Metawidget: Collections Support Part 2

I was recently asked:

"I would like to create a widget that displays each item contained in a List using an ICEfaces PanelTabSet. I would like the widget inside each panelTab to be generated through Metawidget. How can I accomplish this?"

This represents (yet) another aesthetic preference for rendering Collections. Namely, rendering one item per tab. Some other preferences, such as rendering one item per row of a table, have been covered in a previous blog entry). As I said in that entry:

To support this, Metawidget provides WidgetBuilders.

So it's a case of writing a WidgetBuilder that will return a PanelTabSet for the List. I have put together a complete project you can download here. It'll produce something that looks like this:

Code for the WidgetBuilder part below:

package com.myapp;

import static org.metawidget.inspector.InspectionResultConstants.*;

import java.util.List;
import java.util.Map;

import javax.el.ELContext;
import javax.el.ExpressionFactory;
import javax.el.ValueExpression;
import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;

import org.metawidget.faces.FacesUtils;
import org.metawidget.faces.component.UIMetawidget;
import org.metawidget.faces.component.UIStub;
import org.metawidget.faces.component.html.HtmlMetawidget;
import org.metawidget.util.ClassUtils;
import org.metawidget.util.simple.StringUtils;
import org.metawidget.widgetbuilder.iface.WidgetBuilder;

import com.icesoft.faces.component.paneltabset.PanelTab;
import com.icesoft.faces.component.paneltabset.PanelTabSet;

public class IceFacesTabsWidgetBuilder
   implements WidgetBuilder<UIComponent, UIMetawidget> {

   //
   // Public methods
   //

   @Override
   public UIComponent buildWidget( String elementName, Map<String, String> attributes, UIMetawidget metawidget ) {

      // Not for us?

      String type = attributes.get( TYPE );

      if ( type == null ) {
         return null;
      }

      Class<?> clazz = ClassUtils.niceForName( type );

      if ( !List.class.isAssignableFrom( clazz ) ) {
         return null;
      }

      // Create a Stub to wrap around the PanelTabSet.
      //
      // This is because:
      //
      // 1. PanelTabSet will not switch tabs if it is destroyed/recreated. We must set
      // COMPONENT_ATTRIBUTE_NOT_RECREATABLE on it (see
      // http://metawidget.sourceforge.net/doc/reference/en/html/ch02s04.html#section-architecture-widgetbuilders-implementing-your-own-faces).
      // This limits some dynamicism, such as being able to dynamically add tabs, but there are
      // further ways around that
      //
      // 2. COMPONENT_ATTRIBUTE_NOT_RECREATABLE only works if there is a 'value' expression that
      // OverriddenWidgetBuilder can match against
      //
      // 3. PanelTabSet is a little unusual in how it treats its 'value' expression (binding it to
      // a UI mechanism, rather than a model mechanism) so we need to avoid using it. We use the
      // Stub's 'value' expression instead

      UIStub stub = new UIStub();

      FacesContext context = FacesContext.getCurrentInstance();
      ELContext elContext = context.getELContext();
      ValueExpression metawidgetValueExpression = metawidget.getValueExpression( "value" );
      String metawidgetValueExpressionString = FacesUtils.unwrapExpression( metawidgetValueExpression.getExpressionString() );
      ExpressionFactory expressionFactory = context.getApplication().getExpressionFactory();
      String tabSetValueExpressionString = metawidgetValueExpressionString + StringUtils.SEPARATOR_DOT_CHAR + attributes.get( NAME );
      ValueExpression tabSetValueExpression = expressionFactory.createValueExpression( elContext, FacesUtils.wrapExpression( tabSetValueExpressionString ), Object.class );

      stub.setValueExpression( "value", tabSetValueExpression );

      // Create tab set

      PanelTabSet panelTabSet = new PanelTabSet();
      panelTabSet.getAttributes().put( UIMetawidget.COMPONENT_ATTRIBUTE_NOT_RECREATABLE, true );
      stub.getChildren().add( panelTabSet );
      List<UIComponent> tabs = panelTabSet.getChildren();

      // Lookup the List from the parent Metawidget to see how many items it has

      List<?> list = (List<?>) tabSetValueExpression.getValue( elContext );

      // Create one tab per item...

      for ( int loop = 0, length = list.size(); loop < length; loop++ ) {

         PanelTab tab = new PanelTab();
         tabs.add( tab );

         // ...with each tab itself containing a Metawidget.
         //
         // The 'value' expression of each Metawidget uses the EL #{foo.bar[0]} notation for
         // accessing arrays

         HtmlMetawidget tabMetawidget = new HtmlMetawidget();
         ValueExpression tabValueExpression = expressionFactory.createValueExpression( elContext, FacesUtils.wrapExpression( tabSetValueExpressionString + '[' + loop + ']' ), Object.class );
         tabMetawidget.setValueExpression( "value", tabValueExpression );
         tabMetawidget.setValueExpression( "readOnly", metawidget.getValueExpression( "readOnly" ) );
         tab.getChildren().add( tabMetawidget );
      }

      // Return tab set

      return stub;
   }
}