+str #18565 termination notification combinator

akka-stream/src/main/scala/akka/stream/javadsl/Source.scala

@@ -13,7 +13,7 @@ import akka.event.LoggingAdapter
 import akka.japi.{ Pair, Util, function }
 import akka.stream.Attributes._
 import akka.stream._
-import akka.stream.impl.fusing.Delay
+import akka.stream.impl.fusing.{ GraphStages, Delay }
 import akka.stream.impl.{ ConstantFun, StreamLayout }
 import akka.stream.stage.Stage
 import akka.util.ByteString
@@ -1721,6 +1721,15 @@ final class Source[+Out, +Mat](delegate: scaladsl.Source[Out, Mat]) extends Grap
    */
   def detach: javadsl.Source[Out, Mat] = new Source(delegate.detach)
 
+  /**
+   * Materializes to `Future[Done]` that completes on getting termination message.
+   * The Future completes with success when received complete message from upstream or cancel
+   * from downstream. It fails with the same error when received error message from
+   * downstream.
+   */
+  def watchTermination[M]()(matF: function.Function2[Mat, Future[Done], M]): javadsl.Source[Out, M] =
+    new Source(delegate.watchTermination()(combinerToScala(matF)))
+
   /**
    * Delays the initial element by the specified duration.
    *