I get trouble with java.lang.NullPointerException while loading n-triple file into a Jena SDB Model

Question

I've a an n-triple file that i need to store it in a database through Jena SDB Model. I've write the following code to do that. But i struggle with a java.lang.NullPointerException that I don't really have any clue about what made it to happen and how to fix it. Here is the code :

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.InputStream;

import com.hp.hpl.jena.db.DBConnection;
import com.hp.hpl.jena.ontology.OntModel;
import com.hp.hpl.jena.ontology.ProfileRegistry;
import com.hp.hpl.jena.rdf.model.Model;
import com.hp.hpl.jena.rdf.model.ModelFactory;
import com.hp.hpl.jena.rdf.model.ModelMaker;

public class JenaRepositoryManagement {

    private MySQLAccess mysql  = null;  
    private String      dbname = null;


    private String xmlbase  = "http://www.test.org/test.owl#";

    private OntModel domainModel = null;

    public JenaRepositoryManagement (String databaseName) {

        dbname = "sdb_" + databaseName;

        mysql  = new MySQLAccess();

        mysql.createDatabase(dbname);

        impotring();
    }


    public void importing() {
        // Instantiate the MySQL driver
        try {

            Class.forName("com.mysql.jdbc.Driver");


        // Create a database connection object
        DBConnection connection = new DBConnection("jdbc:mysql://localhost/"+dbname, "root", "", "MySQL");

        // Get a ModelMaker for database-backed models
        ModelMaker maker = ModelFactory.createModelRDBMaker(connection);

        Model traceModel = maker.createModel("testModel");

        // Start a database transaction. Without one, each statement will be auto-committed
        traceModel.begin();         



        InputStream in = this.getClass().getClassLoader().getResourceAsStream("data/nts/100.nt");

        traceModel.read(in, xmlbase, "N-TRIPLE");

        traceModel.write(System.out); 

        // Commit the database transaction
        traceModel.commit();



    } catch (ClassNotFoundException | FileNotFoundException e) {
        e.printStackTrace();
    }


}

}

Here is the output during the execution

CREATE DATABASE IF NOT EXISTS sdb_100_n;
java.lang.NullPointerException
    at java.io.Reader.<init>(Reader.java:78)
    at java.io.InputStreamReader.<init>(InputStreamReader.java:129)
    at com.hp.hpl.jena.util.FileUtils.asUTF8(FileUtils.java:51)
    at com.hp.hpl.jena.rdf.model.impl.NTripleReader.read(NTripleReader.java:72)
    at com.hp.hpl.jena.rdf.model.impl.ModelCom.read(ModelCom.java:226)
    at soctrace.JenaRepositoryManagement.importing(JenaRepositoryManagement.java:70)
    at soctrace.views.Main$1.run(Main.java:165)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:727)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:688)
    at java.awt.EventQueue$3.run(EventQueue.java:686)
    at java.security.AccessController.doPrivileged(Native Method)
    at java    .security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:697)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

