's warnings about "lightweight listeners" refer here to the work done during Function.apply.

      The returned Future attempts to keep its cancellation state in sync with that of the input future. That is, if the returned Future is cancelled, it will attempt to cancel the input, and if the input is cancelled, the returned Future will receive a callback in which it will attempt to cancel itself.

      An example use of this method is to convert a serializable object returned from an RPC into a POJO.

      Parameters:
      input - The future to transform
      function - A Function to transform the results of the provided future to the results of the returned future.
      executor - Executor to run the function in.
      Returns:
      A future that holds result of the transformation.
      Since:
      9.0 (in 2.0 as compose)

    • lazyTransform

      @GwtIncompatible public static <I, O> Future<O> lazyTransform(Future<I> input, Function<? super I,? extends O> function)
      Like transform(ListenableFuture, Function) except that the transformation function is invoked on each call to get() on the returned future.

      The returned Future reflects the input's cancellation state directly, and any attempt to cancel the returned Future is likewise passed through to the input Future.

      Note that calls to timed get only apply the timeout to the execution of the underlying Future, not to the execution of the transformation function.

      The primary audience of this method is callers of transform who don't have a ListenableFuture available and do not mind repeated, lazy function evaluation.

      Parameters:
      input - The future to transform
      function - A Function to transform the results of the provided future to the results of the returned future.
      Returns:
      A future that returns the result of the transformation.
      Since:
      10.0

    • dereference

      public static <V> ListenableFuture<V> dereference(ListenableFuture<? extends ListenableFuture<? extends V>> nested)
      Returns a new ListenableFuture whose result is the product of calling get() on the Future nested within the given Future, effectively chaining the futures one after the other. Example: 
         
   SettableFuture<ListenableFuture<String>> nested = SettableFuture.create();
   ListenableFuture<String> dereferenced = dereference(nested);

      Most users will not need this method. To create a Future that completes with the result of another Future, create a SettableFuture, and call setFuture(otherFuture) on it.

      dereference has the same cancellation and execution semantics as transformAsync(ListenableFuture, AsyncFunction), in that the returned Future attempts to keep its cancellation state in sync with both the input Future and the nested Future. The transformation is very lightweight and therefore takes place in the same thread (either the thread that called dereference, or the thread in which the dereferenced future completes).

      Parameters:
      nested - The nested future to transform.
      Returns:
      A future that holds result of the inner future.
      Since:
      13.0

    • allAsList

      @Beta @SafeVarargs public static <V> ListenableFuture<List<V>> allAsList(ListenableFuture<? extends V>... futures)
      Creates a new ListenableFuture whose value is a list containing the values of all its input futures, if all succeed. If any input fails, the returned future fails immediately.

      The list of results is in the same order as the input list.

      Canceling this future will attempt to cancel all the component futures, and if any of the provided futures fails or is canceled, this one is, too.

      Parameters:
      futures - futures to combine
      Returns:
      a future that provides a list of the results of the component futures
      Since:
      10.0

    • allAsList

      @Beta public static <V> ListenableFuture<List<V>> allAsList(Iterable<? extends ListenableFuture<? extends V>> futures)
      Creates a new ListenableFuture whose value is a list containing the values of all its input futures, if all succeed. If any input fails, the returned future fails immediately.

      The list of results is in the same order as the input list.

      Canceling this future will attempt to cancel all the component futures, and if any of the provided futures fails or is canceled, this one is, too.

      Parameters:
      futures - futures to combine
      Returns:
      a future that provides a list of the results of the component futures
      Since:
      10.0

    • whenAllComplete

      @SafeVarargs public static <V> Futures.FutureCombiner<V> whenAllComplete(ListenableFuture<? extends V>... futures)
      Creates a Futures.FutureCombiner that processes the completed futures whether or not they're successful.
      Since:
      20.0

    • whenAllComplete

      public static <V> Futures.FutureCombiner<V> whenAllComplete(Iterable<? extends ListenableFuture<? extends V>> futures)
      Creates a Futures.FutureCombiner that processes the completed futures whether or not they're successful.
      Since:
      20.0

    • whenAllSucceed

      @SafeVarargs public static <V> Futures.FutureCombiner<V> whenAllSucceed(ListenableFuture<? extends V>... futures)
      Creates a Futures.FutureCombiner requiring that all passed in futures are successful.

      If any input fails, the returned future fails immediately.

