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POProblems connecting with Dbpedia Lookup web service
 

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  1. POProblems connecting with Dbpedia Lookup web service
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    <p>I'm trying to use the Lookup web service from DBpedia, but I'm finding difficulties because there's very little information on the web. I found a code example, but when I execute it, I get errors:</p> <pre><code>java.lang.NullPointerException at tutorial.DBpediaLookupClient.containsSearchTerms(DBpediaLookupClient.java:111) at tutorial.DBpediaLookupClient.endElement(DBpediaLookupClient.java:87) at org.apache.xerces.parsers.AbstractSAXParser.endElement(Unknown Source) at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanEndElement(Unknown Source) at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(Unknown Source) at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source) at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source) at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source) at org.apache.xerces.parsers.XMLParser.parse(Unknown Source) at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source) at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source) at org.apache.xerces.jaxp.SAXParserImpl.parse(Unknown Source) at javax.xml.parsers.SAXParser.parse(SAXParser.java:195) at tutorial.DBpediaLookupClient.&lt;init&gt;(DBpediaLookupClient.java:56) at tutorial.DBpediaLookupClient.main(DBpediaLookupClient.java:126) </code></pre> <p><strong>HERE IS THE CODE:</strong></p> <pre class="lang-java prettyprint-override"><code>package tutorial; 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; import java.util.StringTokenizer; import javax.xml.parsers.SAXParser; import javax.xml.parsers.ParserConfigurationException; import javax.xml.parsers.SAXParserFactory; import org.apache.commons.httpclient.HttpClient; import org.apache.commons.httpclient.HttpException; import org.apache.commons.httpclient.HttpMethod; import org.apache.commons.httpclient.methods.GetMethod; import org.xml.sax.SAXException; import org.xml.sax.XMLReader; import org.xml.sax.helpers.DefaultHandler; import com.sun.org.apache.bcel.internal.classfile.Attribute; public class DBpediaLookupClient extends DefaultHandler { /** * @param args */ private List&lt;Map&lt;String, String&gt;&gt; variableBindings = new ArrayList&lt;Map&lt;String, String&gt;&gt;(); private Map&lt;String, String&gt; tempBinding = null; private String lastElementName = null; private String query = ""; public DBpediaLookupClient( String query ) throws Exception { this.query = query; HttpClient client = new HttpClient(); HttpMethod method = new GetMethod("http://lookup.dbpedia.org/api/search.asmx/KeywordSearch?QueryClass=place&amp;QueryString="+query); try{ client.executeMethod(method); System.out.println(method); InputStream ins = method.getResponseBodyAsStream(); SAXParserFactory factory = SAXParserFactory.newInstance(); javax.xml.parsers.SAXParser sax = factory.newSAXParser(); sax.parse(ins, this); }catch (HttpException he) { System.err.println("Http error connecting to lookup.dbpedia.org"); }catch (IOException ioe) { System.err.println("Unable to connect to lookup.dbpedia.org"); }catch (ParserConfigurationException e) { System.out.println("O parser não foi configurado corretamente."); e.printStackTrace(); }catch (SAXException e) { System.out.println("Problema ao fazer o parse do arquivo."); e.printStackTrace(); } method.releaseConnection(); } public void startElement(String uri, String localName, String qName, Attribute attributes) throws SAXException { if (qName.equalsIgnoreCase("result")) { tempBinding = new HashMap&lt;String, String&gt;(); } lastElementName = qName; } public void endElement(String uri, String localName, String qName) throws SAXException { if (qName.equalsIgnoreCase("result")) { System.out.println("Qname:" + qName); if (!variableBindings.contains(tempBinding) &amp;&amp; containsSearchTerms(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() &gt; 0) { if ("Description".equals(lastElementName)) tempBinding.put("Description", s); if ("URI".equals(lastElementName)) tempBinding.put("URI", s); if ("Label".equals(lastElementName)) tempBinding.put("Label", s); } } public List&lt;Map&lt;String, String&gt;&gt; variableBindings() { return variableBindings; } private boolean containsSearchTerms(Map&lt;String, String&gt; bindings) { StringBuilder sb = new StringBuilder(); for (String value : bindings.values()){ sb.append(value); // do not need white space } String text = sb.toString().toLowerCase(); StringTokenizer st = new StringTokenizer(this.query); while (st.hasMoreTokens()) { if (text.indexOf(st.nextToken().toLowerCase()) == -1) { return false; } } return true; } public static void main(String[] args) { try { DBpediaLookupClient client = new DBpediaLookupClient("berlin"); } catch (Exception e) { e.printStackTrace(); } } } </code></pre> <p>If anybody has any idea of what's wrong please help me. Or if any of you has any other code example it will help a lot too.</p>
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