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JDeferred

Java Deferred / Promise library

JDeferred

JDeferred is a Java Deferred/Promise library similar to JQuery's Deferred Object.

Inspired by JQuery and Android Deferred Object.

Features

Maven

<dependency>
    <groupId>org.jdeferred</groupId>
    <artifactId>jdeferred-core</artifactId>
    <version>${version}</version>
</dependency>

Find available versions on Maven Central Repository.

Quick Examples

Deferred object and Promise

Deferred deferred = new DeferredObject();
Promise promise = deferred.promise();
promise.done(new DoneCallback() {
  public void onDone(Object result) {
    ...
  }
}).fail(new FailCallback() {
  public void onFail(Object rejection) {
    ...
  }
}).progress(new ProgressCallback() {
  public void onProgress(Object progress) {
    ...
  }
}).always(new AlwaysCallback() {
  public void onAlways(State state, Object result, Object rejection) {
    ...
  }
});

With the reference to deferred object, you can then trigger actions/updates:

deferred.resolve("done");
deferred.reject("oops");
deferred.progress("100%");

Filter

Deferred d = ;
Promise p = d.promise();
Promise filtered = p.then(new DoneFilter<Integer, Integer>() {
  public Integer filterDone(Integer result) P
    return result * 10;
  }
});

filtered.done(new DoneCallback<Integer>{
  public void onDone(Integer result) {
    // result would be original * 10
    System.out.println(result);
  }
});

d.resolve(3) -> 30.

Pipe

Since 1.1.0-Beta1

Deferred d = ...;
Promise p = d.promise();

p.then(new DonePipe<Integer, Integer, Exception, Void>() {
  public Deferred<Integer, Exception, Void> pipeDone(Integer result) {
    if (result < 100) {
      return new DeferredObject<Integer, Void, Void>().resolve(result);
    } else {
      return new DeferredObject<Integer, Void, Void>().reject(new Exception(...));
    }
  }
}).done(...).fail(...);

d.resolve(80) -> done!
d.resolve(100) -> fail!

Deferred Manager

DeferredManager dm = new DefaultDeferredManager();
Promise p1, p2, p3;
// initialize p1, p2, p3
dm.when(p1, p2, p3)
  .done()
  .fail()

You can also specify a Executor Service for your need.

DeferredManager dm = new DefaultDeferredManager(myExecutorService);

Runnable and Callable

You can use Callable and Runnable almost like a Promise without any additional work.

DeferredManager dm = new DefaultDeferredManager();
dm.when(new Callable<Integer>(){
  public Integer call() {
    // return something
    // or throw a new exception
  }
}).done(new DoneCallback<Integer>() {
  public void onDone(Integer result) {
    ...
  }
}).fail(new FailCallback<Throwable>() {
  public void onFail(Throwable e) {
    ...
  }
});

If you need to notify progress within your Callable or Runnable, you either need to create your own Deferred object and Promise, or you can use DeferredCallable and DeferredRunnable.

Use your own Deferred object

final Deferred deferred = ...
Promise promise = deferred.promise();
promise.then();
Runnable r = new Runnable() {
  public void run() {
    while () {
      deferred.notify(myProgress);
    }
    deferred.resolve("done");
  }
}

Or, extending DeferredRunnable

DeferredManager dm = ;
dm.when(new DeferredRunnable<Double>(){
  public void run() {
    while () {
      notify(myProgress);
    }
  }
}).then();

Wait and WaitSafely

Since 1.0.1

Normally, when using this framework, you would want to do things asynchronously. However, if there is a need to wait for all deferred tasks to finish, you can use Object.wait or Promise.waitSafely methods.

Promise p = dm.when(...)
  .done(...)
  .fail(...)

synchronized (p)
  while (p.isPending()) {
    try {
      p.wait();
    } catch (InterruptedException e) { ... }
  }
}

Alternatively, you can use a more simplified shortcut

Promise p = dm.when(...)
  .done(...)
  .fail(...)

try {
  p.waitSafely();
} catch (InterruptedException e) {
  ... 
}

Android Support

Since 1.1.0-Beta1

jdeferred-android is now available, and it can be included just like any other Android libraries! It also uses Android Maven pugin and builts apklib file. If you use Android Maven plugin, you can include dependency:

APKLIB:

<dependency>
  <groupId>org.jdeferred</groupId>
  <artifactId>jdeferred-android</artifactId>
  <version>...</version>
  <type>apklib</type>
</dependency>

AAR:

Since 1.2.0-Beta1

<dependency>
  <groupId>org.jdeferred</groupId>
  <artifactId>jdeferred-android-aar</artifactId>
  <version>...</version>
  <type>aar</type>
</dependency>

jdeferred-android introduces a new DeferredManager implementation called AndroidDeferredManager. AndroidDeferredManager makes sure that callbacks are executed in UI Thread rather than background Thread in order for callbacks to make UI updates. Alternatively, callbacks can also implement AndroidExecutionScopeable interface to fine-grain control whether the callback should execute in UI Thread or background Thread.

AndroidDeferredManager also supports new DeferredAsyncTask object. This object is based on Android's AsyncTask.

If you need to always execute callbacks in background thread, then you can continue to use DefaultDeferredManager.

Lastly, because JDeferred use SLF4J - you can further route log messages using slf4j-android.

Asynchronous Servlet

Here is a sample code on how to use JDeferred with Asynchronous Servlet!

@WebServlet(value = "/AsyncServlet", asyncSupported = true)
public class AsyncServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;
  private ExecutorService executorService = Executors.newCachedThreadPool();
  private DeferredManager dm = new DefaultDeferredManager(executorService);

  protected void doGet(HttpServletRequest request,
                       HttpServletResponse response) throws ServletException, IOException {
    final AsyncContext actx = request.startAsync(request, response);

    dm.when(new Callable<String>() {
      @Override
      public String call() throws Exception {
        if (actx.getRequest().getParameter("fail") != null) {
          throw new Exception("oops!");
        }
        Thread.sleep(2000);
        return "Hello World!";
      }
    }).then(new DoneCallback<String>() {
      @Override
      public void onDone(String result) {
        actx.getRequest().setAttribute("message", result);
        actx.dispatch("/hello.jsp");
      }
    }).fail(new FailCallback<Throwable>() {
      @Override
      public void onFail(Throwable exception) {
        actx.getRequest().setAttribute("exception", exception);
        actx.dispatch("/error.jsp");
      }
    });
  }
}

Java 8 Lambda

Now this is pretty cool when used with Java 8 Lambda!

dm.when(() -> {
  return "Hey!";
}).done(r -> System.out.println(r));

dm.when(
  () -> { return "Hello"; },
  () -> { return "World"; }
).done(rs ->
  rs.forEach(r -> System.out.println(r.getResult()))
);