diff --git a/http-core/src/main/java/org/apache/pekko/http/javadsl/model/MediaTypes.java b/http-core/src/main/java/org/apache/pekko/http/javadsl/model/MediaTypes.java
index dcae80ca8..ae1f0c7b8 100644
--- a/http-core/src/main/java/org/apache/pekko/http/javadsl/model/MediaTypes.java
+++ b/http-core/src/main/java/org/apache/pekko/http/javadsl/model/MediaTypes.java
@@ -467,7 +467,7 @@ public static MediaType.Binary applicationBinary(
             : org.apache.pekko.http.scaladsl.model.MediaType.NotCompressible$.MODULE$;
 
     scala.collection.immutable.Seq<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions));
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions));
 
     return org.apache.pekko.http.scaladsl.model.MediaType.applicationBinary(subType, comp, fileEx);
   }
@@ -478,7 +478,7 @@ public static MediaType.Binary applicationBinary(
         (org.apache.pekko.http.scaladsl.model.MediaType.Compressibility) compressibility;
 
     scala.collection.immutable.Seq<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions));
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions));
 
     return org.apache.pekko.http.scaladsl.model.MediaType.applicationBinary(subType, comp, fileEx);
   }
@@ -489,7 +489,7 @@ public static MediaType.WithFixedCharset applicationWithFixedCharset(
         (org.apache.pekko.http.scaladsl.model.HttpCharset) charset;
 
     scala.collection.immutable.Seq<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions));
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions));
 
     return org.apache.pekko.http.scaladsl.model.MediaType.applicationWithFixedCharset(
         subType, cs, fileEx);
@@ -498,7 +498,7 @@ public static MediaType.WithFixedCharset applicationWithFixedCharset(
   public static MediaType.WithOpenCharset applicationWithOpenCharset(
       String subType, String... fileExtensions) {
     scala.collection.immutable.Seq<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions));
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions));
 
     return org.apache.pekko.http.scaladsl.model.MediaType.applicationWithOpenCharset(
         subType, fileEx);
@@ -512,7 +512,7 @@ public static MediaType.Binary audio(
             : org.apache.pekko.http.scaladsl.model.MediaType.NotCompressible$.MODULE$;
 
     scala.collection.immutable.Seq<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions));
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions));
 
     return org.apache.pekko.http.scaladsl.model.MediaType.audio(subType, comp, fileEx);
   }
@@ -523,7 +523,7 @@ public static MediaType.Binary audio(
         (org.apache.pekko.http.scaladsl.model.MediaType.Compressibility) compressibility;
 
     scala.collection.immutable.Seq<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions));
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions));
 
     return org.apache.pekko.http.scaladsl.model.MediaType.audio(subType, comp, fileEx);
   }
@@ -536,7 +536,7 @@ public static MediaType.Binary image(
             : org.apache.pekko.http.scaladsl.model.MediaType.NotCompressible$.MODULE$;
 
     scala.collection.immutable.Seq<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions));
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions));
 
     return org.apache.pekko.http.scaladsl.model.MediaType.image(subType, comp, fileEx);
   }
@@ -547,7 +547,7 @@ public static MediaType.Binary image(
         (org.apache.pekko.http.scaladsl.model.MediaType.Compressibility) compressibility;
 
     scala.collection.immutable.Seq<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions));
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions));
 
     return org.apache.pekko.http.scaladsl.model.MediaType.image(subType, comp, fileEx);
   }
@@ -560,7 +560,7 @@ public static MediaType.Binary message(
             : org.apache.pekko.http.scaladsl.model.MediaType.NotCompressible$.MODULE$;
 
     scala.collection.immutable.Seq<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions));
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions));
 
     return org.apache.pekko.http.scaladsl.model.MediaType.message(subType, comp, fileEx);
   }
@@ -571,14 +571,14 @@ public static MediaType.Binary message(
         (org.apache.pekko.http.scaladsl.model.MediaType.Compressibility) compressibility;
 
     scala.collection.immutable.Seq<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions));
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions));
 
     return org.apache.pekko.http.scaladsl.model.MediaType.message(subType, comp, fileEx);
   }
 
   public static MediaType.WithOpenCharset text(String subType, String... fileExtensions) {
     scala.collection.immutable.Seq<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions));
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions));
 
     return org.apache.pekko.http.scaladsl.model.MediaType.text(subType, fileEx);
   }
@@ -591,7 +591,7 @@ public static MediaType.Binary video(
             : org.apache.pekko.http.scaladsl.model.MediaType.NotCompressible$.MODULE$;
 
