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+sam #13890 Add Akka Main Activator template for Java 8

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Björn Antonsson 2014-04-16 08:42:32 +02:00
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<!-- <html> -->
<head>
<title>The Obligatory Hello World</title>
</head>
<body>
<div>
<h2>The Obligatory Hello World</h2>
<p>
Since every programming paradigm needs to solve the tough problem of printing a
well-known greeting to the console we’ll introduce you to the actor-based
version.
</p>
<p>
Open <a href="#code/src/main/java/sample/hello/HelloWorld.java" class="shortcut">HelloWorld.java</a>
</p>
<p>
The <code>HelloWorld</code> actor is the application’s “main” class; when it terminates
the application will shut down—more on that later. The main business logic
happens in the <code>preStart</code> method, where a <code>Greeter</code> actor is created
and instructed to issue that greeting we crave for. When the greeter is done it
will tell us so by sending back a message, and when that message has been
received it will be passed into the behavior described by the <code>receive</code>
method where we can conclude the demonstration by stopping the <code>HelloWorld</code>
actor.
</p>
</div>
<div>
<h2>The Greeter</h2>
<p>
You will be very curious to see how the <code>Greeter</code> actor performs the
actual task. Open <a href="#code/src/main/java/sample/hello/Greeter.java" class="shortcut">Greeter.java</a>.
</p>
<p>
This is extremely simple now: after its creation this actor will not do
anything until someone sends it a message, and if that happens to be an
invitation to greet the world then the <code>Greeter</code> complies and informs the
requester that the deed has been done.
</p>
</div>
<div>
<h2>Main class</h2>
<p>
Go to the <a href="#run" class="shortcut">Run</a> tab, and start the application main class
<code>sample.hello.Main</code>. In the log output you can see the "Hello World!" greeting.
</p>
<p>
<a href="#code/src/main/java/sample/hello/Main.java" class="shortcut">Main.java</a>
is actually just a small wrapper around the generic launcher class <code>akka.Main</code>,
which expects only one argument: the class name of the application’s main actor. This main
method will then create the infrastructure needed for running the actors, start the
given main actor and arrange for the whole application to shut down once the
main actor terminates. Thus you will be able to run the application with a
command similar to the following:
</p>
<pre><code>
java -classpath <all those JARs> akka.Main sample.hello.HelloWorld
</code></pre>
<p>
This conveniently assumes placement of the above class definitions in package
<code>sample.hello</code> and it further assumes that you have the required JAR files for
<code>scala-library</code>, <code>typesafe-config</code> and <code>akka-actor</code> available.
The easiest would be to manage these dependencies with a
<a href="http://doc.akka.io/docs/akka/2.4-SNAPSHOT/intro/getting-started.html#Using_a_build_tool" target="_blank">build tool</a>.
</p>
<p>
If you need more control of the startup code than what is provided by <code>akka.Main</code>
you can easily write your own main class such as
<a href="#code/src/main/java/sample/hello/Main2.java" class="shortcut">Main2.java</a>
</p>
<p>
Try to run the <code>sample.hello.Main2</code> class
by selecting it in the 'Main class' menu in the <a href="#run" class="shortcut">Run</a> tab.
</p>
</div>
<div>
<h2>Run with Maven</h2>
<p>
This sample also includes a Maven <a href="#code/pom.xml" class="shortcut">pom.xml</a>.
</p>
<p>
You can run the main classes with <code>mvn</code> from a terminal window using the
<a href="http://mojo.codehaus.org/exec-maven-plugin/" target="_blank">Exec Maven Plugin</a>.
</p>
<pre><code>
mvn compile exec:java -Dexec.mainClass="akka.Main" -Dexec.args="sample.hello.HelloWorld"
</code></pre>
<pre><code>
mvn compile exec:java -Dexec.mainClass="sample.hello.Main2"
</code></pre>
</div>
</body>
</html>