code: package it.unibz.inf.ontop.query.resultset.impl;
  
  /*
   * #%L
   * ontop-reformulation-core
   * %%
   * Copyright (C) 2009 - 2014 Free University of Bozen-Bolzano
   * %%
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   * 
   *      http://www.apache.org/licenses/LICENSE-2.0
   * 
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   * #L%
   */
  
  import it.unibz.inf.ontop.answering.logging.QueryLogger;
  import it.unibz.inf.ontop.query.resultset.BooleanResultSet;
  import it.unibz.inf.ontop.exception.OntopConnectionException;
  
  import java.sql.ResultSet;
  import java.sql.SQLException;
  
  public class SQLBooleanResultSet implements BooleanResultSet {
  
      private final ResultSet set;
      private final QueryLogger queryLogger;
      private final OntopConnectionCloseable statementClosingCB;
      private boolean hasRead;
  
      public SQLBooleanResultSet(ResultSet set, QueryLogger queryLogger,
                                 OntopConnectionCloseable statementClosingCB) {
          this.set = set;
          this.queryLogger = queryLogger;
          this.statementClosingCB = statementClosingCB;
          this.hasRead = false;
      }
  
      @Override
      public void close() throws OntopConnectionException {
          try {
              if (set != null)
                  set.close();
              statementClosingCB.close();
          } catch (SQLException e) {
              queryLogger.declareConnectionException(e);
              throw new OntopConnectionException(e);
          }
      }
  
      /**
       * Returns true if there is at least one result
       */
      @Override
      public boolean getValue() throws OntopConnectionException {
          if (hasRead)
              throw new IllegalStateException("getValue() can only called once!");
          hasRead = true;
          queryLogger.declareLastResultRetrievedAndSerialize(1);
          try {
              return set.next();
          } catch (SQLException e) {
              queryLogger.declareConnectionException(e);
              throw new OntopConnectionException(e);
          }
      }
  }
  