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.trec; import java.io.IOException; import java.net.URI; import java.util.Arrays; import org.apache.commons.cli.CommandLine; import org.apache.commons.cli.CommandLineParser; import org.apache.commons.cli.GnuParser; import org.apache.commons.cli.HelpFormatter; import org.apache.commons.cli.OptionBuilder; import org.apache.commons.cli.Options; import org.apache.commons.cli.ParseException; 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.mapreduce.Counters; import org.apache.hadoop.mapreduce.Job; import org.apache.hadoop.mapreduce.Mapper; import org.apache.hadoop.mapreduce.lib.input.FileInputFormat; import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat; import org.apache.hadoop.util.Tool; import org.apache.hadoop.util.ToolRunner; import org.apache.log4j.Logger; import edu.umd.cloud9.collection.DocnoMapping; /** * Simple demo program that counts all the documents in the TREC collection. Run without any * arguments for help. The guava jar must be included using {@code -libjar}. * * @author Jimmy Lin */ public class DemoCountTrecDocuments extends Configured implements Tool { private static final Logger LOG = Logger.getLogger(DemoCountTrecDocuments.class); private static enum Count { DOCS }; private static class MyMapper extends Mapper<LongWritable, TrecDocument, Text, IntWritable> { private static final Text docid = new Text(); private static final IntWritable one = new IntWritable(1); private DocnoMapping docMapping; @Override public void setup(Context context) { try { Configuration conf = context.getConfiguration(); Path[] localFiles = DistributedCache.getLocalCacheFiles(conf); // 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. docMapping = (DocnoMapping) Class.forName(conf.get("DocnoMappingClass")).newInstance(); // Simply assume that the mappings file is the only file in the distributed cache. docMapping.loadMapping(localFiles[0], FileSystem.getLocal(conf)); } catch (Exception e) { e.printStackTrace(); throw new RuntimeException("Error initializing DocnoMapping!"); } } @Override public void map(LongWritable key, TrecDocument doc, Context context) throws IOException, InterruptedException { context.getCounter(Count.DOCS).increment(1); docid.set(doc.getDocid()); one.set(docMapping.getDocno(doc.getDocid())); context.write(docid, one); } } /** * Creates an instance of this tool. */ public DemoCountTrecDocuments() { } public static final String COLLECTION_OPTION = "collection"; public static final String OUTPUT_OPTION = "output"; public static final String MAPPING_OPTION = "docnoMapping"; /** * Runs this tool. */ @SuppressWarnings("static-access") public int run(String[] args) throws Exception { Options options = new Options(); options.addOption(OptionBuilder.withArgName("path").hasArg().withDescription("(required) collection path") .create(COLLECTION_OPTION)); options.addOption(OptionBuilder.withArgName("path").hasArg().withDescription("(required) output path") .create(OUTPUT_OPTION)); options.addOption(OptionBuilder.withArgName("path").hasArg().withDescription("(required) DocnoMapping data") .create(MAPPING_OPTION)); CommandLine cmdline; CommandLineParser parser = new GnuParser(); try { cmdline = parser.parse(options, args); } catch (ParseException exp) { System.err.println("Error parsing command line: " + exp.getMessage()); return -1; } if (!cmdline.hasOption(COLLECTION_OPTION) || !cmdline.hasOption(OUTPUT_OPTION) || !cmdline.hasOption(MAPPING_OPTION)) { HelpFormatter formatter = new HelpFormatter(); formatter.printHelp(this.getClass().getName(), options); ToolRunner.printGenericCommandUsage(System.out); return -1; } String inputPath = cmdline.getOptionValue(COLLECTION_OPTION); String outputPath = cmdline.getOptionValue(OUTPUT_OPTION); String mappingFile = cmdline.getOptionValue(MAPPING_OPTION); LOG.info("Tool: " + DemoCountTrecDocuments.class.getCanonicalName()); LOG.info(" - input: " + inputPath); LOG.info(" - output dir: " + outputPath); LOG.info(" - docno mapping file: " + mappingFile); Job job = new Job(getConf(), DemoCountTrecDocuments.class.getSimpleName()); job.setJarByClass(DemoCountTrecDocuments.class); job.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. job.getConfiguration().set("DocnoMappingClass", TrecDocnoMapping.class.getCanonicalName()); // Put the mapping file in the distributed cache so each map worker will have it. DistributedCache.addCacheFile(new URI(mappingFile), job.getConfiguration()); FileInputFormat.setInputPaths(job, new Path(inputPath)); FileOutputFormat.setOutputPath(job, new Path(outputPath)); FileOutputFormat.setCompressOutput(job, false); job.setInputFormatClass(TrecDocumentInputFormat.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); job.setMapperClass(MyMapper.class); // Delete the output directory if it exists already. FileSystem.get(job.getConfiguration()).delete(new Path(outputPath), true); job.waitForCompletion(true); Counters counters = job.getCounters(); int numDocs = (int) counters.findCounter(Count.DOCS).getValue(); LOG.info("Read " + numDocs + " docs."); return 0; } /** * Dispatches command-line arguments to the tool via the {@code ToolRunner}. */ public static void main(String[] args) throws Exception { LOG.info("Running " + DemoCountTrecDocuments.class.getCanonicalName() + " with args " + Arrays.toString(args)); ToolRunner.run(new Configuration(), new DemoCountTrecDocuments(), args); } }