SortingRDFHandler.java

/*
 * *********************************************************************************************************************
 *
 * blueMarine II: Semantic Media Centre
 * http://tidalwave.it/projects/bluemarine2
 *
 * Copyright (C) 2015 - 2021 by Tidalwave s.a.s. (http://tidalwave.it)
 *
 * *********************************************************************************************************************
 *
 * 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.
 *
 * *********************************************************************************************************************
 *
 * git clone https://bitbucket.org/tidalwave/bluemarine2-src
 * git clone https://github.com/tidalwave-it/bluemarine2-src
 *
 * *********************************************************************************************************************
 */
package it.tidalwave.bluemarine2.util;

import javax.annotation.Nonnull;
import java.util.ArrayList;
import java.util.List;
import lombok.experimental.Delegate;
import lombok.RequiredArgsConstructor;
import org.eclipse.rdf4j.model.Statement;
import org.eclipse.rdf4j.model.vocabulary.RDF;
import org.eclipse.rdf4j.rio.RDFHandler;
import org.eclipse.rdf4j.rio.RDFHandlerException;

/***********************************************************************************************************************
 *
 * @author  Fabrizio Giudici
 *
 **********************************************************************************************************************/
@RequiredArgsConstructor
public class SortingRDFHandler implements RDFHandler
  {
    interface Exclusions
      {
        public void handleStatement (Statement statement)
          throws RDFHandlerException;

        public void endRDF()
          throws RDFHandlerException;
      }

    @Nonnull @Delegate(excludes = Exclusions.class)
    private final RDFHandler delegate;

    private final List<Statement> statements = new ArrayList<>();

    @Override
    public void handleStatement (@Nonnull final Statement statement)
      throws RDFHandlerException
      {
        statements.add(statement);
      }

    @Override
    public void endRDF()
      throws RDFHandlerException
      {
        statements.sort((st1, st2) ->
          {
            final String s1 = st1.getSubject().stringValue();
            final String s2 = st2.getSubject().stringValue();
            final int c1 = s1.compareTo(s2);

            if (c1 != 0)
              {
                return c1;
              }

            final String p1 = st1.getPredicate().stringValue();
            final String p2 = st2.getPredicate().stringValue();
            final int c2 = p1.compareTo(p2);

            if (c2 != 0)
              {
                if (p1.equals(RDF.TYPE.stringValue()))
                  {
                    return -1;
                  }
                else if (p2.equals(RDF.TYPE.stringValue()))
                  {
                    return +1;
                  }

                return c2;
              }

            final String o1 = st1.getObject().stringValue();
            final String o2 = st2.getObject().stringValue();

            return o1.compareTo(o2);
          });

        for (final Statement statement : statements)
          {
            delegate.handleStatement(statement);
          }

        delegate.endRDF();
      }
  }