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ARQ is a SPARQL 1.1 query engine for Apache Jena
There is a newer version: 5.1.0
/**
 * 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.resultset;

import static org.apache.jena.riot.resultset.ResultSetLang.*;

import java.io.InputStream ;
import java.io.Reader ;
import java.util.HashMap ;
import java.util.Map ;
import java.util.Objects ;

import org.apache.jena.atlas.lib.NotImplemented ;
import org.apache.jena.query.ResultSet ;
import org.apache.jena.riot.Lang ;
import org.apache.jena.riot.RiotException ;
import org.apache.jena.riot.resultset.rw.ResultSetReaderJSON;
import org.apache.jena.riot.resultset.rw.ResultSetReaderThrift;
import org.apache.jena.riot.resultset.rw.ResultSetReaderXML;
import org.apache.jena.riot.thrift.BinRDF ;
import org.apache.jena.sparql.resultset.CSVInput ;
import org.apache.jena.sparql.resultset.SPARQLResult;
import org.apache.jena.sparql.resultset.TSVInput ;
import org.apache.jena.sparql.util.Context ;

public class ResultSetReaderRegistry {
    
    /** Lookup a {@link Lang} to get the registered {@link ResultSetReaderFactory} (or null) */
    public static ResultSetReaderFactory getFactory(Lang lang) {
        Objects.requireNonNull(lang) ;
        return registry.get(lang) ;
    }

    /** Register a {@link ResultSetReaderFactory} for a {@link Lang} */
    public static void register(Lang lang, ResultSetReaderFactory factory) {
        Objects.requireNonNull(lang) ;
        Objects.requireNonNull(factory) ;
        registry.put(lang, factory) ;
    }

    /** Test whether {@link Lang} is registered as a result set syntax. */
    public static boolean isRegistered(Lang lang) {
        Objects.requireNonNull(lang) ;
        return registry.containsKey(lang);
    }

    private static Map registry = new HashMap<>() ;
    
    private static boolean initialized = false ;
    public static void init() {
        if ( initialized )
            return ;
        initialized = true ;

        ResultSetReaderFactory factory = new ResultSetReaderFactoryStd() ;
        register(SPARQLResultSetXML,    ResultSetReaderXML.factory) ;
        register(SPARQLResultSetJSON,   ResultSetReaderJSON.factory) ;
        register(SPARQLResultSetThrift, ResultSetReaderThrift.factory) ;
        register(SPARQLResultSetCSV,    factory) ;
        register(SPARQLResultSetTSV,    factory) ;
    }
    
    private static class ResultSetReaderFactoryStd implements ResultSetReaderFactory {
        @Override
        public ResultSetReader create(Lang lang) {
            lang = Objects.requireNonNull(lang, "Language must not be null") ;
//            if ( lang.equals(SPARQLResultSetXML) )      return readerXML ;
//            if ( lang.equals(SPARQLResultSetJSON) )     return readerJSON ;
            if ( lang.equals(SPARQLResultSetCSV) )      return readerCSV ;
            if ( lang.equals(SPARQLResultSetTSV) )      return readerTSV ;
            throw new RiotException("Lang not registered (ResultSet reader)") ;
        }
    }
    
    private static class ResultSetReaderThriftFactory implements ResultSetReaderFactory {
        @Override
        public ResultSetReader create(Lang lang) {
            return new ResultSetReader() {
                @Override
                public ResultSet read(InputStream in, Context context) {
                    return BinRDF.readResultSet(in) ;
                }
                @Override
                public ResultSet read(Reader in, Context context) {
                    throw new NotImplemented("Reading binary data from a java.io.Reader is not possible") ;
                    
                }
                @Override public SPARQLResult readAny(InputStream in, Context context) { 
                    return new SPARQLResult(read(in, context));
                }    
            } ;
        }
    }
    // These all call static methods, so have no state and so don't
    // need to be created for each read operation.  
    
//    private static ResultSetReader readerXML = new ResultSetReader() {
//        @Override public ResultSet read(InputStream in, Context context)    { return XMLInput.fromXML(in); }
//        @Override public ResultSet read(Reader in, Context context)         { return XMLInput.fromXML(in); }
//        @Override public SPARQLResult readAny(InputStream in, Context context) { return XMLInput.make(in); }
//    };

//    private static ResultSetReader readerJSON = new ResultSetReader() {
//        @Override public ResultSet read(InputStream in, Context context)    { return JSONInput.fromJSON(in) ; }
//        @Override public ResultSet read(Reader in, Context context)         { throw new NotImplemented("Reader") ; } 
//    } ;
//
    private static ResultSetReader readerCSV = new ResultSetReader() {
        @Override public ResultSet read(InputStream in, Context context)    { return CSVInput.fromCSV(in) ; }
        @Override public ResultSet read(Reader in, Context context)         { throw new NotImplemented("Reader") ; } 
        @Override public SPARQLResult readAny(InputStream in, Context context) {
            // Not switchable.
            return new SPARQLResult(read(in, context));
        } 
    } ;
    
    private static ResultSetReader readerTSV = new ResultSetReader() {
        @Override public ResultSet read(InputStream in, Context context)    { return TSVInput.fromTSV(in); }
        @Override public ResultSet read(Reader in, Context context)         { throw new NotImplemented("Reader") ; } 
        @Override public SPARQLResult readAny(InputStream in, Context context) {
            // Not switchable.
            return new SPARQLResult(read(in, context));
        } 
    } ;

    private static ResultSetReader readerNo = new ResultSetReader() {
        @Override public ResultSet read(InputStream in, Context context)    { return null ; }
        @Override public ResultSet read(Reader in, Context context)         { return null ; }
        @Override public SPARQLResult readAny(InputStream in, Context context) { return null ; }
    } ;
}