Creating toObservable for Future

rxjava-core/src/main/java/rx/observables/Observable.java

@@ -22,6 +22,7 @@
 import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.Future;
 
 import org.junit.Before;
 import org.junit.Test;
@@ -42,6 +43,7 @@
 import rx.observables.operations.OperationSkip;
 import rx.observables.operations.OperationSynchronize;
 import rx.observables.operations.OperationTake;
+import rx.observables.operations.OperationToObservableFuture;
 import rx.observables.operations.OperationToObservableIterable;
 import rx.observables.operations.OperationToObservableList;
 import rx.observables.operations.OperationToObservableSortedList;
@@ -1359,6 +1361,23 @@ public static <T> Observable<T> toObservable(Iterable<T> iterable) {
         return create(OperationToObservableIterable.toObservableIterable(iterable));
     }
 
+    /**
+     * Converts an Future to a Observable sequence.
+     * 
+     * Any object that supports the {@link Future} interface can be converted into a Observable that emits
+     * the return value of the get() method in the object, by passing the object into the <code>toObservable</code> method.
+     * 
+     * @param future
+     *            the source {@link Future}
+     * @param <T>
+     *            the type of of object that the future's returns and the type emitted by the resulting
+     *            Observable
+     * @return a Observable that emits the item from the source Future
+     */
+    public static <T> Observable<T> toObservable(Future<T> future) {
+        return create(OperationToObservableFuture.toObservableFuture(future));
+    }
+
     /**
      * Converts an Array sequence to a Observable sequence.
      * 

rxjava-core/src/main/java/rx/observables/operations/OperationToObservableFuture.java

@@ -0,0 +1,84 @@
+package rx.observables.operations;
+
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import java.util.concurrent.Future;
+
+import org.junit.Test;
+
+import rx.observables.Observable;
+import rx.observables.Observer;
+import rx.observables.Subscription;
+import rx.util.functions.Func1;
+
+public class OperationToObservableFuture {
+    private static class ToObservableFuture<T> implements OperatorSubscribeFunction<T> {
+        private final Future<T> that;
+
+        public ToObservableFuture(Future<T> that) {
+            this.that = that;
+        }
+
+        @Override
+        public Subscription call(Observer<T> observer) {
+            try {
+                T value = that.get();
+                if (!that.isCancelled()) {
+                    observer.onNext(value);
+                }
+                observer.onCompleted();
+            } catch (Exception e) {
+                observer.onError(e);
+            }
+
+            // the get() has already completed so there is no point in
+            // giving the user a way to cancel.
+            return Observable.noOpSubscription();
+        }
+    }
+
+    public static <T> Func1<Observer<T>, Subscription> toObservableFuture(final Future<T> that) {
+        return new ToObservableFuture<T>(that);
+    }
+
+    @SuppressWarnings("unchecked")
+    public static class UnitTest {
+        @Test
+        public void testSuccess() throws Exception {
+            Future<Object> future = mock(Future.class);
+            Object value = new Object();
+            when(future.get()).thenReturn(value);
+            ToObservableFuture ob = new ToObservableFuture(future);
+            Observer<Object> o = mock(Observer.class);
+
+            Subscription sub = ob.call(o);
+            sub.unsubscribe();
+
+            verify(o, times(1)).onNext(value);
+            verify(o, times(1)).onCompleted();
+            verify(o, never()).onError(null);
+            verify(future, never()).cancel(true);
+        }
+
+        @Test
+        public void testFailure() throws Exception {
+            Future<Object> future = mock(Future.class);
+            RuntimeException e = new RuntimeException();
+            when(future.get()).thenThrow(e);
+            ToObservableFuture ob = new ToObservableFuture(future);
+            Observer<Object> o = mock(Observer.class);
+
+            Subscription sub = ob.call(o);
+            sub.unsubscribe();
+
+            verify(o, never()).onNext(null);
+            verify(o, never()).onCompleted();
+            verify(o, times(1)).onError(e);
+            verify(future, never()).cancel(true);
+        }
+    }
+}