org.danann.cernunnos.xml.ValueOfPhrase.java Source code

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Here is the source code for org.danann.cernunnos.xml.ValueOfPhrase.java

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/*
 * Copyright 2007 Andrew Wills
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.danann.cernunnos.xml;

import org.danann.cernunnos.AttributePhrase;
import org.danann.cernunnos.Attributes;
import org.danann.cernunnos.CacheHelper;
import org.danann.cernunnos.DynamicCacheHelper;
import org.danann.cernunnos.EntityConfig;
import org.danann.cernunnos.Formula;
import org.danann.cernunnos.Phrase;
import org.danann.cernunnos.Reagent;
import org.danann.cernunnos.ReagentType;
import org.danann.cernunnos.SimpleFormula;
import org.danann.cernunnos.SimpleReagent;
import org.danann.cernunnos.TaskRequest;
import org.danann.cernunnos.TaskResponse;
import org.dom4j.Node;
import org.dom4j.XPath;

/**
 * <code>PhraseComponent</code> implementation that evaluates by performing an 
 * XPATH query on the NODE node and returns the textual value of the 
 * identified node(s).
 */
public final class ValueOfPhrase implements Phrase {

    // Instance Members.
    private CacheHelper<String, XPath> xpathCache;
    private Phrase source;
    private Phrase expression;

    /*
     * Public API.
     */

    public static final Reagent SOURCE = new SimpleReagent("NODE", "@source", ReagentType.PHRASE, Node.class,
            "Optional source node against which the EXPRESSION will be evaluated.  If not "
                    + "provided, the value of the 'Attributes.NODE' request attribute will be used.",
            new AttributePhrase(Attributes.NODE));

    public static final Reagent EXPRESSION = new SimpleReagent("EXPRESSION", "descendant-or-self::text()",
            ReagentType.PHRASE, String.class, "An XPath expression that describes a node.");

    public Formula getFormula() {
        Reagent[] reagents = new Reagent[] { CacheHelper.CACHE, CacheHelper.CACHE_MODEL, SOURCE, EXPRESSION };
        return new SimpleFormula(ValueOfPhrase.class, reagents);
    }

    public void init(EntityConfig config) {

        // Instance Members.
        this.xpathCache = new DynamicCacheHelper<String, XPath>(config);
        this.source = (Phrase) config.getValue(SOURCE);
        this.expression = (Phrase) config.getValue(EXPRESSION);

    }

    public Object evaluate(TaskRequest req, TaskResponse res) {

        Node src = (Node) source.evaluate(req, res);
        final String xpathExpresion = (String) expression.evaluate(req, res);
        final XPath xpath = this.xpathCache.getCachedObject(req, res, xpathExpresion, XPathCacheFactory.INSTANCE);
        try {
            xpath.setVariableContext(new RequestVariableContext(req));
            return xpath.valueOf(src);
        } finally {
            xpath.setVariableContext(null);
        }

    }

}