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158 lines
6.3 KiB
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.. _camel-scala:
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#######
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Camel
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#######
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Additional Resources
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====================
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For an introduction to akka-camel 2, see also the Peter Gabryanczyk's talk `Migrating akka-camel module to Akka 2.x`_.
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For an introduction to akka-camel 1, see also the `Appendix E - Akka and Camel`_
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(pdf) of the book `Camel in Action`_.
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.. _Appendix E - Akka and Camel: http://www.manning.com/ibsen/appEsample.pdf
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.. _Camel in Action: http://www.manning.com/ibsen/
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.. _Migrating akka-camel module to Akka 2.x: http://skillsmatter.com/podcast/scala/akka-2-x
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Other, more advanced external articles (for version 1) are:
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* `Akka Consumer Actors: New Features and Best Practices <http://krasserm.blogspot.com/2011/02/akka-consumer-actors-new-features-and.html>`_
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* `Akka Producer Actors: New Features and Best Practices <http://krasserm.blogspot.com/2011/02/akka-producer-actor-new-features-and.html>`_
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Introduction
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============
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The akka-camel module allows actors to receive
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and send messages over a great variety of protocols and APIs. This section gives
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a brief overview of the general ideas behind the akka-camel module, the
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remaining sections go into the details. In addition to the native Scala and Java
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actor API, actors can now exchange messages with other systems over large number
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of protocols and APIs such as HTTP, SOAP, TCP, FTP, SMTP or JMS, to mention a
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few. At the moment, approximately 80 protocols and APIs are supported.
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Apache Camel
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------------
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The akka-camel module is based on `Apache Camel`_, a powerful and light-weight
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integration framework for the JVM. For an introduction to Apache Camel you may
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want to read this `Apache Camel article`_. Camel comes with a
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large number of `components`_ that provide bindings to different protocols and
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APIs. The `camel-extra`_ project provides further components.
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.. _Apache Camel: http://camel.apache.org/
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.. _Apache Camel article: http://architects.dzone.com/articles/apache-camel-integration
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.. _components: http://camel.apache.org/components.html
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.. _camel-extra: http://code.google.com/p/camel-extra/
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Consumer
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--------
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Usage of Camel's integration components in Akka is essentially a
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one-liner. Here's an example.
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.. includecode:: code/akka/docs/camel/Introduction.scala#Consumer-mina
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The above example exposes an actor over a tcp endpoint on port 6200 via Apache
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Camel's `Mina component`_. The actor implements the endpointUri method to define
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an endpoint from which it can receive messages. After starting the actor, tcp
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clients can immediately send messages to and receive responses from that
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actor. If the message exchange should go over HTTP (via Camel's `Jetty
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component`_), only the actor's endpointUri method must be changed.
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.. _Mina component: http://camel.apache.org/mina.html
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.. _Jetty component: http://camel.apache.org/jetty.html
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.. includecode:: code/akka/docs/camel/Introduction.scala#Consumer
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Producer
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--------
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Actors can also trigger message exchanges with external systems i.e. produce to
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Camel endpoints.
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.. includecode:: code/akka/docs/camel/Introduction.scala
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:include: imports,Producer
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In the above example, any message sent to this actor will be sent to
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the JMS queue ``orders``. Producer actors may choose from the same set of Camel
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components as Consumer actors do.
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CamelMessage
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------------
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The number of Camel components is constantly increasing. The akka-camel module
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can support these in a plug-and-play manner. Just add them to your application's
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classpath, define a component-specific endpoint URI and use it to exchange
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messages over the component-specific protocols or APIs. This is possible because
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Camel components bind protocol-specific message formats to a Camel-specific
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`normalized message format`__. The normalized message format hides
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protocol-specific details from Akka and makes it therefore very easy to support
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a large number of protocols through a uniform Camel component interface. The
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akka-camel module further converts mutable Camel messages into immutable
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representations which are used by Consumer and Producer actors for pattern
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matching, transformation, serialization or storage.
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__ https://svn.apache.org/repos/asf/camel/trunk/camel-core/src/main/java/org/apache/camel/Message.java
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Dependencies
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============
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SBT
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---
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.. code-block:: scala
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"com.typesafe.akka" % "akka-camel" % "2.1-SNAPSHOT"
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Maven
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-----
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.. code-block:: xml
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<dependency>
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<groupId>com.typesafe.akka</groupId>
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<artifactId>akka-camel</artifactId>
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<version>2.1-SNAPSHOT</version>
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</dependency>
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.. _camel-consumer-actors:
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Consumer Actors
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================
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For objects to receive messages, they must mixin the `Consumer`_
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trait. For example, the following actor class (Consumer1) implements the
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endpointUri method, which is declared in the Consumer trait, in order to receive
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messages from the ``file:data/input/actor`` Camel endpoint.
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.. _Consumer: http://github.com/akka/akka/blob/master/akka-camel/src/main/scala/akka/camel/Consumer.scala
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.. includecode:: code/akka/docs/camel/Consumers.scala#Consumer1
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Whenever a file is put into the data/input/actor directory, its content is
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picked up by the Camel `file component`_ and sent as message to the
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actor. Messages consumed by actors from Camel endpoints are of type
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`CamelMessage`_. These are immutable representations of Camel messages.
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.. _file component: http://camel.apache.org/file2.html
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.. _Message: http://github.com/akka/akka/blob/master/akka-camel/src/main/scala/akka/camel/CamelMessage.scala
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Here's another example that sets the endpointUri to
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``jetty:http://localhost:8877/camel/default``. It causes Camel's `Jetty
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component`_ to start an embedded `Jetty`_ server, accepting HTTP connections
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from localhost on port 8877.
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.. _Jetty component: http://camel.apache.org/jetty.html
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.. _Jetty: http://www.eclipse.org/jetty/
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.. includecode:: code/akka/docs/camel/Consumers.scala#Consumer2
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After starting the actor, clients can send messages to that actor by POSTing to
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``http://localhost:8877/camel/default``. The actor sends a response by using the
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self.reply method (Scala). For returning a message body and headers to the HTTP
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client the response type should be `Message`_. For any other response type, a
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new Message object is created by akka-camel with the actor response as message
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body.
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.. _Message: http://github.com/akka/akka/blob/master/akka-camel/src/main/scala/akka/camel/CamelMessage.scala
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