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/*
 * The contents of this file are subject to the terms 
 * of the Common Development and Distribution License 
 * (the License).  You may not use this file except in
 * compliance with the License.
 * 
 * You can obtain a copy of the license at 
 * https://jsftemplating.dev.java.net/cddl1.html or
 * jsftemplating/cddl1.txt.
 * See the License for the specific language governing 
 * permissions and limitations under the License.
 * 
 * When distributing Covered Code, include this CDDL 
 * Header Notice in each file and include the License file 
 * at jsftemplating/cddl1.txt.  
 * If applicable, add the following below the CDDL Header, 
 * with the fields enclosed by brackets [] replaced by
 * you own identifying information: 
 * "Portions Copyrighted [year] [name of copyright owner]"
 * 
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 */
package com.sun.jsftemplating.el;

import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;

import javax.faces.component.UIViewRoot;
import javax.faces.context.FacesContext;
import javax.faces.el.EvaluationException;
import javax.faces.el.VariableResolver;


/**
 *  	This VariableResolver exists to resolve "page session"
 *	attributes.  This concept, borrowed from NetDynamics / JATO, stores
 *	data w/ the page so that it is available throughout the life of the
 *	page.  This is longer than request scope, but usually shorter than
 *	session.  This implementation stores the attributes on the
 *	UIViewRoot.
 *
 *  @author Ken Paulsen ([email protected])
 */
public class PageSessionResolver extends VariableResolver {

    /**
     *	 Constructor.
     */
    public PageSessionResolver(VariableResolver orig) {
	super();
	_origVariableResolver = orig;
    }

    /**
     *	 This first delegates to the original VariableResolver,
     *	    it then checks "page session" to see if the value exists.
     */
    public Object resolveVariable(FacesContext context, String name) throws EvaluationException {
	Object result = null;
	// Check to see if expression explicitly asks for PAGE_SESSION
	if (name.equals(PAGE_SESSION)) {
	    // It does, return the Map
	    UIViewRoot root = context.getViewRoot();
	    result = getPageSession(context, root);
	    if (result == null) {
		// No Map!  That's ok, create one...
		result = createPageSession(context, root);
	    }
	} else {
	    if (_origVariableResolver != null) {
		// Not explicit, let original resolver do its thing first...
		result = _origVariableResolver.resolveVariable(context, name);
	    }

	    if (result == null) {
		// Original resolver couldn't find anything, check page session
		Map map =
		    getPageSession(context, (UIViewRoot) null);
		if (map != null) {
		    result = map.get(name);
		}
	    }
	}
	return result;
    }

    /**
     *	 This method provides access to the "page session"
     *	    Map.  If it doesn't exist, it returns
     *	    null.  If the given UIViewRoot is null,
     *	    then the current UIViewRoot will be used.
     */
    public static Map getPageSession(FacesContext ctx, UIViewRoot root) {
	if (root == null) {
	    root = ctx.getViewRoot();
	}
	return (Map)
	    root.getAttributes().get(PAGE_SESSION_KEY);
    }

    /**
     *	 This method will create a new "page session" Map.  It
     *	    will overwrite any existing "page session" Map, so be
     *	    careful.
     */
    public static Map createPageSession(FacesContext ctx, UIViewRoot root) {
	if (root == null) {
	    root = ctx.getViewRoot();
	}
	// Create it...
	Map map = new HashMap(4);

	// Store it...
	root.getAttributes().put(PAGE_SESSION_KEY, map);

	// Return it...
	return map;
    }

    /**
     *	 The original VariableResolver.
     */
    private VariableResolver _origVariableResolver = null;

    /**
     *	 The attribute key in which to store the "page" session Map.
     */
    private static final String PAGE_SESSION_KEY	= "_ps";

    /**
     *	 The name an expression must use when it explicitly specifies page
     *	    session. ("pageSession")
     */
    public static final String PAGE_SESSION		= "pageSession";
}