     scala.collection.immutable.Seq<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions));
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions));
 
     return org.apache.pekko.http.scaladsl.model.MediaType.video(subType, comp, fileEx);
   }
@@ -602,7 +602,7 @@ public static MediaType.Binary video(
         (org.apache.pekko.http.scaladsl.model.MediaType.Compressibility) compressibility;
 
     scala.collection.immutable.Seq<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions));
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions));
 
     return org.apache.pekko.http.scaladsl.model.MediaType.video(subType, comp, fileEx);
   }
@@ -638,8 +638,7 @@ public static MediaType.Binary customBinary(
             : org.apache.pekko.http.scaladsl.model.MediaType.NotCompressible$.MODULE$;
 
     scala.collection.immutable.List<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions))
-            .toList();
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions)).toList();
 
     scala.collection.immutable.Map<String, String> p = Util.convertMapToScala(params);
 
@@ -658,8 +657,7 @@ public static MediaType.Binary customBinary(
         (org.apache.pekko.http.scaladsl.model.MediaType.Compressibility) compressibility;
 
     scala.collection.immutable.List<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions))
-            .toList();
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions)).toList();
 
     scala.collection.immutable.Map<String, String> p = Util.convertMapToScala(params);
 
@@ -678,8 +676,7 @@ public static MediaType.WithFixedCharset customWithFixedCharset(
         (org.apache.pekko.http.scaladsl.model.HttpCharset) charset;
 
     scala.collection.immutable.List<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions))
-            .toList();
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions)).toList();
 
     scala.collection.immutable.Map<String, String> p = Util.convertMapToScala(params);
 
@@ -694,8 +691,7 @@ public static MediaType.WithOpenCharset customWithOpenCharset(
       boolean allowArbitrarySubtypes,
       String... fileExtensions) {
     scala.collection.immutable.List<String> fileEx =
-        org.apache.pekko.japi.Util.<String>immutableSeq(java.util.Arrays.asList(fileExtensions))
-            .toList();
+        Util.<String, String>convertIterable(java.util.Arrays.asList(fileExtensions)).toList();
 
     scala.collection.immutable.Map<String, String> p = Util.convertMapToScala(params);
 
diff --git a/http-core/src/main/scala/org/apache/pekko/http/javadsl/ConnectionContext.scala b/http-core/src/main/scala/org/apache/pekko/http/javadsl/ConnectionContext.scala
index 61e6010d6..5124ee194 100644
--- a/http-core/src/main/scala/org/apache/pekko/http/javadsl/ConnectionContext.scala
+++ b/http-core/src/main/scala/org/apache/pekko/http/javadsl/ConnectionContext.scala
@@ -17,8 +17,8 @@ import java.util.{ Collection => JCollection, Optional }
 
 import org.apache.pekko
 import pekko.annotation.{ ApiMayChange, DoNotInherit }
+import pekko.http.impl.util.Util
 import pekko.http.scaladsl
-import pekko.japi.Util
 import pekko.stream.TLSClientAuth
 import pekko.util.OptionConverters._
 import com.typesafe.sslconfig.pekko.PekkoSSLConfig
@@ -80,8 +80,8 @@ object ConnectionContext {
     scaladsl.ConnectionContext.https(
       sslContext,
       sslConfig.toScala,
-      enabledCipherSuites.toScala.map(Util.immutableSeq(_)),
-      enabledProtocols.toScala.map(Util.immutableSeq(_)),
+      enabledCipherSuites.toScala.map(Util.convertIterable[String, String](_)),
+      enabledProtocols.toScala.map(Util.convertIterable[String, String](_)),
       clientAuth.toScala,
       sslParameters.toScala)
 
@@ -97,8 +97,8 @@ object ConnectionContext {
     scaladsl.ConnectionContext.https(
       sslContext,
       None,
-      enabledCipherSuites.toScala.map(Util.immutableSeq(_)),
-      enabledProtocols.toScala.map(Util.immutableSeq(_)),
+      enabledCipherSuites.toScala.map(Util.convertIterable[String, String](_)),
+      enabledProtocols.toScala.map(Util.convertIterable[String, String](_)),
       clientAuth.toScala,
       sslParameters.toScala)
 
diff --git a/http/src/main/scala/org/apache/pekko/http/javadsl/server/Rejections.scala b/http/src/main/scala/org/apache/pekko/http/javadsl/server/Rejections.scala
index c1864701a..7580861aa 100644
--- a/http/src/main/scala/org/apache/pekko/http/javadsl/server/Rejections.scala
+++ b/http/src/main/scala/org/apache/pekko/http/javadsl/server/Rejections.scala
@@ -25,7 +25,7 @@ import java.lang.{ Iterable => JIterable }
 
 import pekko.annotation.DoNotInherit
 import pekko.http.scaladsl
-import pekko.japi.Util
+import pekko.http.impl.util.Util
 import pekko.pattern.CircuitBreakerOpenException
 import pekko.util.OptionConverters._
 
