TestSparqlRepository.java

package de.naturzukunft.rdf4j.sparql.spring.controller;

import org.eclipse.rdf4j.query.TupleQuery;
import org.eclipse.rdf4j.query.TupleQueryResult;
import org.eclipse.rdf4j.repository.RepositoryConnection;
import org.eclipse.rdf4j.repository.sparql.SPARQLRepository;

public class TestSparqlRepository {
	public static void main(String[] args) {
		String query = "select distinct ?Concept where {[] a ?Concept} LIMIT 100";
		String url = "https://dbpedia.org/sparql";
		SPARQLRepository repo = new SPARQLRepository(url);
		TupleQueryResult result = null;
		try (RepositoryConnection conn = repo.getConnection()) {
			TupleQuery tupleQuery = conn.prepareTupleQuery(query);
			result = tupleQuery.evaluate();
		}
		int count = 0;
		while (result.hasNext()) {
			System.out.println(result.next());
			result.next();
			count++;
		}
		System.out.println(count);
	}
}

There's a couple of things wrong with this.

1. you're calling result.next() twice in the loop, which will lead to skipping half of your results
2. you're iterating over the result iteration outside the try-with-resources block. That means the connection has been closed and you won't get any results.

Simple fix:

	public static void main(String[] args) throws Exception {
		String query = "select distinct ?Concept where {[] a ?Concept} LIMIT 100";
		String url = "http://dbpedia.org/sparql";
		SPARQLRepository repo = new SPARQLRepository(url);
		try (RepositoryConnection conn = repo.getConnection()) {
			TupleQuery tupleQuery = conn.prepareTupleQuery(query);
			TupleQueryResult result = tupleQuery.evaluate();
			int count = 0;
			while (result.hasNext()) {
				System.out.println(result.next());
				count++;
			}
			System.out.println(count);
		}
	}

Btw using hasNext()/next() can lead to mistakes (as in your example). Easier is to use a for-each loop instead of a while loop:

for(BindingSet bs: result) {
   System.out.println(bs);
   count++;
}

Alternatively, if you want to keep track of the result outside the block, materialize the result iterator to a List:

	public static void main(String[] args) throws Exception {
		String query = "select distinct ?Concept where {[] a ?Concept} LIMIT 100";
		String url = "http://dbpedia.org/sparql";
		SPARQLRepository repo = new SPARQLRepository(url);
                List<BindingSet> result = null;
		try (RepositoryConnection conn = repo.getConnection()) {
			TupleQuery tupleQuery = conn.prepareTupleQuery(query);
			result = QueryResults.asList(tupleQuery.evaluate());
		}
                result.forEach(System.out::println);
                System.out.println(result.size());
	}