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 code; import java.io.IOException; import java.util.Iterator; import java.util.StringTokenizer; 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.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.Job; import org.apache.hadoop.mapreduce.Mapper; import org.apache.hadoop.mapreduce.Reducer; 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 cern.colt.Arrays; /** * Simple word count demo. * * @author Jimmy Lin */ public class DemoWordCount extends Configured implements Tool { private static final Logger LOG = Logger.getLogger(DemoWordCount.class); // Mapper: emits (token, 1) for every word occurrence. private static class MyMapper extends Mapper<LongWritable, Text, Text, IntWritable> { // Reuse objects to save overhead of object creation. private final static IntWritable ONE = new IntWritable(1); private final static Text WORD = new Text(); @Override public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException { String line = ((Text) value).toString(); StringTokenizer itr = new StringTokenizer(line); String tokenStr = ""; while (itr.hasMoreTokens()) { tokenStr = itr.nextToken(); if (tokenStr.matches("[A-Za-z]+")) { WORD.set(tokenStr); //WORD.set(itr.nextToken()); context.write(WORD, ONE); } } } } // Reducer: sums up all the counts. private static class MyReducer extends Reducer<Text, IntWritable, Text, IntWritable> { // Reuse objects. private final static IntWritable SUM = new IntWritable(); @Override public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException { // Sum up values. Iterator<IntWritable> iter = values.iterator(); int sum = 0; while (iter.hasNext()) { sum += iter.next().get(); } SUM.set(sum); context.write(key, SUM); } } /** * Creates an instance of this tool. */ public DemoWordCount() { } private static final String INPUT = "input"; private static final String OUTPUT = "output"; private static final String NUM_REDUCERS = "numReducers"; /** * Runs this tool. */ @SuppressWarnings({ "static-access" }) public int run(String[] args) throws Exception { Options options = new Options(); options.addOption(OptionBuilder.withArgName("path").hasArg().withDescription("input path").create(INPUT)); options.addOption(OptionBuilder.withArgName("path").hasArg().withDescription("output path").create(OUTPUT)); options.addOption(OptionBuilder.withArgName("num").hasArg().withDescription("number of reducers") .create(NUM_REDUCERS)); 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(INPUT) || !cmdline.hasOption(OUTPUT)) { System.out.println("args: " + Arrays.toString(args)); HelpFormatter formatter = new HelpFormatter(); formatter.setWidth(120); formatter.printHelp(this.getClass().getName(), options); ToolRunner.printGenericCommandUsage(System.out); return -1; } String inputPath = cmdline.getOptionValue(INPUT); String outputPath = cmdline.getOptionValue(OUTPUT); int reduceTasks = cmdline.hasOption(NUM_REDUCERS) ? Integer.parseInt(cmdline.getOptionValue(NUM_REDUCERS)) : 1; LOG.info("Tool: " + DemoWordCount.class.getSimpleName()); LOG.info(" - input path: " + inputPath); LOG.info(" - output path: " + outputPath); LOG.info(" - number of reducers: " + reduceTasks); Configuration conf = getConf(); Job job = Job.getInstance(conf); job.setJobName(DemoWordCount.class.getSimpleName()); job.setJarByClass(DemoWordCount.class); job.setNumReduceTasks(reduceTasks); FileInputFormat.setInputPaths(job, new Path(inputPath)); FileOutputFormat.setOutputPath(job, new Path(outputPath)); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); job.setMapperClass(MyMapper.class); job.setCombinerClass(MyReducer.class); job.setReducerClass(MyReducer.class); // Delete the output directory if it exists already. Path outputDir = new Path(outputPath); FileSystem.get(conf).delete(outputDir, true); long startTime = System.currentTimeMillis(); job.waitForCompletion(true); LOG.info("Job Finished in " + (System.currentTimeMillis() - startTime) / 1000.0 + " seconds"); return 0; } /** * Dispatches command-line arguments to the tool via the {@code ToolRunner}. */ public static void main(String[] args) throws Exception { ToolRunner.run(new DemoWordCount(), args); } }