@@ -416,7 +416,8 @@ object Rejections {
     s.UnsupportedRequestEncodingRejection(supported.asScala)
 
   def unsatisfiableRange(unsatisfiableRanges: java.lang.Iterable[ByteRange], actualEntityLength: Long) =
-    UnsatisfiableRangeRejection(Util.immutableSeq(unsatisfiableRanges).map(_.asScala), actualEntityLength)
+    UnsatisfiableRangeRejection(Util.convertIterable[ByteRange, ByteRange](unsatisfiableRanges).map(_.asScala),
+      actualEntityLength)
 
   def tooManyRanges(maxRanges: Int) = TooManyRangesRejection(maxRanges)
 
diff --git a/http/src/main/scala/org/apache/pekko/http/javadsl/server/RouteResult.scala b/http/src/main/scala/org/apache/pekko/http/javadsl/server/RouteResult.scala
index 2201d6ef2..757c0a0d5 100644
--- a/http/src/main/scala/org/apache/pekko/http/javadsl/server/RouteResult.scala
+++ b/http/src/main/scala/org/apache/pekko/http/javadsl/server/RouteResult.scala
@@ -28,8 +28,7 @@ trait Rejected extends RouteResult {
 
 object RouteResults {
   import pekko.http.scaladsl.{ server => s }
-  import pekko.japi.Util
-  import pekko.http.impl.util.JavaMapping
+  import pekko.http.impl.util.{ JavaMapping, Util }
   import JavaMapping.Implicits._
   import RoutingJavaMapping._
 
@@ -38,7 +37,7 @@ object RouteResults {
   }
 
   def rejected(rejections: java.lang.Iterable[Rejection]): Rejected = {
-    s.RouteResult.Rejected(Util.immutableSeq(rejections).map(_.asScala))
+    s.RouteResult.Rejected(Util.convertIterable[Rejection, Rejection](rejections).map(_.asScala))
   }
 
 }
diff --git a/http/src/main/scala/org/apache/pekko/http/javadsl/server/directives/BasicDirectives.scala b/http/src/main/scala/org/apache/pekko/http/javadsl/server/directives/BasicDirectives.scala
index 2af03fedb..72605e383 100644
--- a/http/src/main/scala/org/apache/pekko/http/javadsl/server/directives/BasicDirectives.scala
+++ b/http/src/main/scala/org/apache/pekko/http/javadsl/server/directives/BasicDirectives.scala
@@ -17,39 +17,36 @@ import java.util.function.{ Function => JFunction }
 
 import org.apache.pekko
 import pekko.actor.ActorSystem
-import pekko.http.impl.util.JavaMapping
-import pekko.http.javadsl.settings.ParserSettings
-import pekko.http.javadsl.settings.RoutingSettings
+import pekko.dispatch.ExecutionContexts
+import pekko.event.LoggingAdapter
 import pekko.japi.Util
+import pekko.stream.Materializer
 import pekko.stream.javadsl.Source
 import pekko.util.ByteString
+import pekko.util.FutureConverters._
 
-import scala.concurrent.ExecutionContextExecutor
 import pekko.http.impl.model.JavaUri
-import pekko.http.javadsl.model.HttpRequest
-import pekko.http.javadsl.model.HttpEntity
-import pekko.http.javadsl.model.RequestEntity
-import pekko.http.javadsl.model.Uri
+import pekko.http.impl.util.JavaMapping
+import pekko.http.impl.util.Util.convertIterable
+import pekko.http.javadsl.model.{ HttpEntity, HttpRequest, RequestEntity, Uri }
 import pekko.http.javadsl.server._
-import pekko.http.scaladsl.server.{ Directives => D }
+import pekko.http.javadsl.settings.{ ParserSettings, RoutingSettings }
 import pekko.http.scaladsl
-import pekko.stream.Materializer
-import java.util.function.Supplier
-import java.util.{ List => JList }
+import pekko.http.scaladsl.server.{ Directives => D }
 
 import pekko.http.javadsl.model.HttpResponse
 import pekko.http.javadsl.model.ResponseEntity
 import pekko.http.javadsl.model.HttpHeader
 import pekko.http.scaladsl.util.FastFuture._
+import pekko.http.javadsl.server
+
 import java.lang.{ Iterable => JIterable }
+import java.util.function.Supplier
+import java.util.{ List => JList }
 import java.util.concurrent.CompletionStage
 import java.util.function.Predicate
 
