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/*
* Copyright (C) 2006 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
* in compliance with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License
* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
* or implied. See the License for the specific language governing permissions and limitations under
* the License.
*/
package com.google.common.util.concurrent;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Function;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
/**
* A {@link ListenableFuture} that supports fluent chains of operations. For example:
*
* {@code
* ListenableFuture adminIsLoggedIn =
* FluentFuture.from(usersDatabase.getAdminUser())
* .transform(User::getId, directExecutor())
* .transform(ActivityService::isLoggedIn, threadPool)
* .catching(RpcException.class, e -> false, directExecutor());
* }
*
* Alternatives
*
* Frameworks
*
* When chaining together a graph of asynchronous operations, you will often find it easier to
* use a framework. Frameworks automate the process, often adding features like monitoring,
* debugging, and cancellation. Examples of frameworks include:
*
*
* - Dagger Producers
*
*
* {@link java.util.concurrent.CompletableFuture} / {@link java.util.concurrent.CompletionStage}
*
*
* Users of {@code CompletableFuture} will likely want to continue using {@code
* CompletableFuture}. {@code FluentFuture} is targeted at people who use {@code ListenableFuture},
* who can't use Java 8, or who want an API more focused than {@code CompletableFuture}. (If you
* need to adapt between {@code CompletableFuture} and {@code ListenableFuture}, consider Future Converter.)
*
*
Extension
*
* If you want a class like {@code FluentFuture} but with extra methods, we recommend declaring your
* own subclass of {@link ListenableFuture}, complete with a method like {@link #from} to adapt an
* existing {@code ListenableFuture}, implemented atop a {@link ForwardingListenableFuture} that
* forwards to that future and adds the desired methods.
*
* @since 23.0
*/
@Beta
@GwtCompatible(emulated = true)
public abstract class FluentFuture extends GwtFluentFutureCatchingSpecialization {
FluentFuture() {}
/**
* Converts the given {@code ListenableFuture} to an equivalent {@code FluentFuture}.
*
* If the given {@code ListenableFuture} is already a {@code FluentFuture}, it is returned
* directly. If not, it is wrapped in a {@code FluentFuture} that delegates all calls to the
* original {@code ListenableFuture}.
*/
public static FluentFuture from(ListenableFuture future) {
return future instanceof FluentFuture
? (FluentFuture) future
: new ForwardingFluentFuture(future);
}
/**
* Returns a {@code Future} whose result is taken from this {@code Future} or, if this {@code
* Future} fails with the given {@code exceptionType}, from the result provided by the {@code
* fallback}. {@link Function#apply} is not invoked until the primary input has failed, so if the
* primary input succeeds, it is never invoked. If, during the invocation of {@code fallback}, an
* exception is thrown, this exception is used as the result of the output {@code Future}.
*
* Usage example:
*
*
{@code
* // Falling back to a zero counter in case an exception happens when processing the RPC to fetch
* // counters.
* ListenableFuture faultTolerantFuture =
* fetchCounters().catching(FetchException.class, x -> 0, directExecutor());
* }
*
* When selecting an executor, note that {@code directExecutor} is dangerous in some cases. See
* the discussion in the {@link #addListener} documentation. All its warnings about heavyweight
* listeners are also applicable to heavyweight functions passed to this method.
*
*
This method is similar to {@link java.util.concurrent.CompletableFuture#exceptionally}. It
* can also serve some of the use cases of {@link java.util.concurrent.CompletableFuture#handle}
* and {@link java.util.concurrent.CompletableFuture#handleAsync} when used along with {@link
* #transform}.
*
* @param exceptionType the exception type that triggers use of {@code fallback}. The exception
* type is matched against the input's exception. "The input's exception" means the cause of
* the {@link ExecutionException} thrown by {@code input.get()} or, if {@code 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 {@code
* Throwable.class} in particular.
* @param fallback the {@link Function} to be called if the 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 {@link ExecutionException} thrown by {@code this.get()} or, if
* {@code get()} throws a different kind of exception, that exception itself.
