org.eclipse.jetty.util.Promise Maven / Gradle / Ivy
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//
// ========================================================================
// Copyright (c) 1995-2018 Mort Bay Consulting Pty. Ltd.
// ------------------------------------------------------------------------
// All rights reserved. This program and the accompanying materials
// are made available under the terms of the Eclipse Public License v1.0
// and Apache License v2.0 which accompanies this distribution.
//
// The Eclipse Public License is available at
// http://www.eclipse.org/legal/epl-v10.html
//
// The Apache License v2.0 is available at
// http://www.opensource.org/licenses/apache2.0.php
//
// You may elect to redistribute this code under either of these licenses.
// ========================================================================
//
package org.eclipse.jetty.util;
import java.util.Objects;
import java.util.concurrent.CompletableFuture;
import org.eclipse.jetty.util.log.Log;
/**
* A callback abstraction that handles completed/failed events of asynchronous operations.
*
* @param the type of the context object
*/
public interface Promise
{
/**
* Callback invoked when the operation completes.
*
* @param result the context
* @see #failed(Throwable)
*/
default void succeeded(C result)
{
}
/**
* Callback invoked when the operation fails.
*
* @param x the reason for the operation failure
*/
default void failed(Throwable x)
{
}
/**
* Empty implementation of {@link Promise}.
*
* @param the type of the result
*/
class Adapter implements Promise
{
@Override
public void failed(Throwable x)
{
Log.getLogger(this.getClass()).warn(x);
}
}
/**
* Creates a promise from the given incomplete CompletableFuture.
* When the promise completes, either succeeding or failing, the
* CompletableFuture is also completed, respectively via
* {@link CompletableFuture#complete(Object)} or
* {@link CompletableFuture#completeExceptionally(Throwable)}.
*
* @param completable the CompletableFuture to convert into a promise
* @return a promise that when completed, completes the given CompletableFuture
* @param the type of the result
*/
static Promise from(CompletableFuture completable)
{
if (completable instanceof Promise)
return (Promise)completable;
return new Promise()
{
@Override
public void succeeded(T result)
{
completable.complete(result);
}
@Override
public void failed(Throwable x)
{
completable.completeExceptionally(x);
}
};
}
/**
* A CompletableFuture that is also a Promise.
*
* @param the type of the result
*/
class Completable extends CompletableFuture implements Promise
{
@Override
public void succeeded(S result)
{
complete(result);
}
@Override
public void failed(Throwable x)
{
completeExceptionally(x);
}
}
class Wrapper implements Promise
{
private final Promise promise;
public Wrapper(Promise promise)
{
this.promise = Objects.requireNonNull(promise);
}
@Override
public void succeeded(W result)
{
promise.succeeded(result);
}
@Override
public void failed(Throwable x)
{
promise.failed(x);
}
public Promise getPromise()
{
return promise;
}
public Promise unwrap()
{
Promise result = promise;
while (true)
{
if (result instanceof Wrapper)
result = ((Wrapper)result).unwrap();
else
break;
}
return result;
}
}
}