Add a sample for Source.unfoldResource #25468

akka-docs/src/test/scala/docs/stream/operators/source/UnfoldResource.scala

@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2009-2019 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.source
+
+import akka.NotUsed
+import akka.actor.ActorSystem
+import akka.stream.scaladsl.Source
+
+object UnfoldResource {
+
+  // imaginary blocking API we need to use
+  // #unfoldResource-blocking-api
+  trait Database {
+    // blocking query
+    def doQuery(): QueryResult
+  }
+  trait QueryResult {
+    def hasMore: Boolean
+    // potentially blocking retrieval of each element
+    def nextEntry(): DatabaseEntry
+    def close(): Unit
+  }
+  trait DatabaseEntry
+  // #unfoldResource-blocking-api
+
+  def unfoldResourceExample(): Unit = {
+    implicit val actorSystem = ActorSystem()
+    // #unfoldResource
+    // we don't actually have one, it was just made up for the sample
+    val database: Database = ???
+
+    val queryResultSource: Source[DatabaseEntry, NotUsed] =
+      Source.unfoldResource[DatabaseEntry, QueryResult](
+        // open
+        { () =>
+          database.doQuery()
+        },
+        // read
+        { query =>
+          if (query.hasMore)
+            Some(query.nextEntry())
+          else
+            // signals end of resource
+            None
+        },
+        // close
+        query => query.close())
+
+    // process each element
+    queryResultSource.runForeach(println)
+    // #unfoldResource
+  }
+
+}