Add more convenient version of CompletableFuture.allOf()

Change-Id: I40a2db5de22870adf524a9d0e1895c721291a50f

@@ -49,6 +49,7 @@ import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
 import java.util.function.Function;
 import java.util.function.Supplier;
+import java.util.stream.Collectors;
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
@@ -532,6 +533,22 @@ public abstract class Tools {
     }
 
     /**
+     * Returns a new CompletableFuture completed with a list of computed values
+     * when all of the given CompletableFuture complete.
+     *
+     * @param futures the CompletableFutures
+     * @param <T> value type of CompletableFuture
+     * @return a new CompletableFuture that is completed when all of the given CompletableFutures complete
+     */
+    public static <T> CompletableFuture<List<T>> allOf(List<CompletableFuture<T>> futures) {
+        return CompletableFuture.allOf(futures.toArray(new CompletableFuture[futures.size()]))
+                .thenApply(v -> futures.stream()
+                                .map(CompletableFuture::join)
+                                .collect(Collectors.toList())
+                );
+    }
+
+    /**
      * Returns the contents of {@code ByteBuffer} as byte array.
      * <p>
      * WARNING: There is a performance cost due to array copy