[jboss-dev-forums] [Design the new POJO MicroContainer] - mc-script - and other stupid ideas

[adrian@jboss.org]

I got a bit bored yesterday so I decided to write an example that shows how
easy it is to extend the microctonainer's value system.
(Actually the example really shows off JBossXB's xml any handling).

By way of a stupid example, I decided to write a new ValueMetaData that
determines its values using the Java6 script engine stuff.
(As usual change svn to anonsvn if you don't have a jboss.org account).
https://svn.jboss.org/repos/jbossas/projects/mc-script/trunk/src/main/java/org/jboss/beans/script/ScriptValueMetaData.java

You should be able to work out how to use it from the xsd
https://svn.jboss.org/repos/jbossas/projects/mc-script/trunk/src/main/resources/schema/
or the tests
https://svn.jboss.org/repos/jbossas/projects/mc-script/trunk/src/test/resources/org/jboss/test/beans/script/test/

Here I'll explain how it works.

The extension point is that a property (or parameter or collection element) configuration
takes any ValueMetadata because it is defined in the xml to be an xsd:any element.

Using the JBossXB annotations to define an xml group
(you don't actually need the group, a plain type with a getter/setter marked @XmlAnyElement will also work if it is not of type DOM element)

  | @JBossXmlGroup
  | ({
  |    @JBossXmlChild(name="array", type=AbstractArrayMetaData.class),
  |    @JBossXmlChild(name="collection", type=AbstractCollectionMetaData.class),
  |    @JBossXmlChild(name="inject", type=AbstractInjectionValueMetaData.class),
  |    @JBossXmlChild(name="list", type=AbstractListMetaData.class),
  |    @JBossXmlChild(name="map", type=AbstractMapMetaData.class),
  |    @JBossXmlChild(name="null", type=AbstractValueMetaData.class),
  |    @JBossXmlChild(name="set", type=AbstractSetMetaData.class),
  |    @JBossXmlChild(name="this", type=ThisValueMetaData.class),
  |    @JBossXmlChild(name="value", type=StringValueMetaData.class),
  |    @JBossXmlChild(name="value-factory", type= AbstractValueFactoryMetaData.class)
  | })
  | @JBossXmlGroupText(wrapper= StringValueMetaData.class, property="value")
  | 
  | // HERE!
  | 
  | @JBossXmlGroupWildcard(wrapper= AbstractValueMetaData.class, property="value") public interface ValueMetaData extends JBossInterface, MetaDataVisitorNode
  | 
and in the xsd

  | 
  | 
  |    <xsd:group name="valueGroup">
  | 
  | 
  | <snipped/>
  | 
  | 
  |          <xsd:any namespace="##other" processContents="strict">
  | 
  |             <xsd:annotation>
  | 
  |                <xsd:documentation>An extension value</xsd:documentation>
  | 
  |             </xsd:annotation>
  | 
  |          </xsd:any>
  | 
  |       </xsd:choice>
  | 
  |    </xsd:group>
  | 

This means I can create a new subclass of ValueMetaData in its own xml namespace
and use it anywhere a "ValueGroup" is defined in the xml (or equivalently a property
is of type ValueMetaData - or a collection of them).

This is what I've done with the ScriptValueMetaData that invokes a script
to determine the value.


  | @JBossXmlSchema(namespace="urn:jboss:bean-deployer:script:2.0", elementFormDefault=XmlNsForm.QUALIFIED)
  | @XmlRootElement(name="script")
  | @XmlType(name="scriptType", propOrder="parameters")
  | public class ScriptValueMetaData extends AbstractValueMetaData
  | 

The example is slightly more complicated than it needs to be since I added an
extra feature so you can pass parameters (including injections from other beans)
which means it has to handle visiting the children of the metadata (the parameters)
and a few other bits and pieces like making the "controllerContext" available as a
variable to the script.

Without those complications, you can see that all the work is just in getValue(TypeInfo, ClassLoader).

There are a number of other places within the microcontainer and deployment
or classloader metadata that can be extended in this way, e.g. the classloader
requirement/capabilities.

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