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64 lines
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.. _http-javadsl-migration-guide:
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Migration Guide from "old" HTTP JavaDSL
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=======================================
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The so-called "old" JavaDSL for Akka HTTP was initially developed during the project's experimental phase,
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and thanks to multiple user comments and contributions we were able to come up with a more Java 8 "feel",
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which at the same time is also closer to the existing ScalaDSL.
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The previous DSL has been entirely removed and replaced with the the so-called "new" one.
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Upgrading to the new DSL is **highly encouraged** since the old one not only was rather hard to work with,
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it actually was not possible to express many typical use-cases using it.
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The most major changes include:
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HttpApp is gone
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---------------
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``HttpApp`` (a helper class containing a ``main()`` implementation) is gone, as we would like to encourage understanding
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how the various elements of the API fit together.
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Instead developers should start applications "manually", by converting a ``Route`` to a ``Flow<HttpRequest, HttpResponse, ?>``
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using the ``Route.flow`` method. For examples of full apps refer to :ref:`http-testkit-java`.
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``RequestVal`` is gone
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----------------------
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The old API heavily relied on the concept of "request values" which could be used to extract a value from a request context.
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Based on community feedback and our own experience we found them too hard to work with in more complex settings.
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The concept of a request value has been completely removed, and replaced with proper "directives", exacly like in the ScalaDSL.
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**Previously**::
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RequestVal<Host> host = Headers.byClass(Host.class).instance();
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final Route route =
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route(
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handleWith1(host, (ctx, h) ->
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ctx.complete(String.format("Host header was: %s", h.host()))
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)
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);
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**Now**::
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final Route route =
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headerValueByType(Host.class, host -> complete("Host was: " + host));
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All of ScalaDSL routing has corresponding JavaDSL
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-------------------------------------------------
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Both ``Route``, ``RouteResult`` and other important core concepts such as ``Rejections`` are now modeled 1:1 with Scala,
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making is much simpler to understand one API based on the other one – tremendously useful when learning about some nice
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pattern from blogs which used Scala, yet need to apply it in Java and the other way around.
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It is now possible to implement marshallers using Java. Refer to :ref:`marshalling-java` for details.
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Migration help
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--------------
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As always, feel free to reach out via the `akka-user <https://groups.google.com/forum/#!searchin/akka-user/>`_ mailing list or gitter channels,
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to seek help or guidance when migrating from the old APIs.
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For Lightbend subscription owners it is possible to reach out to the core team for help in the migration by asking specific
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questions via the `Lightbend customer portal <https://portal.lightbend.com/>`_.
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