A Promise for android

A Promise library for android which follows Promise/A+ standard

Introduction

Nearly, all android promise open-source projects offer us a tool, which has async-thread-execution being involved into their component. I must say, it is good, since AsyncTask is just like that - executing tasks in a pre-built task-executors, or let user provide one for AsyncTask. But I think, Promise should just focus on async processing functions with callbacks, without making any extra thread or using executors to handle runnable or Callable process.

The Promise lib here dose not do any thread-making stuff, or not depends on any executors. It just produce a Deferred object, letting you decide when to resolve a deferred or reject a deferred. Then making then on a desired looper thread.

If you want your runnable to be running asynchronously, just make your own thread to take charge of running and remember to resolve or reject the result.

While in thenable method, you should supply us a resolver which can turn the promise result into another promise just like Promise in javascript.

And, The Promise lib here also provide us a lot of features that js promise owns too. Here is the example:

public class PromiseTest {

	public static void main(String...args) {
		Promise<Integer> p1 = Promise.make(new DirectFunction<Integer>() {

			@Override
			public void run(final Locker<Integer> locker) {
				new Thread() {
					public void run() {
						try {
							System.out.println("p1 is running");
							Thread.sleep(5000);
						} catch (InterruptedException e) {
							locker.reject(e);
						}
						locker.resolve(100);
						System.out.println("p1 is over");
					}
				}.start();
			}

		});


		Promise<Object> px = Promise.make(new DirectFunction<Object>() {
			@Override
			public void run(Locker<Object> locker) {
				locker.reject(new TimeoutException("timeout"));
			}
		}).exception(new ExceptionResolver<Object, TimeoutException>() {
			@Override
			public Object onCatch(TimeoutException exception) {
				exception.printStackTrace();
				throw Promise.newException(exception);
			}
		});

		px.exception(new ExceptionPromiseResolver<Object, InterruptedException>() {
			@Override
			public Promise<Object> onCatch(InterruptedException exception) {
				throw Promise.newException(new IOException());
			}
		});

		Promise<Integer> p1p = p1.clone();

		Promise<Integer> p2 = Promise.make(new DirectFunction<Integer>() {
			@Override
			public void run(final Locker<Integer> locker) {
				new Thread() {
					public void run() {
						try {
							System.out.println("p2 is running");
							Thread.sleep(4000);
						} catch (InterruptedException e) {
							locker.reject(e);
						}
						locker.resolve(100);
						System.out.println("p2 is over");
					}
				}.start();
			}
		});

		ArrayList<Promise<?>> list = new ArrayList<Promise<?>>();
		list.add(p1);
		list.add(p1p);
		list.add(p2);

		Promise.race(list).then(new DirectResolver<Object, Void>() {

			@Override
			public Void resolve(Object newValue) {
				System.out.println("race complete" + newValue);
				return null;
			}

			@Override
			public Void reject(Exception exception) {
				return null;
			}
		});

		p1.then(new DirectResolver<Integer, String>() {

			@Override
			public String resolve(Integer newValue) {
				System.out.println(newValue);
				return "p1 resolved";
			}

			@Override
			public String reject(Exception exception) {
				throw Promise.newException(exception);
			}
		}).then(new SimplePromiseResolver<String, Integer>() {

			@Override
			public Promise<Integer> resolve(String newValue) {
				System.out.println(newValue);
				return Promise.make(new DirectFunction<Integer>() {

					@Override
					public void run(final Locker<Integer> locker) {
						new Thread() {
							public void run() {
								try {
									Thread.sleep(5000);
								} catch (InterruptedException e) {
									locker.reject(e);
								}
								locker.resolve(3000);
							}
						}.start();
					}

				});
			}

		}).then(new SimpleResolver<Integer, Integer>() {

			@Override
			public Integer resolve(Integer newValue) {
				System.out.println("then resolve a new value=" + newValue);
				return null;
			}
		}).then(new SimpleResolver<Number, Integer>() {
			@Override
			public Integer resolve(Number newValue) {
				return null;
			}
		});

