Java EE (Java Enterprise Edition) General Discussion

I had a need to dynamically determine what page to return to in a JSF application. There has to be an easier way, but here's how I wanted to do it. I wanted to put an EL expression in my <to-view-id> nav rules in the JSF config file (e.g. faces-config.xml). This isn't allowed. So I built my own custom ViewHandler to do it.

1) Define the ViewHandler in faces-config.xml:

	<application>
		...
		<view-handler>com.msd.tts.pluggable.MyDynamicViewHandler</view-handler>
	</application>

2) Create the class:

package com.msd.tts.pluggable;

import java.io.IOException;
import java.util.Locale;

import javax.faces.*;
import javax.faces.application.ViewHandler;
import javax.faces.component.UIViewRoot;
import javax.faces.context.*;
import javax.faces.el.ValueBinding;

import com.sun.faces.util.Util;

/**
 * Adds ability to put EL expressions in the <to-view-id> Navigation Rules in JSF 
 * configuration file (faces-config.xml).
 * 
 * @author		Craig Peters
 * @version		1.0
 * 
 */

public class MyDynamicViewHandler extends ViewHandler {

    /**
     * The original handler we are customizing.
     */
    private ViewHandler prevHandler = null;
    
    /** Creates a new instance of MappingViewHandler. By including
     * a parameter of the same type, we encourage the JSF framework
     * to pass a reference of the previously used ViewHandler. This way
     * we can use all the previous functionality and override only the
     * method we are interested in (in this case, the getActionURL() method).
     */
	public MyDynamicViewHandler(ViewHandler prevHandler) {
		this.prevHandler = prevHandler;
	}
    
	@Override
	public String getActionURL(FacesContext context, String viewId) {
		return prevHandler.getActionURL(context, viewId);
	}
	
	@Override
	public Locale calculateLocale(FacesContext context) {
		return prevHandler.calculateLocale(context);
	}

	@Override
	public String calculateRenderKitId(FacesContext context) {
		return prevHandler.calculateRenderKitId(context);
	}

	@Override
	public UIViewRoot createView(FacesContext context, String viewId) {
		return prevHandler.createView(context, viewId);
	}

	@Override
	public String getResourceURL(FacesContext context, String path) {
		return prevHandler.getResourceURL(context, path);
	}

	@Override
	public void renderView(FacesContext context, UIViewRoot viewToRender)
			throws IOException, FacesException {
		
		String result = viewToRender.getViewId();
		
		if (Util.isVBExpression(viewToRender.getViewId())) {
			ValueBinding vb = context.getApplication().createValueBinding(viewToRender.getViewId());
			result = vb.getValue(context).toString();
		}
		
		if (result.charAt(0) != '/')
			throw new IllegalArgumentException("Illegal view ID " + result + ". The ID must begin with '/'");

		viewToRender.setViewId(result);
		
		prevHandler.renderView(context, viewToRender);
	}

	@Override
	public UIViewRoot restoreView(FacesContext context, String viewId) {
		return prevHandler.restoreView(context, viewId);
	}

	@Override
	public void writeState(FacesContext context) throws IOException {
		prevHandler.writeState(context);
	}
	
}

3) Use EL in navigation rules:

	<navigation-rule>
		<from-view-id>/CommonForm.jsp</from-view-id>
		<navigation-case>
			<to-view-id>#{bean.caller}</to-view-id>
		</navigation-case>
	</navigation-rule>

The "bean.caller" method will have saved the page to go back to.

Comments are welcome. I just didn't see any other way to dynamically go back to an arbitrary page.

Thanks.