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.Text;
040import org.apache.hadoop.io.SequenceFile.Metadata;
041import org.apache.hadoop.util.Tool;
042
043/**
044 * Utility functions for storing and retrieving metadata
045 * to be stored in a {@link SequenceFile} by the  
046 * {@link MetadataSequenceFileOutputFormat}. 
047 * <p>
048 * Standard usage would be to use the {@link #setMetadata(Map, Configuration)}
049 * method to add the given metadata to the {@link Configuration} in the
050 * part of the code that runs locally (i.e. in a {@link Tool#run(String[])} method).
051 * The configuration would then be distributed across the cluster, and any
052 * mappers or reducers that use the {@link MetadataSequenceFileOutputFormat}
053 * will automatically have the metadata added to their output file(s).
054 * 
055 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
056 *
057 */
058public class MetadataConfiguration {
059        private static final String META_PREFIX = "org.openimaj.hadoop.sequencefile.metadata.";
060        private static final String META_KEYS = META_PREFIX + "__metadataKeys__"; 
061
062        /**
063         * Standard key for a unique identifier metadata item
064         */
065        public static final String UUID_KEY = "UUID";
066        
067        /**
068         * Standard key for a comment metadata item 
069         */
070        public static final String COMMENT_KEY = "Comment";
071        
072        /**
073         * Standard key for a storing an indicator of the mime-type of the value fields 
074         */
075        public static final String CONTENT_TYPE_KEY = "ContentType";
076
077        private MetadataConfiguration() {}
078        
079        /**
080         * Read any metadata stored in the {@link Configuration}.
081         * 
082         * @param conf the configuration
083         * @return the metadata map
084         */
085        public static Metadata getMetadata(Configuration conf) {
086                Metadata metadata = new Metadata();
087
088                String [] keys = conf.getStrings(META_KEYS);
089
090                if (keys != null) {
091                        for (String key : keys) {
092                                String value = conf.get(META_PREFIX + key);
093
094                                if (value != null)
095                                        metadata.set(new Text(key), new Text(value));
096                        }
097                }
098
099                return metadata;
100        }
101
102        /**
103         * Write the given metadata to the {@link Configuration}.
104         * 
105         * @param metadata the metadata.
106         * @param conf the configuration.
107         */
108        public static void setMetadata(Map<String, String> metadata, Configuration conf) {
109                for (Entry<String, String> entry : metadata.entrySet()) {
110                        conf.set(META_PREFIX + entry.getKey(), entry.getValue());
111                }
112
113                List<String> keys = new ArrayList<String>();
114                if (conf.getStringCollection(META_KEYS) != null)
115                        keys.addAll(conf.getStringCollection(META_KEYS));
116
117                for (String key : metadata.keySet()) {
118                        keys.add(key);
119                }
120
121                conf.setStrings(META_KEYS, keys.toArray(new String[keys.size()]));
122        }
123
124}