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Introduce FutureUtils to reduce duplicated code around CompletableFut…
…ure (PegaSysEng#868)
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util/src/main/java/tech/pegasys/pantheon/util/FutureUtils.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,87 @@ | ||
| /* | ||
| * Copyright 2019 ConsenSys AG. | ||
| * | ||
| * 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 tech.pegasys.pantheon.util; | ||
|
|
||
| import static java.util.concurrent.CompletableFuture.completedFuture; | ||
|
|
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| import java.util.concurrent.CompletableFuture; | ||
| import java.util.concurrent.CompletionStage; | ||
| import java.util.function.Function; | ||
|
|
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| public class FutureUtils { | ||
|
|
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| /** | ||
| * Creates a {@link CompletableFuture} that is exceptionally completed by <code>error</code>. | ||
| * | ||
| * @param error the error to exceptionally complete the future with | ||
| * @param <T> the type of CompletableFuture | ||
| * @return a CompletableFuture exceptionally completed by <code>error</code>. | ||
| */ | ||
| public static <T> CompletableFuture<T> completedExceptionally(final Throwable error) { | ||
| final CompletableFuture<T> future = new CompletableFuture<>(); | ||
| future.completeExceptionally(error); | ||
| return future; | ||
| } | ||
|
|
||
| /** | ||
| * Returns a new CompletionStage that, when the provided stage completes exceptionally, is | ||
| * executed with the provided stage's exception as the argument to the supplied function. | ||
| * Otherwise the returned stage completes successfully with the same value as the provided stage. | ||
| * | ||
| * <p>This is the exceptional equivalent to {@link CompletionStage#thenCompose(Function)} | ||
| * | ||
| * @param future the future to handle results or exceptions from | ||
| * @param errorHandler the function returning a new CompletionStage | ||
| * @param <T> the type of the CompletionStage's result | ||
| * @return the CompletionStage | ||
| */ | ||
| public static <T> CompletableFuture<T> exceptionallyCompose( | ||
| final CompletableFuture<T> future, | ||
| final Function<Throwable, CompletionStage<T>> errorHandler) { | ||
| final CompletableFuture<T> result = new CompletableFuture<>(); | ||
| future.whenComplete( | ||
| (value, error) -> { | ||
| try { | ||
| final CompletionStage<T> nextStep = | ||
| error != null ? errorHandler.apply(error) : completedFuture(value); | ||
| propagateResult(nextStep, result); | ||
| } catch (final Throwable t) { | ||
| result.completeExceptionally(t); | ||
| } | ||
| }); | ||
| return result; | ||
| } | ||
|
|
||
| /** | ||
| * Propagates the result of one {@link CompletionStage} to a different {@link CompletableFuture}. | ||
| * | ||
| * <p>When <code>from</code> completes successfully, <code>to</code> will be completed | ||
| * successfully with the same value. When <code>from</code> completes exceptionally, <code>to | ||
| * </code> will be completed exceptionally with the same exception. | ||
| * | ||
| * @param from the CompletionStage to take results and exceptions from | ||
| * @param to the CompletableFuture to propagate results and exceptions to | ||
| * @param <T> the type of the success value | ||
| */ | ||
| public static <T> void propagateResult( | ||
| final CompletionStage<T> from, final CompletableFuture<T> to) { | ||
| from.whenComplete( | ||
| (value, error) -> { | ||
| if (error != null) { | ||
| to.completeExceptionally(error); | ||
| } else { | ||
| to.complete(value); | ||
| } | ||
| }); | ||
| } | ||
| } |
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