Promise Map

promiseDeferred.java

/** the original Deferred (similar to jQuery) based implementation with lots of mutation */
public Promise<MyData> getMyDataAsync(String id) {
  // create a new Deferred instance to represent this operation
  final Deferred<MyData> deferred = Deferred.create();
  // perform an async operation to get mydata, typically with a lower-level async api
  rawDataClient.get(id)
    // handle success case
    .done(new Effect<Map<String, Object>>() {
      public void handle(Map<String, Object> value) {
        // convert the result into the target type and resolve the deferred
        deferred.resolve(myDataFromRawData(value));
      }
   })
    // use Promises.reject to forward failures to this higher-level deferred
    .fail(reject(deferred));
  // return the deferred's promise
  return deferred.promise();
}

promiseExample.java

/** alternate version using Promise.map */
public Promise<MyData> getMyDataAsync(String id) {
  // perform an async operation to get mydata, typically with a lower-level async api
  return rawDataClient.get(id)
    .map(new Function<Map<String, Object>, MyData>() {
      public MyData apply(Map<String, Object> value) {
        // convert the result into the target type
        return myDataFromRawData(value);
      }
  };
}

/** composing multiple async ops with flatMap */
public Promise<MoreData> getMoreDataAsync(String id) {
  // perform an async operation to get mydata, typically with a lower-level async api
  return rawDataClient.get(id)
    .flatMap(new Function<Map<String, Object>, Promise<MoreData>>() {
      public Promise<MyData> apply(Map<String, Object> value) {
        // make a further async call
        return rawDataClient.getFromMyData(myDataFromRawData(value));
      }
  };
}

promiseExample.scala

// the same as above (almost to the bytecode), but expressed in Scala:

def getMyDataAsync(id: String) =
  // perform an async operation to get mydata, typically with a lower-level async api
  rawDataClient.get(id).map { myDataFromRawData }

def getMoreDataAsync(id: String) =
  rawDataClient.get(id).flatMap {
    value => rawDataClient.getFromMyData(myDataFromRawData(value));
  }