How to add the ability to put EL expressions in Navigation Rules

Question

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.

Answer 1

CraigRPeters wrote:
Comments are welcome.Nice stuff. But that means that navigation is hardwired in the backing bean instead of faces-config.xml. Forget this comment if you've maintained a propertiesfile/configurationfile for that.
I just didn't see any other way to dynamically go back to an arbitrary page.You can declare more than one from-outcome and/or from-action for one from-view-id.