Ravi Vyas Ravi Vyas - 1 month ago 12
Java Question

HTTP Status 500 - Servlet execution threw an exception

I am getting this error while calling a java class in servlet.

Here is the error.

type Exception report

message Servlet execution threw an exception

description The server encountered an internal error that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: Servlet execution threw an exception
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

root cause

java.lang.NoClassDefFoundError: com/hp/hpl/jena/query/QueryFactory
com.complexible.common.csv.MuseumData.gts(MuseumData.java:109)
com.complexible.common.csv.MuseumData.ass(MuseumData.java:89)
com.complexible.common.csv.MuseumRDF.doGet(MuseumRDF.java:48)
javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

root cause

java.lang.ClassNotFoundException: com.hp.hpl.jena.query.QueryFactory
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1720)
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1571)
com.complexible.common.csv.MuseumData.gts(MuseumData.java:109)
com.complexible.common.csv.MuseumData.ass(MuseumData.java:89)
com.complexible.common.csv.MuseumRDF.doGet(MuseumRDF.java:48)
javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

note The full stack trace of the root cause is available in the Apache Tomcat/7.0.55 logs.


Here is a code of my java class which will get the record from a RDF file using SPARQL and will return the output in JSON format in the console, then after i would catch the output and convert it into the string hence i could use that string into the servlet.

package com.complexible.common.csv;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintStream;
import java.lang.NoClassDefFoundError;
import com.hp.hpl.jena.query.Query;
import com.hp.hpl.jena.query.QueryExecution;
import com.hp.hpl.jena.query.QueryExecutionFactory;
import com.hp.hpl.jena.query.QueryFactory;
import com.hp.hpl.jena.query.ResultSet;
import com.hp.hpl.jena.query.ResultSetFormatter;
import com.hp.hpl.jena.rdf.model.Model;
import com.hp.hpl.jena.rdf.model.ModelFactory;

public class MuseumData {
public static void main( String[] args ) throws IOException {


String output=getrec();
System.out.println(output);
}


public static String getrec() throws IOException
{
String spr="prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>\n"+
"prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>\n"+
"prefix crm: <http://www.cidoc-crm.org/cidoc-crm/>\n"+
"prefix owl: <http://www.w3.org/2002/07/owl#>\n"+
"prefix xsd: <http://www.w3.org/2001/XMLSchema#>\n"+
"prefix crm: <http://www.cidoc-crm.org/rdfs/cidoc_crm_v5.0.4_official_release.rdfs#>\n"+
"\n"+
//?title ?person ?type instead of *
"SELECT * WHERE { <http://phdprototype.tk/collectionimage/4D0BFF17-5810-4644-A550-D35EE090D4A8.png>"+
"crm:P3_has_note ?title ; "+
"crm:E21_Person ?person ;"+
"crm:E62_String ?type ;"+
"crm:P82_at_some_time_within ?year;"+
"crm:P33_used_specific_technique ?material;}";

Query query = QueryFactory.create(spr);

Model model = ModelFactory.createDefaultModel();

File f = new File("J:/Museum/data.rdf");
model.read(new FileInputStream(f), "RDF/XML");

//model.write(System.out, "TTL");

final QueryExecution exec = QueryExecutionFactory.create(query, model);
//ResultSetFormatter.out(System.out, exec.execSelect(), query);


ByteArrayOutputStream baos = new ByteArrayOutputStream();
PrintStream ps = new PrintStream(baos);
// IMPORTANT: Save the old System.out!
PrintStream old = System.out;
// Tell Java to use your special stream
System.setOut(ps);
// Print some output: goes to your special stream
ResultSetFormatter.outputAsJSON(System.out, exec.execSelect());
// Put things back
System.out.flush();
System.setOut(old);
// Show what happened

// return baos.toString();

String gcr=baos.toString();
return gcr;

}

}


Here is a servlet code which will display the output in a browser.

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub

PrintWriter out= response.getWriter();
String rec=MuseumData.getrec();
out.print(rec);


}

Answer

Find the .jar for com/hp/hpl/jena/query/QueryFactory and put it in WEB-INF lib in your .war file.

Here's how to do it if you happened to be developing your servlets in the Eclipse IDE:

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