      Since:
      20.0

    • whenAllSucceed

      public static <V> Futures.FutureCombiner<V> whenAllSucceed(Iterable<? extends ListenableFuture<? extends V>> futures)
      Creates a Futures.FutureCombiner requiring that all passed in futures are successful.

      If any input fails, the returned future fails immediately.

      Since:
      20.0

    • nonCancellationPropagating

      public static <V> ListenableFuture<V> nonCancellationPropagating(ListenableFuture<V> future)
      Creates a new ListenableFuture whose result is set from the supplied future when it completes. Cancelling the supplied future will also cancel the returned future, but cancelling the returned future will have no effect on the supplied future.
      Since:
      15.0

    • successfulAsList

      @Beta @SafeVarargs public static <V> ListenableFuture<List<V>> successfulAsList(ListenableFuture<? extends V>... futures)
      Creates a new ListenableFuture whose value is a list containing the values of all its successful input futures. The list of results is in the same order as the input list, and if any of the provided futures fails or is canceled, its corresponding position will contain null (which is indistinguishable from the future having a successful value of null).

      Canceling this future will attempt to cancel all the component futures.

      Parameters:
      futures - futures to combine
      Returns:
      a future that provides a list of the results of the component futures
      Since:
      10.0

    • successfulAsList

      @Beta public static <V> ListenableFuture<List<V>> successfulAsList(Iterable<? extends ListenableFuture<? extends V>> futures)
      Creates a new ListenableFuture whose value is a list containing the values of all its successful input futures. The list of results is in the same order as the input list, and if any of the provided futures fails or is canceled, its corresponding position will contain null (which is indistinguishable from the future having a successful value of null).

      Canceling this future will attempt to cancel all the component futures.

      Parameters:
      futures - futures to combine
      Returns:
      a future that provides a list of the results of the component futures
      Since:
      10.0

    • inCompletionOrder

      @Beta @GwtIncompatible public static <T> ImmutableList<ListenableFuture<T>> inCompletionOrder(Iterable<? extends ListenableFuture<? extends T>> futures)
      Returns a list of delegate futures that correspond to the futures received in the order that they complete. Delegate futures return the same value or throw the same exception as the corresponding input future returns/throws.

      Cancelling a delegate future has no effect on any input future, since the delegate future does not correspond to a specific input future until the appropriate number of input futures have completed. At that point, it is too late to cancel the input future. The input future's result, which cannot be stored into the cancelled delegate future, is ignored.

      Since:
      17.0

    • addCallback

      public static <V> void addCallback(ListenableFuture<V> future, FutureCallback<? super V> callback)
      Registers separate success and failure callbacks to be run when the Future's computation is complete or, if the computation is already complete, immediately.

      There is no guaranteed ordering of execution of callbacks, but any callback added through this method is guaranteed to be called once the computation is complete. Example: 

       
 ListenableFuture<QueryResult> future = ...;
 addCallback(future,
     new FutureCallback<QueryResult>() {
       public void onSuccess(QueryResult result) {
         storeInCache(result);
       }
       public void onFailure(Throwable t) {
         reportError(t);
       }
     });

      This overload, which does not accept an executor, uses directExecutor, a dangerous choice in some cases. See the discussion in the ListenableFuture.addListener documentation.

      For a more general interface to attach a completion listener to a Future, see addListener.

      Parameters:
      future - The future attach the callback to.
      callback - The callback to invoke when future is completed.
      Since:
      10.0

    • addCallback

      public static <V> void addCallback(ListenableFuture<V> future, FutureCallback<? super V> callback, Executor executor)
      Registers separate success and failure callbacks to be run when the Future's computation is complete or, if the computation is already complete, immediately.

      The callback is run in executor. There is no guaranteed ordering of execution of callbacks, but any callback added through this method is guaranteed to be called once the computation is complete. Example: 

       
 ListenableFuture<QueryResult> future = ...;
 Executor e = ...
 addCallback(future,
     new FutureCallback<QueryResult>() {
       public void onSuccess(QueryResult result) {
         storeInCache(result);
       }
       public void onFailure(Throwable t) {
         reportError(t);
       }
     }, e);

      When selecting an executor, note that directExecutor is dangerous in some cases. See the discussion in the ListenableFuture.addListener documentation.

      For a more general interface to attach a completion listener to a Future, see addListener.

      Parameters:
      future - The future attach the callback to.
      callback - The callback to invoke when future is completed.
      executor - The executor to run callback when the future completes.
      Since:
      10.0

    • getDone

      public static <V> V getDone(Future<V> future) throws ExecutionException
      Returns the result of the input Future, which must have already completed.

