com.firefly.utils.concurrent.Promise Maven / Gradle / Ivy
package com.firefly.utils.concurrent;
import java.util.Objects;
import java.util.concurrent.CompletableFuture;
/**
* 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) {
}
}
/**
* 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
* @param the type of the result
* @return a promise that when completed, completes the given CompletableFuture
*/
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;
}
}
}