ConfigReader can construct new instances of objects. The XML element name is the Java class name and the XML namespace is the Java package. The following example constructs an org.metawidget.swing.SwingMetawidget.

<metawidget xmlns="http://metawidget.org"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://metawidget.org http://metawidget.org/xsd/metawidget-1.0.xsd">

	<swingMetawidget xmlns="java:org.metawidget.swing"/>
	
</metawidget>			

Using the XML namespace to denote the Java package allows the (optional) plugging in of XML Schema validation on a per-package basis. For example:

<swingMetawidget xmlns="java:org.metawidget.swing"
xsi:schemaLocation="java:org.metawidget.swing http://metawidget.org/xsd/org.metawidget.swing-1.0.xsd"/>

Within an object, ConfigReader can call setXXX methods. The following example calls the setOpaque method of SwingMetawidget:

<metawidget xmlns="http://metawidget.org"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://metawidget.org http://metawidget.org/xsd/metawidget-1.0.xsd">

	<swingMetawidget xmlns="java:org.metawidget.swing">
		<opaque>
			<boolean>true</boolean>
		</opaque>
	</swingMetawidget>
	
</metawidget>

Multi-parameter methods are also supported. The following example calls the setParameter method of HtmlMetawidget (it takes two arguments):

<metawidget xmlns="http://metawidget.org"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://metawidget.org http://metawidget.org/xsd/metawidget-1.0.xsd">

	<htmlMetawidget xmlns="java:org.metawidget.faces.component.html">
		<parameter>
			<string>numberOfColumns</string>
			<int>2</int>
		</parameter>		
	</htmlMetawidget>
	
</metawidget>

As alluded to in the previous section, when calling setXXX methods the XML format can specify simple types. The previous example used boolean, string and int. Also supported are:

Some environments store their resources in specialized locations that are inaccessible by normal means (ie. ClassLoader.getResource). For example, Web environments use a WEB-INF folder that must be accessed through ServletContext.getResource. Simiarly, Android environments must resolve resources using Context.getResources.

ConfigReader and its specialized subclasses, such as ServletConfigReader and AndroidConfigReader understand this distinction and provide resource resolving capability to all the objects they create. Specifically, ConfigReader implements ResourceResolver and passes itself to any xxxConfig classes that implement NeedsResourceResolver.

Metawidget dictates all Inspectors, WidgetBuilders, WidgetProcessors and Layouts be threadsafe and immutable. This is an important design decision as it means a single instance can be reused across an entire application. Immutabilty is enforced by not having any setXXX methods on the objects themselves. Rather, the setXXX methods are called on Config objects, which are then passed to the object's constructor. Once constructed, the object cannot be changed.

ConfigReader understands this distinction by way of a config attribute. The following example configures an immutable Inspector. The setInspectors method is called on org.metawidget.inspector.composite.CompositeInspectorConfig and then passed to CompositeInspector:

<compositeInspector xmlns="java:org.metawidget.inspector.composite" config="CompositeInspectorConfig">
	<inspectors>
		<array>
			<metawidgetAnnotationInspector xmlns="java:org.metawidget.inspector.annotation" />
			<propertyTypeInspector xmlns="java:org.metawidget.inspector.propertytype"/>
		</array>
	</inspectors>
</compositeInspector>

Having constructed an immutable object, ConfigReader will cache the instance and reuse it. The config attribute defaults to using the same package as the xmlns (ie. org.metawidget.inspector.composite in the example above). This can be overridden if a fully qualified classname is provided.

	Config classes must override equals and hashCode
	In order to reliably cache and reuse an immutable object that uses a config attribute, the xxxConfig class must override equals and hashCode. This is important to bear in mind when implementing your own custom objects.