Java tutorial
/* * Cloud9: A MapReduce Library for Hadoop * * 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 edu.umd.cloud9.collection.medline; import java.io.IOException; import java.net.URI; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.conf.Configured; import org.apache.hadoop.filecache.DistributedCache; import org.apache.hadoop.fs.FileSystem; import org.apache.hadoop.fs.Path; import org.apache.hadoop.io.IntWritable; import org.apache.hadoop.io.LongWritable; import org.apache.hadoop.io.Text; import org.apache.hadoop.mapred.FileInputFormat; import org.apache.hadoop.mapred.FileOutputFormat; import org.apache.hadoop.mapred.JobClient; import org.apache.hadoop.mapred.JobConf; import org.apache.hadoop.mapred.MapReduceBase; import org.apache.hadoop.mapred.Mapper; import org.apache.hadoop.mapred.OutputCollector; import org.apache.hadoop.mapred.Reporter; import org.apache.hadoop.util.Tool; import org.apache.hadoop.util.ToolRunner; import org.apache.log4j.Logger; import edu.umd.cloud9.collection.DocnoMapping; /** * <p> * Simple demo program that counts all the documents in a collection of MEDLINE * citations. This provides a skeleton for MapReduce programs to process the * collection. The program takes three command-line arguments: * </p> * * <ul> * <li>[input] path to the document collection * <li>[output-dir] path to the output directory * <li>[mappings-file] path to the docnos mappings file * </ul> * * <p> * Here's a sample invocation: * </p> * * <blockquote> * * <pre> * hadoop jar cloud9.jar edu.umd.cloud9.collection.medline.DemoCountMedlineCitations \ * /umd/collections/medline04.raw/ \ * /user/jimmylin/count-tmp \ * /user/jimmylin/docno.mapping * </pre> * * </blockquote> * * @author Jimmy Lin */ public class DemoCountMedlineCitations extends Configured implements Tool { private static final Logger sLogger = Logger.getLogger(DemoCountMedlineCitations.class); private static enum Count { DOCS }; private static class MyMapper extends MapReduceBase implements Mapper<LongWritable, MedlineCitation, Text, IntWritable> { private final static Text sText = new Text(); private final static IntWritable sInt = new IntWritable(1); private DocnoMapping mDocMapping; public void configure(JobConf job) { try { Path[] localFiles = DistributedCache.getLocalCacheFiles(job); // instead of hard-coding the actual concrete DocnoMapping // class, have the name of the class passed in as a property; // this makes the mapper more general mDocMapping = (DocnoMapping) Class.forName(job.get("DocnoMappingClass")).newInstance(); // simply assume that the mappings file is the only file in the // distributed cache mDocMapping.loadMapping(localFiles[0], FileSystem.getLocal(job)); } catch (Exception e) { e.printStackTrace(); throw new RuntimeException("Error initializing DocnoMapping!"); } } public void map(LongWritable key, MedlineCitation doc, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException { reporter.incrCounter(Count.DOCS, 1); sText.set(doc.getDocid()); sInt.set(mDocMapping.getDocno(doc.getDocid())); output.collect(sText, sInt); } } /** * Creates an instance of this tool. */ public DemoCountMedlineCitations() { } private static int printUsage() { System.out.println("usage: [input] [output-dir] [mappings-file]"); ToolRunner.printGenericCommandUsage(System.out); return -1; } /** * Runs this tool. */ public int run(String[] args) throws Exception { if (args.length != 3) { printUsage(); return -1; } String inputPath = args[0]; String outputPath = args[1]; String mappingFile = args[2]; sLogger.info("input: " + inputPath); sLogger.info("output dir: " + outputPath); sLogger.info("docno mapping file: " + mappingFile); JobConf conf = new JobConf(DemoCountMedlineCitations.class); conf.setJobName("DemoCountMedlineCitations"); conf.setNumReduceTasks(0); // pass in the class name as a String; this is makes the mapper general // in being able to load any collection of Indexable objects that has // docid/docno mapping specified by a DocnoMapping object conf.set("DocnoMappingClass", "edu.umd.cloud9.collection.medline.MedlineDocnoMapping"); // put the mapping file in the distributed cache so each map worker will // have it DistributedCache.addCacheFile(new URI(mappingFile), conf); FileInputFormat.setInputPaths(conf, new Path(inputPath)); FileOutputFormat.setOutputPath(conf, new Path(outputPath)); FileOutputFormat.setCompressOutput(conf, false); conf.setInputFormat(MedlineCitationInputFormat.class); conf.setOutputKeyClass(Text.class); conf.setOutputValueClass(IntWritable.class); conf.setMapperClass(MyMapper.class); // delete the output directory if it exists already FileSystem.get(conf).delete(new Path(outputPath), true); JobClient.runJob(conf); return 0; } /** * Dispatches command-line arguments to the tool via the * <code>ToolRunner</code>. */ public static void main(String[] args) throws Exception { int res = ToolRunner.run(new Configuration(), new DemoCountMedlineCitations(), args); System.exit(res); } }