Setting the var attribute of dataTable in a facelet

I'm currently working on a small little facelets suite to aid in portlet development. Initially, the idea is just to focus on making correct use of the portlet CSS styles implicit. So, for example, the following is the kind of code needed to set the portlet tables styles for the h:dataTable JSF component:

   <h:dataTable value="#{mybean.myData}" var="row"
     styleClass="portlet-section-body"
     rowClasses="portlet-section-body,portlet-section-alternate"
     headerClass="portlet-section-header">

So, I'd like to replace that with a facelet instead, so that it looks like this:

   <p:dataTable value="#{mybean.myData}" var="row">

And the facelet would be defined once in a .xhtml file as:

<ui:composition>
    <h:dataTable value="#{value}" var="#{var}"
      styleClass="portlet-section-body"
      rowClasses="portlet-section-body,portlet-section-alternate"
      headerClass="portlet-section-header">
        <ui:insert />
    </h:dataTable>
</ui:composition>

However, this doesn't quite work. The problem is that it tries to set the var attribute of the dataTable component to a value expression, but dataTable requires a simple string for var. So we have to figure out some way of getting the var variable from the facelet into the dataTable component. What I came up with was a custom TagHandler that evaluates the value expression and then sets the var property of the dataTable component directly:

package portletfacelets;

import java.io.IOException;

import javax.el.ELException;
import javax.faces.FacesException;
import javax.faces.component.UIComponent;
import javax.faces.component.html.HtmlDataTable;

import com.sun.facelets.FaceletContext;
import com.sun.facelets.FaceletException;
import com.sun.facelets.tag.TagAttribute;
import com.sun.facelets.tag.TagConfig;
import com.sun.facelets.tag.TagHandler;

public class SetVarHandler extends TagHandler {

    private final TagAttribute var;

    public SetVarHandler(TagConfig config) {
        super(config);
        this.var = this.getAttribute("var");
    }
    public void apply(FaceletContext ctx, UIComponent parent)
            throws IOException, FacesException, FaceletException, ELException {

        System.out.println("var=" + this.var.getValue(ctx));
        
        if (parent instanceof HtmlDataTable) {
            HtmlDataTable table = (HtmlDataTable) parent;
            table.setVar(this.var.getValue(ctx));
        }
        

        this.nextHandler.apply(ctx, parent);
    }

}

I add this to my facelets taglib.xml file as such:

  <tag>
    <tag-name>setVar</tag-name>
    <handler-class>portletfacelets.SetVarHandler</handler-class>
  </tag>

And then use it like this in my facelet:

<ui:composition>
    <h:dataTable value="#{value}"
      styleClass="portlet-section-body"
      rowClasses="portlet-section-body,portlet-section-alternate"
      headerClass="portlet-section-header">
        <p:setVar var="#{var}" />
        <ui:insert />
    </h:dataTable>
</ui:composition>

Voila! However, seeing as this might come in handy in future instances, I wondered if I couldn't make something a bit more generic. So I created this TagHandler:

package portletfacelets;

import java.io.IOException;
import java.lang.reflect.Method;

import javax.el.ELException;
import javax.faces.FacesException;
import javax.faces.component.UIComponent;

import com.sun.facelets.FaceletContext;
import com.sun.facelets.FaceletException;
import com.sun.facelets.tag.TagAttribute;
import com.sun.facelets.tag.TagConfig;
import com.sun.facelets.tag.TagHandler;

public class SetValueHandler extends TagHandler {

    private final TagAttribute methodName;
    private final TagAttribute value;

    public SetValueHandler(TagConfig config) {
        super(config);
        this.methodName = this.getRequiredAttribute("methodName");
        this.value = this.getRequiredAttribute("value");
    }
    public void apply(FaceletContext ctx, UIComponent parent)
            throws IOException, FacesException, FaceletException, ELException {
        try {
            
            Method m = parent.getClass().getMethod(this.methodName.getValue(ctx), 
                    new Class[]{String.class});
            m.invoke(parent, new Object[]{this.value.getValue(ctx)});
            
        } catch (Exception e) {
            e.printStackTrace();
        }

        this.nextHandler.apply(ctx, parent);
    }

}

So I'm using reflection to call any method on the parent JSF component and passing in the specified value. Then I use it in my facelet like so:

<ui:composition>
    <h:dataTable value="#{value}"
      styleClass="portlet-section-body"
      rowClasses="portlet-section-body,portlet-section-alternate"
      headerClass="portlet-section-header">
        <p:setValue methodName="setVar" value="#{var}" />
        <ui:insert />
    </h:dataTable>
</ui:composition>

There you have it. Turns out there is more than one way to skin this cat, so I'll also share in a future blog post a different approach to this issue.