And finally Here is a sample of the n-triple file

<http://www.test.org/test.owl#trace0> <http://www.test.org/test.owl#traceContainsEvent>     <http://www.test.org/test.owl#event0> .
<http://www.test.org/test.owl#event0> <http://www.test.org/test.owl#hasTime> <http://www.test.org/test.owl#interval0> .
<http://www.test.org/test.owl#event0> <http://www.test.org/test.owl#hasActiveTime> <http://www.test.org/test.owl#aduration0> .
<http://www.test.org/test.owl#interval0> <http://www.test.org/test.owl#hasStartTime> <http://www.test.org/test.owl#stime0> .
<http://www.test.org/test.owl#interval0> <http://www.test.org/test.owl#hasEndTime> <http://www.test.org/test.owl#etime0> .
<http://www.test.org/test.owl#interval0> <http://www.test.org/test.owl#hasDuration> <http://www.test.org/test.owl#duration0> .
<http://www.test.org/test.owl#stime0> <http://www.test.org/test.owl#hasValue> "525255"^^<http://www.w3.org/2001/XMLSchema#float> .
<http://www.test.org/test.owl#etime0> <http://www.test.org/test.owl#hasValue> "0"^^<http://www.w3.org/2001/XMLSchema#float> .
<http://www.test.org/test.owl#duration0> <http://www.test.org/test.owl#hasValue> "0"^^<http://www.w3.org/2001/XMLSchema#float> .
<http://www.test.org/test.owl#aduration0> <http://www.test.org/test.owl#hasValue> "0"^^<http://www.w3.org/2001/XMLSchema#float> .
<http://www.test.org/test.owl#event0> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.test.org/test.owl#ContextSwitch> .
<http://www.test.org/test.owl#event0> <http://www.test.org/test.owl#switchFrom> <http://www.test.org/test.owl#mttd0> .
<http://www.test.org/test.owl#event0> <http://www.test.org/test.owl#switchTo> <http://www.test.org/test.owl#kptrace0> .
<http://www.test.org/test.owl#trace0> <http://www.test.org/test.owl#traceContainsEvent> <http://www.test.org/test.owl#event1> .
<http://www.test.org/test.owl#event1> <http://www.test.org/test.owl#hasTime> <http://www.test.org/test.owl#interval1> .
<http://www.test.org/test.owl#event1> <http://www.test.org/test.owl#hasActiveTime> <http://www.test.org/test.owl#aduration1> .
<http://www.test.org/test.owl#interval1> <http://www.test.org/test.owl#hasStartTime> <http://www.test.org/test.owl#stime1> .
<http://www.test.org/test.owl#interval1> <http://www.test.org/test.owl#hasEndTime> <http://www.test.org/test.owl#etime1> .
<http://www.test.org/test.owl#interval1> <http://www.test.org/test.owl#hasDuration> <http://www.test.org/test.owl#duration1> .
<http://www.test.org/test.owl#stime1> <http://www.test.org/test.owl#hasValue> "525292"^^<http://www.w3.org/2001/XMLSchema#float> .
<http://www.test.org/test.owl#etime1> <http://www.test.org/test.owl#hasValue> "525306"^^<http://www.w3.org/2001/XMLSchema#float> .
<http://www.test.org/test.owl#duration1> <http://www.test.org/test.owl#hasValue> "14"^^<http://www.w3.org/2001/XMLSchema#float> .
<http://www.test.org/test.owl#aduration1> <http://www.test.org/test.owl#hasValue> "14"^^<http://www.w3.org/2001/XMLSchema#float> .
<http://www.test.org/test.owl#event1> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.test.org/test.owl#TaskRunning> .
<http://www.test.org/test.owl#event1> <http://www.test.org/test.owl#runningTask> <http://www.test.org/test.owl#kptrace0> .

thanks in advance.

Joshua Taylor · Accepted Answer · 2014-01-21T13:28:38.500

Based on this code (I'm guessing on the line numbers, but I'm pretty sure I'm right):

/* 69 */ InputStream in = this.getClass().getClassLoader().getResourceAsStream("data/nts/100.nt");
/* 70 */ traceModel.read(in, xmlbase, "N-TRIPLE");

and the beginning of the stacktrace:

java.lang.NullPointerException
    at java.io.Reader.<init>(Reader.java:78)
    at java.io.InputStreamReader.<init>(InputStreamReader.java:129)
    at com.hp.hpl.jena.util.FileUtils.asUTF8(FileUtils.java:51)
    at com.hp.hpl.jena.rdf.model.impl.NTripleReader.read(NTripleReader.java:72)
    at com.hp.hpl.jena.rdf.model.impl.ModelCom.read(ModelCom.java:226)
    …

I'd guess that in is null. Maybe that pathname needs to be "/data/nts/100.nt" (note the / at the beginning).

The stacktrace contains line numbers, and I'm pretty sure they point you to the problematic line. This is something that shouldn't be too hard to run in a debugger. Even if you can't run it in a debugger, if you're getting a null pointer exception, and you have a reference to a particular line, it's typically a good idea to check which values are used on that line and check whether they're null or not. In this case, you could just do:

InputStream in = this.getClass().getClassLoader().getResourceAsStream("data/nts/100.nt");
Objects.requireNonNull( in, "InputStream for resource data/nts/100.nt should not be null." );
traceModel.read(in, xmlbase, "N-TRIPLE");

@FopaLéonConstantin If the docs say it's "N-TRIPLE", it's probably "N-TRIPLE". I didn't check the docs before posting; it was just a secondary guess about where the NPE might have come from if the first one didn't work out. Since it could confuse readers who find this, I'll remove it from my answer. — Joshua Taylor, Jan 21 '14 at 13:28

I get trouble with java.lang.NullPointerException while loading n-triple file into a Jena SDB Model

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