Java tutorial
/* * Cloud9: A Hadoop toolkit for working with big data * * 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. */ import java.io.IOException; import java.util.Arrays; import java.util.Iterator; 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.FloatWritable; import org.apache.hadoop.io.IntWritable; 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.input.SequenceFileInputFormat; import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat; import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat; import org.apache.hadoop.util.Tool; import org.apache.hadoop.util.ToolRunner; import org.apache.log4j.Logger; import edu.umd.cloud9.util.TopNScoredObjects; import edu.umd.cloud9.util.pair.PairOfObjectFloat; public class FindMaxPageRankNodes extends Configured implements Tool { private static final Logger LOG = Logger.getLogger(FindMaxPageRankNodes.class); private static class MyMapper extends Mapper<IntWritable, PageRankNode, IntWritable, FloatWritable> { private TopNScoredObjects<Integer> queue; @Override public void setup(Context context) throws IOException { int k = context.getConfiguration().getInt("n", 100); queue = new TopNScoredObjects<Integer>(k); } @Override public void map(IntWritable nid, PageRankNode node, Context context) throws IOException, InterruptedException { queue.add(node.getNodeId(), node.getPageRank()); } @Override public void cleanup(Context context) throws IOException, InterruptedException { IntWritable key = new IntWritable(); FloatWritable value = new FloatWritable(); for (PairOfObjectFloat<Integer> pair : queue.extractAll()) { key.set(pair.getLeftElement()); value.set(pair.getRightElement()); context.write(key, value); } } } private static class MyReducer extends Reducer<IntWritable, FloatWritable, IntWritable, FloatWritable> { private static TopNScoredObjects<Integer> queue; @Override public void setup(Context context) throws IOException { int k = context.getConfiguration().getInt("n", 100); queue = new TopNScoredObjects<Integer>(k); } @Override public void reduce(IntWritable nid, Iterable<FloatWritable> iterable, Context context) throws IOException { Iterator<FloatWritable> iter = iterable.iterator(); queue.add(nid.get(), iter.next().get()); // Shouldn't happen. Throw an exception. if (iter.hasNext()) { throw new RuntimeException(); } } @Override public void cleanup(Context context) throws IOException, InterruptedException { IntWritable key = new IntWritable(); FloatWritable value = new FloatWritable(); for (PairOfObjectFloat<Integer> pair : queue.extractAll()) { key.set(pair.getLeftElement()); value.set(pair.getRightElement()); context.write(key, value); } } } public FindMaxPageRankNodes() { } private static final String INPUT = "input"; private static final String OUTPUT = "output"; private static final String TOP = "top"; /** * 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("top n").create(TOP)); 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) || !cmdline.hasOption(TOP)) { 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 n = Integer.parseInt(cmdline.getOptionValue(TOP)); LOG.info("Tool name: " + FindMaxPageRankNodes.class.getSimpleName()); LOG.info(" - input: " + inputPath); LOG.info(" - output: " + outputPath); LOG.info(" - top: " + n); Configuration conf = getConf(); conf.setInt("mapred.min.split.size", 1024 * 1024 * 1024); conf.setInt("n", n); Job job = Job.getInstance(conf); job.setJobName(FindMaxPageRankNodes.class.getName() + ":" + inputPath); job.setJarByClass(FindMaxPageRankNodes.class); job.setNumReduceTasks(1); FileInputFormat.addInputPath(job, new Path(inputPath)); FileOutputFormat.setOutputPath(job, new Path(outputPath)); job.setInputFormatClass(SequenceFileInputFormat.class); job.setOutputFormatClass(TextOutputFormat.class); job.setMapOutputKeyClass(IntWritable.class); job.setMapOutputValueClass(FloatWritable.class); job.setOutputKeyClass(IntWritable.class); job.setOutputValueClass(FloatWritable.class); job.setMapperClass(MyMapper.class); job.setReducerClass(MyReducer.class); // Delete the output directory if it exists already. FileSystem.get(conf).delete(new Path(outputPath), true); job.waitForCompletion(true); return 0; } /** * Dispatches command-line arguments to the tool via the {@code ToolRunner}. */ public static void main(String[] args) throws Exception { int res = ToolRunner.run(new FindMaxPageRankNodes(), args); System.exit(res); } }