Add docs and examples for RS fromPublisher #25468

akka-docs/src/test/scala-jdk9-only/docs/stream/operators/source/FromPublisher.scala

@@ -0,0 +1,34 @@
+/*
+ * Copyright (C) 2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.source;
+
+//#imports
+import java.util.concurrent.Flow.Subscriber;
+import java.util.concurrent.Flow.Publisher;
+
+import akka.NotUsed;
+import akka.stream.scaladsl.Source;
+import akka.stream.scaladsl.JavaFlowSupport;
+
+//#imports
+
+object FromPublisher {
+    case class Row(name: String)
+
+    class DatabaseClient {
+        def fetchRows(): Publisher[Row] = ???
+    }
+
+    val databaseClient: DatabaseClient = ???
+
+    // #example
+    val names: Source[String, NotUsed] =
+      // A new subscriber will subscribe to the supplied publisher for each
+      // materialization, so depending on whether the database client supports
+      // this the Source can be materialized more than once.
+      JavaFlowSupport.Source.fromPublisher(databaseClient.fetchRows())
+        .map(row => row.name);
+    //#example
+}