-import pekko.dispatch.ExecutionContexts
-import pekko.event.LoggingAdapter
-import pekko.http.javadsl.server
-import pekko.util.FutureConverters._
-
+import scala.concurrent.ExecutionContextExecutor
 import scala.concurrent.duration.FiniteDuration
 
 abstract class BasicDirectives {
@@ -66,7 +63,8 @@ abstract class BasicDirectives {
 
   def mapRejections(f: JFunction[JList[Rejection], JList[Rejection]], inner: Supplier[Route]): Route = RouteAdapter {
     D.mapRejections(rejections =>
-      Util.immutableSeq(f.apply(Util.javaArrayList(rejections.map(_.asJava)))).map(_.asScala)) { inner.get.delegate }
+      convertIterable[Rejection, Rejection](f.apply(Util.javaArrayList(rejections.map(_.asJava)))).map(
+        _.asScala)) { inner.get.delegate }
   }
 
   def mapResponse(f: JFunction[HttpResponse, HttpResponse], inner: Supplier[Route]): Route = RouteAdapter {
@@ -79,7 +77,10 @@ abstract class BasicDirectives {
 
   def mapResponseHeaders(f: JFunction[JList[HttpHeader], JList[HttpHeader]], inner: Supplier[Route]): Route =
     RouteAdapter {
-      D.mapResponseHeaders(l => Util.immutableSeq(f.apply(Util.javaArrayList(l))).map(_.asScala)) { inner.get.delegate } // TODO try to remove map()
+      D.mapResponseHeaders(l =>
+        convertIterable[HttpHeader, HttpHeader](f.apply(Util.javaArrayList(l))).map(_.asScala)) {
+        inner.get.delegate
+      } // TODO try to remove map()
     }
 
   def mapInnerRoute(f: JFunction[Route, Route], inner: Supplier[Route]): Route = RouteAdapter {
@@ -155,7 +156,7 @@ abstract class BasicDirectives {
    * to the list of rejections potentially coming back from the inner route.
    */
   def cancelRejections(classes: JIterable[Class[_]], inner: Supplier[Route]): Route = RouteAdapter {
-    D.cancelRejections(Util.immutableSeq(classes): _*) { inner.get.delegate }
+    D.cancelRejections(convertIterable[Class[_], Class[_]](classes): _*) { inner.get.delegate }
   }
 
   /**
diff --git a/http/src/main/scala/org/apache/pekko/http/scaladsl/server/Rejection.scala b/http/src/main/scala/org/apache/pekko/http/scaladsl/server/Rejection.scala
index 21e4cfd8e..37a1c74e1 100644
--- a/http/src/main/scala/org/apache/pekko/http/scaladsl/server/Rejection.scala
+++ b/http/src/main/scala/org/apache/pekko/http/scaladsl/server/Rejection.scala
@@ -18,7 +18,7 @@ import java.util.Optional
 import java.util.function.Function
 
 import org.apache.pekko
-import pekko.japi.Util
+import pekko.http.impl.util.Util
 import pekko.http.scaladsl.model._
 import pekko.http.scaladsl.model.headers.{ ByteRange, HttpChallenge, HttpEncoding }
 import pekko.http.javadsl.{ model, server => jserver }
@@ -335,7 +335,9 @@ final case class TransformationRejection(transform: immutable.Seq[Rejection] =>
     override def apply(t: Iterable[jserver.Rejection]): Iterable[jserver.Rejection] = {
       // explicit collects assignment is because of unidoc failing compilation on .asScala and .asJava here
       val transformed: Seq[jserver.Rejection] =
-        transform(Util.immutableSeq(t).collect { case r: Rejection => r }).collect { case j: jserver.Rejection => j }
+        transform(Util.convertIterable[jserver.Rejection, jserver.Rejection](t).collect { case r: Rejection =>
+          r
+        }).collect { case j: jserver.Rejection => j }
       transformed.asJava // TODO "asJavaDeep" and optimise?
     }
   }