com.knowledgebooks.rdf.SparqlClient.java Source code

Introduction

Here is the source code for com.knowledgebooks.rdf.SparqlClient.java

Source

package com.knowledgebooks.rdf;

import org.apache.commons.httpclient.*;
import org.apache.commons.httpclient.methods.GetMethod;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
import org.xml.sax.Attributes;

import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import java.io.IOException;
import java.io.InputStream;
import java.net.URLEncoder;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * Copyright Mark Watson 2008-2010. All Rights Reserved.
 * License: LGPL version 3 (http://www.gnu.org/licenses/lgpl-3.0.txt)
 */
public class SparqlClient extends DefaultHandler {
    public SparqlClient(String endpoint_URL, String sparql) throws Exception {
        //System.out.println("SparqlClient("+endpoint_URL+", "+sparql+")");
        HttpClient client = new HttpClient();
        client.getHttpConnectionManager().getParams().setConnectionTimeout(10000);

        String req = URLEncoder.encode(sparql, "utf-8");
        HttpMethod method = new GetMethod(endpoint_URL + "?query=" + req);
        method.setFollowRedirects(false);
        try {
            client.executeMethod(method);
            //System.out.println(method.getResponseBodyAsString());
            //if (true) return;
            InputStream ins = method.getResponseBodyAsStream();
            SAXParserFactory factory = SAXParserFactory.newInstance();
            SAXParser sax = factory.newSAXParser();
            sax.parse(ins, this);
        } catch (HttpException he) {
            System.err.println("Http error connecting to '" + endpoint_URL + "'");
        } catch (IOException ioe) {
            System.err.println("Unable to connect to '" + endpoint_URL + "'");
        }
        method.releaseConnection();
    }

    private List<Map<String, String>> variableBindings = new ArrayList<Map<String, String>>();
    private Map<String, String> tempBinding = null;
    private String tempVariableName = null;
    private String lastElementName = null;

    public void startElement(String uri, String localName, String qName, Attributes attributes)
            throws SAXException {
        //System.out.println("startElement " + qName);
        if (qName.equalsIgnoreCase("result")) {
            tempBinding = new HashMap<String, String>();
        }
        if (qName.equalsIgnoreCase("binding")) {
            tempVariableName = attributes.getValue("name");
        }
        lastElementName = qName;
    }

    public void endElement(String uri, String localName, String qName) throws SAXException {
        if (qName.equalsIgnoreCase("result")) {
            if (!variableBindings.contains(tempBinding))
                variableBindings.add(tempBinding);
        }
    }

    public void characters(char[] ch, int start, int length) throws SAXException {
        String s = new String(ch, start, length).trim();
        if (s.length() > 0) {
            if ("literal".equals(lastElementName))
                tempBinding.put(tempVariableName, s);
            if ("uri".equals(lastElementName))
                tempBinding.put(tempVariableName, "<" + s + ">");
        }
    }

    public List<Map<String, String>> variableBindings() {
        return variableBindings;
    }
}