		// making a deferred, then use defer to propagate a promise
		final PromiseDeferred<Integer> defer = PromiseDeferred.make();

		final PromiseDeferred<String> defer2 = PromiseDeferred.make();




		defer.promise().then(new SimpleResolver<Integer, Void>() {
			@Override
			public Void resolve(Integer newValue) {
				System.out.println("Defer:::" + newValue);
				return null;
			}
		}).exception(new ExceptionResolver<Void, NullPointerException>() {
			@Override
			public Void onCatch(NullPointerException exception) {
				exception.printStackTrace();
				return null;
			}
		}).exception(new ExceptionResolver<Void, TimeoutException>() {
			@Override
			public Void onCatch(TimeoutException exception) {
				exception.printStackTrace();
				return null;
			}
		});

		new Thread() {
			public void run() {
				try {
					Thread.sleep(5000);
				} catch (InterruptedException e) {
					defer.reject(e);
				}
				defer.reject(new TimeoutException("defer timeout"));
			}
		}.start();


		Thenable<Integer> th = p1;

		Thenable<Integer> th2 = th.then(new SimpleResolver<Number, Integer>() {
			@Override
			public Integer resolve(Number newValue) {
				return 4;
			}
		});

		Thenable<Number> th3 = th2.cast();
		th3.then(new SimpleResolver<Number, String>() {
			@Override
			public String resolve(Number newValue) {
				System.out.println(newValue);
				return String.valueOf(newValue);
			}
		}).then(defer2);

		PromiseFactory.create(new DirectFunction<String>() {
			@Override
			public void run(Locker<String> locker) {
				locker.resolve("444");
			}
		}).make().then(defer2);

		Promise<Integer> intPromise = Promise.resolve(5);
		Promise<Integer> exPromise = Promise.reject(new Exception());
		Promise<Integer> clonePromise = Promise.resolve(th);

		Promise.all(intPromise, exPromise, clonePromise);


	}

}

Promise Static Method

• Promise.make is a promise factory method which can make a new promise
• Promise.all equals to javascript Promise.all
• Promise.race equals to javascript Promise.race
• Promise.series means running functions sequentially
• Promise.resolve equals to javascript Promise.resolve
• Promise.reject equals to javascript Promise.reject
• Promise.newException is to wrap and convert any exception into an internal runtime exception
• Promise.timeout is to make an n milli-seconds timeout promise

Promise Instance Method

• promise.then equals to javascript promise.then, we can resolve async/synchronized
• promise.getThen can make a new DirectFunction for making a new android promise
• promise.exception equals to javascript promise.catch
• promise.finalResult equals to javascript promise.done
• promise.cast can safely casting a Promise to a NEW Promise

Promise Resolver Types

in javascript, calling then method is as simple as promise.then(resolve, reject) in java, it's not easy to generate two object-arguments, so let's make it simple, that we can call .then like this promise.then(resolver) within which the resolver implements two method resolve and reject The Promise lib provides many pre-built resolvers, and all are based on DirectResolver or PromiseResolver. The former returns a result directly while the latter returns a promise

• DirectResolver turns a result into a new one
• PromiseResolver turns a result into a promise
• SimpleResolver and SimplePromiseResolver only care about resolving the result, other than popping exceptions on rejecting
• ExceptionResolver and ExceptionPromiseResolver only focus on a specific type of exception
• FinalResolver only processes the final stuff whenever it is resolved or rejected
• DoneResolver only processes the final stuff with two arguments: exception and result
• Deferred a specific resolver which will deliver the result to another deferred callback

PromiseDeferred Static Method

• PromiseDeferred.make is a factory method which can make a deferred object extending from Promise.Locker who is also a specific resolver

PromiseDeferred Instance Method

• resolve equals to javascript defer.resolve, usually used as a locker in promise
• reject equals to javascript defer.reject, usually used as a locker in promise
• done detect whether this deferred has been ever invoked resolve or reject
• post equals to android handler.post, using the internal handler
• postDelay equals to android handler.postDelay, using the internal handler
• removeCallbacks equals to android 'handler.removeCallbacks', using the internal handler
• promise equals to javascript defer.promise, which will generate a promise object who is waiting for the deferred to be resolved

PromiseFactory Static Method

• PromiseFactory.create will make a promise factory with a DirectFunction to implement

PromiseFactory Instance Method

• promiseFactory.run is a function you should override when you create your own factory unless you use static create
• promiseFactory.make is to make a new promise, each time you call this, the run(locker) will be executed

License

Copyright 2016 tangye1234.

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.