* @param executor the executor that runs {@code fallback} if the input fails
*/
@Partially.GwtIncompatible("AVAILABLE but requires exceptionType to be Throwable.class")
public final FluentFuture catching(
Class exceptionType, Function fallback, Executor executor) {
return (FluentFuture) Futures.catching(this, exceptionType, fallback, executor);
}
/**
* Returns a {@code Future} whose result is taken from this {@code Future} or, if this {@code
* Future} fails with the given {@code exceptionType}, from the result provided by the {@code
* fallback}. {@link AsyncFunction#apply} is not invoked until the primary input has failed, so if
* the primary input succeeds, it is never invoked. If, during the invocation of {@code fallback},
* an exception is thrown, this exception is used as the result of the output {@code Future}.
*
* Usage examples:
*
*
{@code
* // Falling back to a zero counter in case an exception happens when processing the RPC to fetch
* // counters.
* ListenableFuture faultTolerantFuture =
* fetchCounters().catchingAsync(
* FetchException.class, x -> immediateFuture(0), directExecutor());
* }
*
* The fallback can also choose to propagate the original exception when desired:
*
*
{@code
* // Falling back to a zero counter only in case the exception was a
* // TimeoutException.
* ListenableFuture faultTolerantFuture =
* fetchCounters().catchingAsync(
* FetchException.class,
* e -> {
* if (omitDataOnFetchFailure) {
* return immediateFuture(0);
* }
* throw e;
* },
* directExecutor());
* }
*
* When selecting an executor, note that {@code directExecutor} is dangerous in some cases. See
* the discussion in the {@link #addListener} documentation. All its warnings about heavyweight
* listeners are also applicable to heavyweight functions passed to this method. (Specifically,
* {@code directExecutor} functions should avoid heavyweight operations inside {@code
* AsyncFunction.apply}. Any heavyweight operations should occur in other threads responsible for
* completing the returned {@code Future}.)
*
*
This method is similar to {@link java.util.concurrent.CompletableFuture#exceptionally}. It
* can also serve some of the use cases of {@link java.util.concurrent.CompletableFuture#handle}
* and {@link java.util.concurrent.CompletableFuture#handleAsync} when used along with {@link
* #transform}.
*
* @param exceptionType the exception type that triggers use of {@code fallback}. The exception
* type is matched against the input's exception. "The input's exception" means the cause of
* the {@link ExecutionException} thrown by {@code this.get()} or, if {@code 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 {@code
* Throwable.class} in particular.
* @param fallback the {@link AsyncFunction} to be called if the 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 {@link ExecutionException} thrown by {@code input.get()} or, if
* {@code get()} throws a different kind of exception, that exception itself.
* @param executor the executor that runs {@code fallback} if the input fails
*/
@Partially.GwtIncompatible("AVAILABLE but requires exceptionType to be Throwable.class")
public final FluentFuture catchingAsync(
Class exceptionType, AsyncFunction fallback, Executor executor) {
return (FluentFuture) Futures.catchingAsync(this, exceptionType, fallback, executor);
}
/**
* Returns a future that delegates to this future but will finish early (via a {@link
* TimeoutException} wrapped in an {@link ExecutionException}) if the specified timeout expires.
* If the timeout expires, not only will the output future finish, but also the input future
* ({@code this}) will be cancelled and interrupted.
*
* @param timeout when to time out the future
* @param unit the time unit of the time parameter
* @param scheduledExecutor The executor service to enforce the timeout.
*/
@GwtIncompatible // ScheduledExecutorService
public final FluentFuture withTimeout(
long timeout, TimeUnit unit, ScheduledExecutorService scheduledExecutor) {
return (FluentFuture) Futures.withTimeout(this, timeout, unit, scheduledExecutor);
}
/**
* Returns a new {@code Future} whose result is asynchronously derived from the result of this
* {@code Future}. If the input {@code Future} fails, the returned {@code Future} fails with the
* same exception (and the function is not invoked).
*
* More precisely, the returned {@code Future} takes its result from a {@code Future} produced
* by applying the given {@code AsyncFunction} to the result of the original {@code Future}.
