norbert.mynemo.dataimport.fileformat.input.MovieLensIdConverter.java Source code

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Here is the source code for norbert.mynemo.dataimport.fileformat.input.MovieLensIdConverter.java

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/*
 * Copyright 2015 Norbert
 *
 * 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 norbert.mynemo.dataimport.fileformat.input;

import static com.google.common.base.Preconditions.checkArgument;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVParser;
import org.apache.commons.csv.CSVRecord;

/**
 * This class provides a conversion from the MovieLens ids of movies to the IMDb ids. This
 * information is extracted from a file that can be exported from the MovieLens web site.
 */
class MovieLensIdConverter {

    private static final int IMDB_MOVIE_ID_INDEX = 3;
    private static final int MOVIELENS_MOVIE_ID_INDEX = 0;
    private static final int RECORD_SIZE = 5;
    /**
     * A map containing a MovieLens id as key, and its corresponding IMDb id as value.
     */
    private final Map<String, String> mappings;

    /**
     * Loads the mapping file.
     *
     * <p>
     * The columns of the mapping file are:
     * <ol>
     * <li>MovieLens id of the movie</li>
     * <li>rating</li>
     * <li>average</li>
     * <li>IMDb id of the movie</li>
     * <li>title and year</li>
     * </ol>
     *
     * @param mappingFilepath the file that contains the mapping
     */
    public MovieLensIdConverter(String mappingFilepath) throws IOException {
        checkArgument(new File(mappingFilepath).exists(), "The mapping file must exist.");

        CSVParser parser = new CSVParser(
                new CleanRatingsReader(new BufferedReader(new FileReader(mappingFilepath))), CSVFormat.MYSQL);

        mappings = new HashMap<>();
        for (CSVRecord record : parser) {
            if (record.size() != RECORD_SIZE) {
                parser.close();
                throw new IllegalStateException("Error: unable to parse the movie file \"" + mappingFilepath
                        + "\". A list of five tab separated values is expected. Approximate" + " line number: "
                        + record.getRecordNumber());
            }
            mappings.put(record.get(MOVIELENS_MOVIE_ID_INDEX), record.get(IMDB_MOVIE_ID_INDEX));
        }

        parser.close();
    }

    /**
     * Returns <code>true</code> if a corresponding IMDb movie id exists. Returns <code>false</code>
     * otherwise.
     *
     * @param movielensId an id of a movie from MovieLens
     */
    public boolean canConvert(String movielensId) {
        return mappings.containsKey(movielensId);
    }

    /**
     * Removes all known mappings. The converter won't be able to convert any id after this call
     * returns.
     */
    public void clear() {
        mappings.clear();
    }

    /**
     * Returns the corresponding IMDb id of the given MovieLens id of a movie.
     *
     * @param movielensId an id of a movie from MovieLens
     * @return the corresponding IMDb id
     * @throws IllegalArgumentException if {@code movielensId} has no corresponding IMDb id.
     */
    public String convert(String movielensId) {
        checkArgument(mappings.containsKey(movielensId),
                "The MovieLens id of a movie must have a" + " corresponding imdb id.");

        return mappings.get(movielensId);
    }
}