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Promises for Java

Promises for Java is a simple implementation of promises, based on the Promises/A+ proposal for JavaScript.

From that proposal:

A promise represents a value that may not be available yet. The primary method for interacting with a promise is its then method.

The goal is to simplify asynchronous flows, avoiding the so-called Callback Pyramid of Doom.

The major difference, besides strong type-checking brought/enforced by Java, is that the then method is not asynchronous: if the promise is already fulfilled or rejected, the callbacks will be called synchronously, before the method returns.

The implementation is inspired by Guava's Optional and SettableFuture, and includes a FuturePromise as a two-way bridge with Guava's ListenableFuture. The dependency on Guava is optional though (but then you won't bridge with futures).

License

Copyright 2013 Thomas Broyer

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.