Promise

A Java library for JavaScript-like Promise.

Why Promise?

• The CompletableFuture interface is complicated while JavaScript Promise is simple and probably more familiar.
• CompletableFuture isn't available until Android Nougat and android-retrofuture is too heavy-weight for just a couple of simple use cases.
• A bring-your-own-thread implementation, without the overhead of a ForkJoinPool.

Integration

dependencies {
    implementation 'me.zhanghai.java.promise:library:1.0.0'
}

Usage

Much like the JavaScript Promise. You can check out Promise.java for its exact interface, and the main difference is that a Settler object is used to provide resolve() and reject().

For example:

int size = new Promise<Integer>(settler -> mHandler.post(() -> {
    try {
        int size_ = mCallback.onRead(offset[0], buffer.length, buffer);
        settler.resolve(size_);
    } catch (Exception e) {
        settler.reject(e);
    }
})).await();

Caveat

The executable passed to Promise constructor is executed immediately, unlike in JavaScript where it will be executed after the current frame. This is because there isn't a generic way to do this in Java, and this way the behavior is still simple and deterministic.

License

Copyright 2019 Hai Zhang

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.