org.metafacture.triples.TripleObjectRetriever Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of metafacture-triples Show documentation
Modules for working with triples
The newest version!
/*
 * Copyright 2016 Christoph Böhme
 *
 * 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.
 */

package org.metafacture.triples;

import org.metafacture.commons.ResourceUtil;
import org.metafacture.framework.FluxCommand;
import org.metafacture.framework.MetafactureException;
import org.metafacture.framework.ObjectReceiver;
import org.metafacture.framework.annotations.Description;
import org.metafacture.framework.annotations.In;
import org.metafacture.framework.annotations.Out;
import org.metafacture.framework.helpers.DefaultObjectPipe;
import org.metafacture.framework.objects.Triple;
import org.metafacture.framework.objects.Triple.ObjectType;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;

/**
 * Uses the object value of the triple as a URL and emits a new triple
 * in which the object value is replaced with the contents of the resource
 * identified by the URL.
 *
 * @author Christoph Böhme
 */
@Description("Uses the object value of the triple as a URL and emits a new triple " +
    "in which the object value is replaced with the contents of the resource " +
    "identified by the URL.")
@In(Triple.class)
@Out(Triple.class)
@FluxCommand("retrieve-triple-objects")
public final class TripleObjectRetriever extends DefaultObjectPipe> {

    private Charset defaultEncoding = StandardCharsets.UTF_8;

    /**
     * Creates an instance of {@link TripleObjectRetriever}.
     */
    public TripleObjectRetriever() {
    }

    /**
     * Sets the default encoding to use when no encoding is
     * provided by the server. The default setting is UTF-8.
     *
     * @param defaultEncoding new default encoding
     */
    public void setDefaultEncoding(final String defaultEncoding) {
        this.defaultEncoding = Charset.forName(defaultEncoding);
    }

    /**
     * Sets the default encoding to use when no encoding is
     * provided by the server. The default setting is UTF-8.
     *
     * @param defaultEncoding new default encoding
     */
    public void setDefaultEncoding(final Charset defaultEncoding) {
        this.defaultEncoding = defaultEncoding;
    }

    /**
     * Returns the default encoding used when no encoding is
     * provided by the server. The default setting is UTF-8.
     *
     * @return current default setting
     */
    public String getDefaultEncoding() {
        return defaultEncoding.name();
    }

    @Override
    public void process(final Triple triple) {
        assert !isClosed();
        if (triple.getObjectType() != ObjectType.STRING) {
            return;
        }
        final String objectValue = retrieveObjectValue(triple.getObject());
        getReceiver().process(new Triple(triple.getSubject(), triple.getPredicate(),
                objectValue));
    }

    private String retrieveObjectValue(final String urlString) {
        try {
            final URL url = new URL(urlString);
            final URLConnection connection = url.openConnection();
            connection.connect();
            final String encodingName = connection.getContentEncoding();
            final Charset encoding = encodingName != null ? Charset.forName(encodingName) : defaultEncoding;
            try (InputStream inputStream = connection.getInputStream()) {
                return ResourceUtil.readAll(inputStream, encoding);
            }
        }
        catch (final IOException e) {
            throw new MetafactureException(e);
        }
    }

}