to.networld.scrawler.common.RDFParser.java Source code

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Here is the source code for to.networld.scrawler.common.RDFParser.java

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/**
 * Semantic Crawler Library
 *
 * Copyright (C) 2010 by Networld Project
 * Written by Alex Oberhauser <oberhauseralex@networld.to>
 * All Rights Reserved
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by 
 * the Free Software Foundation, version 3 of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of 
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this software.  If not, see <http://www.gnu.org/licenses/>
 */

package to.networld.scrawler.common;

import java.net.URL;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Vector;

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import org.jaxen.JaxenException;
import org.jaxen.SimpleNamespaceContext;
import org.jaxen.XPath;
import org.jaxen.dom4j.Dom4jXPath;

/**
 * Superclass that hides the low level RDF parsing code. Each class that needs to parse
 * RDF files should extend this class.
 * 
 * @author Alex Oberhauser
 */
public class RDFParser {
    protected final URL url;
    private final SAXReader reader;
    private final Document document;
    protected final HashMap<String, String> namespace = new HashMap<String, String>();
    protected String queryPrefix = "/";

    protected RDFParser(URL _url) throws DocumentException {
        this.reader = new SAXReader();
        this.setReaderOptions();
        this.url = _url;
        this.document = this.reader.read(_url);
        this.initDefaultNamespace();
    }

    /**
     * Set optimized reader options to be able to parse the files faster.
     */
    private synchronized void setReaderOptions() {
        this.reader.setValidation(false);
        this.reader.setIgnoreComments(true);
        this.reader.setIncludeExternalDTDDeclarations(false);
        this.reader.setIncludeInternalDTDDeclarations(false);
        this.reader.setStripWhitespaceText(true);
    }

    protected synchronized void initDefaultNamespace() {
        this.namespace.put("rdf", Ontologies.rdfURI);
        this.namespace.put("rdfs", Ontologies.rdfsURI);
        this.namespace.put("owl", Ontologies.owlURI);
    }

    @SuppressWarnings("unchecked")
    protected synchronized List<Element> getLinkNodes(String _query, HashMap<String, String> _namespaces) {
        try {
            XPath xpath = new Dom4jXPath(_query);
            xpath.setNamespaceContext(new SimpleNamespaceContext(_namespaces));
            return (List<Element>) xpath.selectNodes(this.document);
        } catch (JaxenException e) {
            e.printStackTrace();
            return new LinkedList<Element>();
        }
    }

    @SuppressWarnings("unchecked")
    protected synchronized List<Element> getLinkNodes(String _query) {
        return (List<Element>) this.document.selectNodes(_query);
    }

    /**
     * Please set before you call the function the variables this.namespace and this.queryPrefix.
     * 
     * @param _nodeName The name of the node for example 'dive:name'
     * @return The string representation of the given node.
     */
    protected synchronized String getSingleNode(String _nodeName) {
        List<Element> nodeList = this.getLinkNodes(this.queryPrefix + "/" + _nodeName, this.namespace);
        if (nodeList.size() > 0)
            return nodeList.get(0).getTextTrim();
        else
            return null;
    }

    protected synchronized String getConditionalSingleNode(String _nodeName, String _resourceName,
            String _resourceValue) {
        List<Element> nodeList = this.getLinkNodes(this.queryPrefix + "/" + _nodeName, this.namespace);
        if (nodeList.size() > 0) {
            for (Element node : nodeList) {
                if (node.valueOf("@" + _resourceName).equalsIgnoreCase(_resourceValue))
                    return node.getTextTrim();
            }
        }
        return null;
    }

    /**
     * Please set before you call the function the variables this.namespace and this.queryPrefix.
     * 
     * @param _nodeName The name of the node for example 'dive:name'
     * @return The string representation of the given node. If found more than one times the Vector has more elements.
     */
    protected synchronized Vector<String> getNodes(String _nodeName) {
        List<Element> nodeList = this.getLinkNodes(this.queryPrefix + "/" + _nodeName, this.namespace);
        Vector<String> retValues = new Vector<String>();
        for (Element entry : nodeList) {
            String str = entry.getTextTrim();
            if (!str.equals(""))
                retValues.add(str);
        }
        return retValues;
    }

    /**
     * Please set before you call the function the variables this.namespace and this.queryPrefix.
     * 
     * @param _nodeName The name of the node for example 'dive:name'
     * @return The resource as string representation of the given node.
     */
    protected synchronized String getSingleNodeResource(String _nodeName, String _resourceName) {
        List<Element> nodeList = this.getLinkNodes(this.queryPrefix + "/" + _nodeName, this.namespace);
        if (nodeList.size() > 0)
            return nodeList.get(0).valueOf("@" + _resourceName);
        else
            return null;
    }

    /**
     * Please set before you call the function the variables this.namespace and this.queryPrefix.
     * 
     * @param _nodeName The name of the node for example 'dive:name'
     * @return The resource as string representation of the given node. If found more than one times the Vector has more elements.
     */
    protected synchronized Vector<String> getNodesResource(String _nodeName, String _resourceName) {
        List<Element> nodeList = this.getLinkNodes(this.queryPrefix + "/" + _nodeName, this.namespace);
        Vector<String> retValues = new Vector<String>();
        for (Element entry : nodeList) {
            String str = entry.valueOf("@" + _resourceName);
            if (!str.equals(""))
                retValues.add(str);
        }
        return retValues;
    }

    public synchronized URL getURL() {
        return this.url;
    }
}