com.tonbeller.jpivot.core.ModelFactory.java Source code

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Here is the source code for com.tonbeller.jpivot.core.ModelFactory.java

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/*
 * ====================================================================
 * This software is subject to the terms of the Common Public License
 * Agreement, available at the following URL:
 *   http://www.opensource.org/licenses/cpl.html .
 * Copyright (C) 2003-2004 TONBELLER AG.
 * All Rights Reserved.
 * You must accept the terms of that agreement to use this software.
 * ====================================================================
 *
 * 
 */
package com.tonbeller.jpivot.core;

import java.io.IOException;
import java.net.URL;

import org.apache.commons.digester.Digester;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

/**
 * creates a model instance from an xml description. Example
 * <pre>
 * &lt;?xml version="1.0" encoding="utf-8"?&gt;
 * &lt;model id="m1" class="com.tonbeller.jpivot.core.ModelSupport"&gt;
 *   &lt;extension id="f1" class="com.tonbeller.jpivot.core.ExtensionSupport"/&gt;
 *   &lt;extension id="f2" class="com.tonbeller.jpivot.core.ExtensionSupport"/&gt;
 * &lt;/model&gt;
 * </pre>
 * @author av
 */

public class ModelFactory {

    /**
     * singleton
     */
    private ModelFactory() {
    }

    /**
     * not for external use. Has to be public for the commons digester
     * to access it.
     */
    public static class ModelHolder {
        private Model model;

        public void setModel(Model model) {
            this.model = model;
        }

        public Model getModel() {
            return model;
        }
    }

    /**
     * creates a model from an xml configuration file
     * @param url url of model configuration file
     * @return Model
     * @throws SAXException
     * @throws IOException
     */
    public static Model instance(URL url) throws SAXException, IOException {
        Digester digester = new Digester();
        digester.setValidating(false);

        ModelHolder root = new ModelHolder();
        digester.push(root);

        digester.addObjectCreate("model", "missing \"class\" attribute", "class");
        digester.addSetProperties("model");
        digester.addSetNext("model", "setModel");

        digester.addObjectCreate("model/extension", "missing \"class\" attribute", "class");
        digester.addSetProperties("model/extension");
        digester.addSetNext("model/extension", "addExtension");

        InputSource is = new InputSource(url.toExternalForm());
        digester.parse(is);
        return root.getModel();
    }

}