* Example usage:
*
*
{@code
* FluentFuture rowKeyFuture = FluentFuture.from(indexService.lookUp(query));
* ListenableFuture queryFuture =
* rowKeyFuture.transformAsync(dataService::readFuture, executor);
* }
*
* When selecting an executor, note that {@code directExecutor} is dangerous in some cases. See
* the discussion in the {@link #addListener} documentation. All its warnings about heavyweight
* listeners are also applicable to heavyweight functions passed to this method. (Specifically,
* {@code directExecutor} functions should avoid heavyweight operations inside {@code
* AsyncFunction.apply}. Any heavyweight operations should occur in other threads responsible for
* completing the returned {@code Future}.)
*
*
The returned {@code 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
* {@code Future} is cancelled, it will attempt to cancel the other two, and if either of the
* other two is cancelled, the returned {@code Future} will receive a callback in which it will
* attempt to cancel itself.
*
*
This method is similar to {@link java.util.concurrent.CompletableFuture#thenCompose} and
* {@link java.util.concurrent.CompletableFuture#thenComposeAsync}. It can also serve some of the
* use cases of {@link java.util.concurrent.CompletableFuture#handle} and {@link
* java.util.concurrent.CompletableFuture#handleAsync} when used along with {@link #catching}.
*
* @param function A function to transform the result of this future to the result of the output
* future
* @param executor Executor to run the function in.
* @return A future that holds result of the function (if the input succeeded) or the original
* input's failure (if not)
*/
public final FluentFuture transformAsync(
AsyncFunction function, Executor executor) {
return (FluentFuture) Futures.transformAsync(this, function, executor);
}
/**
* Returns a new {@code Future} whose result is derived from the result of this {@code Future}. If
* this input {@code Future} fails, the returned {@code Future} fails with the same exception (and
* the function is not invoked). Example usage:
*
* {@code
* ListenableFuture> rowsFuture =
* queryFuture.transform(QueryResult::getRows, executor);
* }
*
* When selecting an executor, note that {@code directExecutor} is dangerous in some cases. See
* the discussion in the {@link #addListener} documentation. All its warnings about heavyweight
* listeners are also applicable to heavyweight functions passed to this method.
*
*
The returned {@code Future} attempts to keep its cancellation state in sync with that of the
* input future. That is, if the returned {@code Future} is cancelled, it will attempt to cancel
* the input, and if the input is cancelled, the returned {@code 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.
*
*
This method is similar to {@link java.util.concurrent.CompletableFuture#thenApply} and
* {@link java.util.concurrent.CompletableFuture#thenApplyAsync}. It can also serve some of the
* use cases of {@link java.util.concurrent.CompletableFuture#handle} and {@link
* java.util.concurrent.CompletableFuture#handleAsync} when used along with {@link #catching}.
*
* @param function A Function to transform the results of this future to the results of the
* returned future.
* @param executor Executor to run the function in.
* @return A future that holds result of the transformation.
*/
public final FluentFuture transform(Function function, Executor executor) {
return (FluentFuture) Futures.transform(this, function, executor);
}
/**
* Registers separate success and failure callbacks to be run when this {@code Future}'s
* computation is {@linkplain java.util.concurrent.Future#isDone() complete} or, if the
* computation is already complete, immediately.
*
* The callback is run on {@code 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:
*
*
{@code
* future.addCallback(
* new FutureCallback() {
* public void onSuccess(QueryResult result) {
* storeInCache(result);
* }
* public void onFailure(Throwable t) {
* reportError(t);
* }
* }, executor);
* }
*
* When selecting an executor, note that {@code directExecutor} is dangerous in some cases. See
* the discussion in the {@link #addListener} documentation. All its warnings about heavyweight
* listeners are also applicable to heavyweight callbacks passed to this method.
*
*
For a more general interface to attach a completion listener, see {@link #addListener}.
*
*
This method is similar to {@link java.util.concurrent.CompletableFuture#whenComplete} and
* {@link java.util.concurrent.CompletableFuture#whenCompleteAsync}. It also serves the use case
* of {@link java.util.concurrent.CompletableFuture#thenAccept} and {@link
* java.util.concurrent.CompletableFuture#thenAcceptAsync}.
*
* @param callback The callback to invoke when this {@code Future} is completed.
* @param executor The executor to run {@code callback} when the future completes.
*/
public final void addCallback(FutureCallback callback, Executor executor) {
Futures.addCallback(this, callback, executor);
}
}