TripleObjectWriter.java

/*
 * Copyright 2013, 2014 Deutsche Nationalbibliothek
 *
 * 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.culturegraph.mf.triples;

import java.io.IOException;
import java.io.Writer;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

import org.culturegraph.mf.framework.FluxCommand;
import org.culturegraph.mf.framework.MetafactureException;
import org.culturegraph.mf.framework.annotations.Description;
import org.culturegraph.mf.framework.annotations.In;
import org.culturegraph.mf.framework.annotations.Out;
import org.culturegraph.mf.framework.helpers.DefaultObjectReceiver;
import org.culturegraph.mf.framework.objects.Triple;

/**
 * Writes the object value of the triple into a file. The filename
 * is constructed from subject and predicate.
 *
 * Please note: This module does not check if the filename constructed
 * from subject and predicate stays within {@code baseDir}. THIS MODULE
 * SHOULD NOT BE USED IN ENVIRONMENTS IN WHICH THE VALUES OF SUBJECT AND
 * PREDICATE A PROVIDED BY AN UNTRUSTED SOURCE!
 *
 * @author Christoph Böhme
 */
@Description("Writes the object value of the triple into a file. The filename is "
		+ "constructed from subject and predicate. Please note: This module does "
		+ "not check if the filename constructed from subject and predicate stays "
		+ "within `baseDir`. THIS MODULE SHOULD NOT BE USED IN ENVIRONMENTS IN WHICH "
		+ "THE VALUES OF SUBJECT AND PREDICATE A PROVIDED BY AN UNTRUSTED SOURCE!")
@In(Triple.class)
@Out(Void.class)
@FluxCommand("write-triple-objects")
public final class TripleObjectWriter extends DefaultObjectReceiver<Triple> {

	private final Path baseDir;

	private Charset encoding = StandardCharsets.UTF_8;

	public TripleObjectWriter(final String baseDir) {
		this.baseDir = Paths.get(baseDir);
	}

	/**
	 * Sets the encoding used to open the resource.
	 *
	 * @param encoding
	 *            new encoding
	 */
	public void setEncoding(final String encoding) {
		this.encoding = Charset.forName(encoding);
	}

	/**
	 * Sets the encoding used to open the resource.
	 *
	 * @param encoding
	 *            new encoding
	 */
	public void setEncoding(final Charset encoding) {
		this.encoding = encoding;
	}

	/**
	 * Returns the encoding used to open the resource.
	 *
	 * @return current default setting
	 */
	public String getEncoding() {
		return encoding.name();
	}

	@Override
	public void process(final Triple triple) {
		final Path filePath = buildFilePath(triple);
		ensureParentPathExists(filePath);
		try(final Writer writer = Files.newBufferedWriter(filePath, encoding)) {
			writer.write(triple.getObject());
		} catch (final IOException e) {
			throw new MetafactureException(e);
		}
	}

	private Path buildFilePath(final Triple triple) {
		final Path file = Paths.get(triple.getSubject(), triple.getPredicate());
		return baseDir.resolve(file).toAbsolutePath().normalize();
	}

	private void ensureParentPathExists(final Path path) {
		final Path parentDir = path.getParent();
		if (parentDir != null) {
			try {
				Files.createDirectories(parentDir);
			} catch (final IOException e) {
				throw new MetafactureException(e);
			}
		}
	}

}