jena-arq/src/main/java/org/apache/jena/riot/writer/WriterStreamRDFBase.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 */

package org.apache.jena.riot.writer;

import java.io.BufferedWriter ;
import java.io.OutputStream ;
import java.io.Writer ;

import org.apache.jena.atlas.io.IndentedWriter ;
import org.apache.jena.graph.Node ;
import org.apache.jena.graph.Triple ;
import org.apache.jena.riot.RIOT;
import org.apache.jena.riot.out.NodeFormatterTTL ;
import org.apache.jena.riot.out.NodeToLabel ;
import org.apache.jena.riot.system.PrefixMap ;
import org.apache.jena.riot.system.PrefixMapFactory ;
import org.apache.jena.riot.system.RiotLib ;
import org.apache.jena.riot.system.StreamRDF ;
import org.apache.jena.sparql.core.Quad ;
import org.apache.jena.sparql.util.Context;

/** Core engine for output of triples / quads that is streaming.
 *  Handles prefixes and base, together with the environment for processing.
 *  If fed quads, the output is valid TriG.
 *  If fed only triples, the output is valid Turtle.
 *  Not for N-Quads and N-triples.
 */

public abstract class WriterStreamRDFBase implements StreamRDF
{
    // What did we do last?
    protected boolean activeTripleData  = false ;
    protected boolean activeQuadData    = false ;
    protected boolean lastWasDirective  = false ;

    protected final PrefixMap pMap ;
    protected String baseURI = null ;
    protected final NodeToLabel nodeToLabel ;

    protected NodeFormatterTTL fmt ;
    protected final IndentedWriter out ;
    protected final DirectiveStyle prefixStyle;
    protected final boolean printBase;

    public WriterStreamRDFBase(OutputStream output, Context context) {
        this(new IndentedWriter(output), context) ;
    }

    public WriterStreamRDFBase(Writer output, Context context) {
        this(wrap(output), context);
    }

    public WriterStreamRDFBase(IndentedWriter output, Context context) {
        out = output ;
        pMap = PrefixMapFactory.create() ;
        nodeToLabel = NodeToLabel.createScopeByDocument() ;
        
        // Stream writing does not take an external base URI from the API "write"
        // call. The base URI is output if StreamRDF.base() called, which means BASE
        // was in the data stream.
        baseURI = null ;
        prefixStyle = WriterLib.directiveStyle(context);
        printBase = 
            ( context == null ) ? true : context.isFalseOrUndef(RIOT.symTurtleOmitBase);
        setFormatter() ;
    }

    private void setFormatter() {
        fmt = new NodeFormatterTTL(baseURI, pMap, nodeToLabel);
    }

    private static IndentedWriter wrap(Writer output) {
        if ( !(output instanceof BufferedWriter) )
            output = new BufferedWriter(output, 32 * 1024);
        return RiotLib.create(output);
    }

    private void reset$() {
        activeTripleData = false;
        activeQuadData = false;
        lastWasDirective = false;
    }

    @Override
    public final void start() {
        reset$();
        startData();
    }

    @Override
    public final void finish() {
        endData();
        out.flush();
    }

    @Override
    public final void triple(Triple triple) {
        print(triple);
        activeTripleData = true;
    }

    @Override
    public final void quad(Quad quad) {
        print(quad);
        activeQuadData = true;
    }

    @Override
    public final void base(String base) {
        baseURI = base;
        lastWasDirective = true;
        setFormatter();
        if ( printBase )
            RiotLib.writeBase(out, base, prefixStyle == DirectiveStyle.SPARQL);
    }

    @Override
    public final void prefix(String prefix, String iri) {
        endData();
        lastWasDirective = true;
        pMap.add(prefix, iri);
        RiotLib.writePrefix(out, prefix, iri, prefixStyle == DirectiveStyle.SPARQL);
    }

    protected void outputNode(Node n) {
        fmt.format(out, n);
    }

    // Subclass contract

    protected abstract void startData();

    protected abstract void endData();

    protected abstract void print(Quad quad);

    protected abstract void print(Triple triple);

    protected abstract void reset();
}