de.tudarmstadt.ukp.jwktl.api.entry.BerkeleyDBWiktionaryIterator Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of dkpro-jwktl Show documentation

JWKTL (Java Wiktionary Library) is a Java-based API that enables efficient and structured access to the information encoded in the English and the German Wiktionary edition, including sense definitions, part of speech tags, etymology, example sentences, translations, semantic relations and many other lexical information types.

The newest version!

/*******************************************************************************
 * Copyright 2013
 * Ubiquitous Knowledge Processing (UKP) Lab
 * Technische Universität Darmstadt
 * 
 * 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 de.tudarmstadt.ukp.jwktl.api.entry;

import com.sleepycat.je.DatabaseException;
import com.sleepycat.persist.EntityCursor;

import de.tudarmstadt.ukp.jwktl.api.WiktionaryException;
import de.tudarmstadt.ukp.jwktl.api.util.WiktionaryIterator;

/**
 * Implementation of the {@link WiktionaryIterator} for the use of a
 * Berkeley DB {@link EntityCursor} as a source of elements. The cursor
 * is passed to the constructor and automatically closed upon manually
 * termination of the iteration or after all elements have been traversed.
 * Additionally, a hotspot is provided to react on the return of an
 * element of the cursor to, e.g., initialize the entity. It is
 * possible to convert the stored entity to a more general type
 * using different type parameters.
 * @param  the class type that is returned for each
 *     fetched element.
 * @param  the class type the stored entities have. It
 *     is necessary that the input type is the same or a subclass
 *     of the type specified as output.
 */
public class BerkeleyDBWiktionaryIterator 
		extends WiktionaryIterator {

	protected BerkeleyDBWiktionaryEdition edition;
	protected EntityCursor cursor;

	/** Initializes the iterator for the specified cursor. */
	public BerkeleyDBWiktionaryIterator(final BerkeleyDBWiktionaryEdition edition,
			final EntityCursor cursor) {
		this.edition = edition;
		this.cursor = cursor;
		edition.openCursors.add(cursor);
	}

	protected OutputType fetchNext() {
		try {
			if (closed)
				return null;

			do {
				InputType next = cursor.next();
				if (next == null)
					return null;

				OutputType result = loadEntity(next);
				if (result != null)
					return result;
			} while (true);

			//return loadEntity(cursor.next());
		} catch (DatabaseException e) {
			throw new WiktionaryException(e);
		}
	}

	/** Hotspot that is invoked when returning an entity. It can, e.g.,
	 *  be used to initialize the entity before usage. */
	protected OutputType loadEntity(final InputType entity) {
		return entity;
	}

	protected void doClose() {
		try {
			cursor.close();
			edition.openCursors.remove(cursor);
		} catch (DatabaseException e) {
			throw new WiktionaryException(e);
		}
	}

}