001/**
002 * Copyright (c) 2011, The University of Southampton and the individual contributors.
003 * All rights reserved.
004 *
005 * Redistribution and use in source and binary forms, with or without modification,
006 * are permitted provided that the following conditions are met:
007 *
008 *   *  Redistributions of source code must retain the above copyright notice,
009 *      this list of conditions and the following disclaimer.
010 *
011 *   *  Redistributions in binary form must reproduce the above copyright notice,
012 *      this list of conditions and the following disclaimer in the documentation
013 *      and/or other materials provided with the distribution.
014 *
015 *   *  Neither the name of the University of Southampton nor the names of its
016 *      contributors may be used to endorse or promote products derived from this
017 *      software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
020 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
021 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
022 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
023 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
026 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
028 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package org.openimaj.hadoop.sequencefile;
031
032import java.util.ArrayList;
033import java.util.List;
034import java.util.Map;
035import java.util.Map.Entry;
036
037import org.apache.hadoop.conf.Configuration;
038import org.apache.hadoop.io.SequenceFile;
039import org.apache.hadoop.io.SequenceFile.Metadata;
040import org.apache.hadoop.io.Text;
041import org.apache.hadoop.util.Tool;
042
043/**
044 * Utility functions for storing and retrieving metadata to be stored in a
045 * {@link SequenceFile} by the {@link MetadataSequenceFileOutputFormat}.
046 * <p>
047 * Standard usage would be to use the {@link #setMetadata(Map, Configuration)}
048 * method to add the given metadata to the {@link Configuration} in the part of
049 * the code that runs locally (i.e. in a {@link Tool#run(String[])} method). The
050 * configuration would then be distributed across the cluster, and any mappers
051 * or reducers that use the {@link MetadataSequenceFileOutputFormat} will
052 * automatically have the metadata added to their output file(s).
053 *
054 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
055 *
056 */
057public class MetadataConfiguration {
058        private static final String META_PREFIX = "org.openimaj.hadoop.sequencefile.metadata.";
059        private static final String META_KEYS = META_PREFIX + "__metadataKeys__";
060
061        /**
062         * Standard key for a unique identifier metadata item
063         */
064        public static final String UUID_KEY = "UUID";
065
066        /**
067         * Standard key for a comment metadata item
068         */
069        public static final String COMMENT_KEY = "Comment";
070
071        /**
072         * Standard key for a storing an indicator of the mime-type of the value
073         * fields
074         */
075        public static final String CONTENT_TYPE_KEY = "ContentType";
076
077        private MetadataConfiguration() {
078        }
079
080        /**
081         * Read any metadata stored in the {@link Configuration}.
082         *
083         * @param conf
084         *            the configuration
085         * @return the metadata map
086         */
087        public static Metadata getMetadata(Configuration conf) {
088                final Metadata metadata = new Metadata();
089
090                final String[] keys = conf.getStrings(META_KEYS);
091
092                if (keys != null) {
093                        for (final String key : keys) {
094                                final String value = conf.get(META_PREFIX + key);
095
096                                if (value != null)
097                                        metadata.set(new Text(key), new Text(value));
098                        }
099                }
100
101                return metadata;
102        }
103
104        /**
105         * Write the given metadata to the {@link Configuration}.
106         *
107         * @param metadata
108         *            the metadata.
109         * @param conf
110         *            the configuration.
111         */
112        public static void setMetadata(Map<String, String> metadata, Configuration conf) {
113                for (final Entry<String, String> entry : metadata.entrySet()) {
114                        conf.set(META_PREFIX + entry.getKey(), entry.getValue());
115                }
116
117                final List<String> keys = new ArrayList<String>();
118                if (conf.getStringCollection(META_KEYS) != null)
119                        keys.addAll(conf.getStringCollection(META_KEYS));
120
121                for (final String key : metadata.keySet()) {
122                        keys.add(key);
123                }
124
125                conf.setStrings(META_KEYS, keys.toArray(new String[keys.size()]));
126        }
127
128}