Making Embedder available to the application

First thing, we need to make the Embedder available to our application by adding a dependency on it in the pom.xml. Follow snippet shows the relevant <dependency> section of the application project's pom.xml.

<project>
  ...
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.codehaus.plexus</groupId>
      <artifactId>plexus-website-monitor-component</artifactId>
      <version>1.0-SNAPSHOT</version>
    </dependency>    
    <!-- Dependency to fetch Plexus Container implementation -->
    <dependency>
      <groupId>org.codehaus.plexus</groupId>
      <artifactId>plexus-container-default</artifactId>
      <version>1.0-alpha-9</version>     
    </dependency>
  </dependencies>
  ...
</project>

Regenerate the IDE project again as discussed in the previous section.

Starting up an embedded Plexus Container instance

Lets add some code to our Site Monitor application entry class that:

1. creates and starts an Embedder instance
2. Obtains PlexusContainer instance, and
3. performs a lookup for WebsiteMonitor component

   Our updated code looks as below:

   public class Main
   {
   
       /**
        * @param args
        */
       public static void main( String[] args )
       {
           Embedder embedder = new Embedder();
           try
           {
               embedder.start();
               PlexusContainer container = embedder.getContainer();
               WebsiteMonitor monitor = (WebsiteMonitor) container.lookup( WebsiteMonitor.ROLE );
               try
               {
                   monitor.monitor();
               }
               catch ( Exception e )
               {             
                   e.printStackTrace();
               }
   
           }
           catch ( PlexusContainerException e )
           {
               e.printStackTrace();
           }
           catch ( ComponentLookupException e )
           {
               e.printStackTrace();
           }
   
       }
   
   }

   At this point you can try running the above Main class from your favorite IDE. For demonstration purposes the WebsiteMonitor is by default configured to monitor http://plexus.codehaus.org. You should see it output the HTTP status for the monitoring request issued.

   Something like this:

   [INFO] HTTP request returned HTTP status code: 200 for website: http://plexus.codehaus.org/

How does Plexus Embedder works?

Plexus Embedder creates an instance of Plexus Container, which then loads and parses all available dependencies to discover any Plexus Components and registers them internally to make them available for look-ups.

To recapture again, the container looks for a Component descriptor under:

1. META-INF/plexus/components.xml

   This is exactly what those few lines of code achieve in the above snippet. You can, of course, use the Embedder to do fancier stuff.

   Great! we have just finished integrating our site monitor component into our site monitor application.