      The benefits of this method are twofold. First, the name "getDone" suggests to readers that the Future is already done. Second, if buggy code calls getDone on a Future that is still pending, the program will throw instead of block. This can be important for APIs like whenAllComplete(...).call(...), where it is easy to use a new input from the call implementation but forget to add it to the arguments of whenAllComplete.

      If you are looking for a method to determine whether a given Future is done, use the instance method Future.isDone().

      Throws:
      ExecutionException - if the Future failed with an exception
      CancellationException - if the Future was cancelled
      IllegalStateException - if the Future is not done
      Since:
      20.0

    • getChecked

      @GwtIncompatible public static <V, X extends Exception> V getChecked(Future<V> future, Class<X> exceptionClass) throws X
      Returns the result of Future.get(), converting most exceptions to a new instance of the given checked exception type. This reduces boilerplate for a common use of Future in which it is unnecessary to programmatically distinguish between exception types or to extract other information from the exception instance.

      Exceptions from Future.get are treated as follows:

      The overall principle is to continue to treat every checked exception as a checked exception, every unchecked exception as an unchecked exception, and every error as an error. In addition, the cause of any ExecutionException is wrapped in order to ensure that the new stack trace matches that of the current thread.

      Instances of exceptionClass are created by choosing an arbitrary public constructor that accepts zero or more arguments, all of type String or Throwable (preferring constructors with at least one String) and calling the constructor via reflection. If the exception did not already have a cause, one is set by calling Throwable.initCause(Throwable) on it. If no such constructor exists, an IllegalArgumentException is thrown.

      Throws:
      X - if get throws any checked exception except for an ExecutionException whose cause is not itself a checked exception
      UncheckedExecutionException - if get throws an ExecutionException with a RuntimeException as its cause
      ExecutionError - if get throws an ExecutionException with an Error as its cause
      CancellationException - if get throws a CancellationException
      IllegalArgumentException - if exceptionClass extends RuntimeException or does not have a suitable constructor
      Since:
      19.0 (in 10.0 as get)

    • getChecked

      @GwtIncompatible public static <V, X extends Exception> V getChecked(Future<V> future, Class<X> exceptionClass, long timeout, TimeUnit unit) throws X
      Returns the result of Future.get(long, TimeUnit), converting most exceptions to a new instance of the given checked exception type. This reduces boilerplate for a common use of Future in which it is unnecessary to programmatically distinguish between exception types or to extract other information from the exception instance.

      Exceptions from Future.get are treated as follows:

      The overall principle is to continue to treat every checked exception as a checked exception, every unchecked exception as an unchecked exception, and every error as an error. In addition, the cause of any ExecutionException is wrapped in order to ensure that the new stack trace matches that of the current thread.

      Instances of exceptionClass are created by choosing an arbitrary public constructor that accepts zero or more arguments, all of type String or Throwable (preferring constructors with at least one String) and calling the constructor via reflection. If the exception did not already have a cause, one is set by calling Throwable.initCause(Throwable) on it. If no such constructor exists, an IllegalArgumentException is thrown.

      Throws:
      X - if get throws any checked exception except for an ExecutionException whose cause is not itself a checked exception
      UncheckedExecutionException - if get throws an ExecutionException with a RuntimeException as its cause
      ExecutionError - if get throws an ExecutionException with an Error as its cause
      CancellationException - if get throws a CancellationException
      IllegalArgumentException - if exceptionClass extends RuntimeException or does not have a suitable constructor
      Since:
      19.0 (in 10.0 as get and with different parameter order)

    • getUnchecked

      @GwtIncompatible public static <V> V getUnchecked(Future<V> future)
      Returns the result of calling Future.get() uninterruptibly on a task known not to throw a checked exception. This makes Future more suitable for lightweight, fast-running tasks that, barring bugs in the code, will not fail. This gives it exception-handling behavior similar to that of ForkJoinTask.join.

      Exceptions from Future.get are treated as follows:

      The overall principle is to eliminate all checked exceptions: to loop to avoid InterruptedException, to pass through CancellationException, and to wrap any exception from the underlying computation in an UncheckedExecutionException or ExecutionError.

      For an uninterruptible get that preserves other exceptions, see Uninterruptibles.getUninterruptibly(Future).

      Throws:
      UncheckedExecutionException - if get throws an ExecutionException with an Exception as its cause
      ExecutionError - if get throws an ExecutionException with an Error as its cause
      CancellationException - if get throws a CancellationException
      Since:
      10.0