JBoss Microcontainer Sample Application – Howto

2012-12-16

JBoss Microcontainer Sample Application – Howto

A very brief intro to JBoss Microcontainer.

Prerequisites

This tutorial assumes you're familiar with Maven. If you're not, don't worry – most IDE's will hide it from you quite well.

You may also be familiar with Spring IoC, which is not only similar to, but compatible with JBoss Microcontainer.

Maven configuration

You need to set up Maven to use JBoss Maven repository (all JBoss projects use this repository, by the way). Follow instalation instructions in JBoss Micontainer User Guide. Here is the shortened version of the profile:

<profile>
  <id>jboss.repository</id>
    <activation> <property> <name>!jboss.repository.off</name> </property> </activation>
  <repositories>
    <repository> <id>snapshots.jboss.org</id> <url>http://snapshots.jboss.org/maven2</url> <snapshots> <enabled>true</enabled> </snapshots> </repository>
    <repository> <id>repository.jboss.org</id> <url>http://repository.jboss.org/maven2</url> <snapshots><enabled>false</enabled></snapshots> </repository>
  </repositories>
  <pluginRepositories>
    <pluginRepository> <id>repository.jboss.org</id> <url>http://repository.jboss.org/maven2</url> <snapshots><enabled>false</enabled></snapshots> </pluginRepository>
    <pluginRepository> <id>snapshots.jboss.org</id> <url>http://snapshots.jboss.org/maven2</url> <snapshots><enabled>true</enabled></snapshots> </pluginRepository>
  </pluginRepositories>
</profile>

Then add this dependency to your project:

<dependency>
  <groupId>org.jboss.microcontainer</groupId>
  <artifactId>jboss-kernel</artifactId>
  <version>2.0.9.GA</version>
</dependency>

Then clean and build the project – that will download all the dependencies (may take a while).

What is JBoss Microcontainer good for?

It's an inversion of control (IoC) framework, like Spring or Guice. IoC frameworks let you create, configure and wire up simple Java objects (POJOs). Classes of these objects need no special coding to be usable with JBoss Microcontainer. These objects usualy represent the modules of your application.

An example of how to use IoC in a typical web application

Create and configure a JDBC datasource
Create and configure a connection pool (C3P0), and attach 1) as it's datasource.
Create and configure Hibernate entity manager, and attach 2) as it's datasource.
Create and configure your controller, and „inject“ (== attach) 3) as it's EntityManagerFactory.

Creating a class to use with JBoss Microcontainer

As written above, any class can be used.

package cz.zizka.ondra.jbmctest;

public class Car
{

  private String name;
  public String getName() {    return name;  }
  public void setName( String name ) {    this.name = name;  }

  public int litresOfFuel;
  public int getLitresOfFuel() {    return litresOfFuel;  }
  public void setLitresOfFuel( int litresOfFuel ) {    this.litresOfFuel = litresOfFuel;  }


  public Car(){}

  public Car( String name, int litres ){
    this.name = name;
    this.litresOfFuel = litres;
  }

  public String toString(){  return "Car \""+this.name+"\"";  }

}

Instantiating a class in JBoss Microcontainer

Create a XML file named jboss-beans.xml and put it to the resources dir (Maven's default is src/main/resources).

<?xml version="1.0" encoding="UTF-8"?>
<deployment xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="urn:jboss:bean-deployer:2.0 bean-deployer_2_0.xsd"
            xmlns="urn:jboss:bean-deployer:2.0">

   <bean name="myCar" class="cz.zizka.ondra.jbmctest.Car">
     <property name="name">Red Devil</property>
     <property name="litresOfFuel">37</property>
   </bean>

</deployment>

The example above calls a default constructor (with no arguments), and then sets the properties. If they were private and you had setters for them, those would be used.

An alternative way is to call the constructor:

<bean name="myCar" class="cz.zizka.ondra.jbmctest.Car">
 <constructor>
     <parameter>Red Devil</parameter>
     <parameter>37</parameter>
 </constructor>
</bean>

Wiring up the objects

To attach one object to the other, use <inject>:

package cz.zizka.ondra.jbmctest;

public class Garage
{
  private Car carInside;
  public Car getCarInside() {    return carInside;  }
  public void setCarInside( Car car ) {    this.carInside = car;  }

  public String toString(){
    return "Garage with a car: "+this.getCar();
  }
}

<?xml version="1.0" encoding="UTF-8"?>
<deployment xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="urn:jboss:bean-deployer:2.0 bean-deployer_2_0.xsd"
            xmlns="urn:jboss:bean-deployer:2.0">

   <bean name="myCar" class="cz.zizka.ondra.jbmctest.Car">
     <property name="name">Red Devil</property>
     <property name="litresOfFuel">37</property>
   </bean>

   <bean name="myGarage" class="cz.zizka.ondra.jbmctest.Garage">
     <property name="myGarage"><inject bean="myCar"/></property>
   </bean>

</deployment>

Creating JBoss Microcontainer object in your application (bootstraping)

public class App {

  public static void main( String[] args ) throws Throwable
  {

    // Bootstrap.
    BasicBootstrap bootstrap = new BasicBootstrap();
    bootstrap.run();


    // Load the bean definitions.
    ClassLoader cl = Thread.currentThread().getContextClassLoader();
    URL url = cl.getResource("jboss-beans.xml");
    BasicXMLDeployer deployer = new BasicXMLDeployer( bootstrap.getKernel() );
    deployer.deploy( url );

    // Get the garage bean.
    ControllerContext context = bootstrap.getKernel().getController().getInstalledContext("myGarage");
    System.out.println( "I have a garage: "+context.getTarget());

    // Clean up.
    deployer.shutdown();

  }// main()

}// class

JBoss Microcontainer Sample Application – Howto