ratpack.exec.Promise Maven / Gradle / Ivy
/*
* Copyright 2014 the original author or 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 ratpack.exec;
import ratpack.func.Action;
/**
* A promise for a value that will be available later.
*
* A promise allows what is to be done with the value to be specified without having the value available.
* They are a common alternative to callbacks in asynchronous programming.
*
*
Testing
*
* To test code that uses promises, see the {@code ratpack.test.exec.ExecHarness} class.
*
* @param the type of promised value
*/
public interface Promise extends SuccessPromise {
/**
* Specifies the action to take if the an error occurs trying to produce the promised value.
*
* @param errorHandler the action to take if an error occurs
* @return A promise for the successful result
*/
SuccessPromise onError(Action errorHandler);
/**
* {@inheritDoc}
*/
@Override
void then(Action then);
default void asResult(Action> resultHandler) {
onError(t -> resultHandler.execute(Result.failure(t))).then(v -> resultHandler.execute(Result.success(v)));
}
}