119 lines
3.7 KiB
HTML
119 lines
3.7 KiB
HTML
<!-- <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>onReceive</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>
|