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.demo; import java.io.IOException; import java.util.Iterator; import java.util.StringTokenizer; 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.WritableComparable; 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.Reducer; import org.apache.hadoop.mapred.Reporter; import org.apache.hadoop.mapred.SequenceFileInputFormat; import org.apache.hadoop.mapred.SequenceFileOutputFormat; import org.apache.hadoop.util.Tool; import org.apache.hadoop.util.ToolRunner; import org.apache.log4j.Logger; import org.json.JSONException; import edu.umd.cloud9.io.JSONObjectWritable; /** * <p> * Demo that illustrates use of {@link JSONObjectWritable} objects as * intermediate keys in a MapReduce job. This Hadoop Tool takes the following * command-line arguments: * </p> * * <ul> * <li>[input-path] input path</li> * <li>[output-path] output path</li> * <li>[num-mappers] number of mappers</li> * <li>[num-reducers] number of reducers</li> * </ul> * * <p> * Input comes from a flat text collection packed into a SequenceFile with * {@link DemoPackJSON}. Output shows the count of words on even- and * odd-length lines. * </p> * * <p> * Format of the output SequenceFile: The key is a JSON object. The field named * "Token" contains a word and the field named "EvenOrOdd" indicates whether the * word was found on a even-length or odd-length line. The value is the count of * the word on either even- or odd-length lines. * </p> * * @see DemoWordCountTuple1 * @see DemoWordCountTuple2 * * @author Jimmy Lin */ public class DemoWordCountJSON extends Configured implements Tool { private static final Logger sLogger = Logger.getLogger(DemoWordCountJSON.class); // define custom intermediate key; must specify sort order public static class MyKey extends JSONObjectWritable implements WritableComparable { public int compareTo(Object obj) { try { MyKey that = (MyKey) obj; String thisToken = this.getStringUnchecked("Token"); String thatToken = that.getStringUnchecked("Token"); // if tokens are equal, must check "EvenOrOdd" field if (thisToken.equals(thatToken)) { // otherwise, sort by "EvenOrOdd" field int thisEO = this.getIntUnchecked("EvenOrOdd"); int thatEO = that.getIntUnchecked("EvenOrOdd"); if (thisEO < thatEO) return -1; if (thisEO > thatEO) return 1; // if we get here, it means the tuples are equal return 0; } // determine sort order based on token return thisToken.compareTo(thatToken); } catch (JSONException e) { e.printStackTrace(); throw new RuntimeException("Unexpected error comparing JSON objects!"); } } public int hashCode() { int val = -1; try { val = this.getStringUnchecked("Token").hashCode(); } catch (JSONException e) { throw new RuntimeException("Unexpected error with JSON objects!"); } return val; } } // mapper that emits a json object as the key, and value '1' for each // occurrence protected static class MyMapper extends MapReduceBase implements Mapper<LongWritable, JSONObjectWritable, MyKey, IntWritable> { // define value '1' statically so we can reuse the object, i.e., avoid // unnecessary object creation private final static IntWritable one = new IntWritable(1); // once again, reuse keys if possible private final static MyKey key = new MyKey(); public void map(LongWritable dummy, JSONObjectWritable jsonIn, OutputCollector<MyKey, IntWritable> output, Reporter reporter) throws IOException { try { // the input value is a JSON object String line = (String) jsonIn.get("text"); StringTokenizer itr = new StringTokenizer(line); while (itr.hasMoreTokens()) { String token = itr.nextToken(); // put new values into the tuple key.clear(); key.put("Token", token); key.put("EvenOrOdd", line.length() % 2); // emit key-value pair output.collect(key, one); } } catch (JSONException e) { e.printStackTrace(); throw new RuntimeException("Unexpected error with JSON objects!"); } } } // reducer counts up tuple occurrences protected static class MyReducer extends MapReduceBase implements Reducer<MyKey, IntWritable, MyKey, IntWritable> { private final static IntWritable SumValue = new IntWritable(); public void reduce(MyKey keyIn, Iterator<IntWritable> values, OutputCollector<MyKey, IntWritable> output, Reporter reporter) throws IOException { // sum values int sum = 0; while (values.hasNext()) { sum += values.next().get(); } // keep original tuple key, emit sum of counts as value SumValue.set(sum); output.collect(keyIn, SumValue); } } /** * Creates an instance of this tool. */ public DemoWordCountJSON() { } private static int printUsage() { System.out.println("usage: [input-path] [output-path] [num-mappers] [num-reducers]"); ToolRunner.printGenericCommandUsage(System.out); return -1; } /** * Runs this tool. */ public int run(String[] args) throws Exception { if (args.length != 4) { printUsage(); return -1; } String inputPath = args[0]; String outputPath = args[1]; int numMapTasks = Integer.parseInt(args[2]); int numReduceTasks = Integer.parseInt(args[3]); sLogger.info("Tool: DemoWordCountJSON"); sLogger.info(" - input path: " + inputPath); sLogger.info(" - output path: " + outputPath); sLogger.info(" - number of mappers: " + numMapTasks); sLogger.info(" - number of reducers: " + numReduceTasks); JobConf conf = new JobConf(DemoWordCountTuple1.class); conf.setJobName("DemoWordCountJSON"); conf.setNumMapTasks(numMapTasks); conf.setNumReduceTasks(numReduceTasks); FileInputFormat.setInputPaths(conf, new Path(inputPath)); FileOutputFormat.setOutputPath(conf, new Path(outputPath)); FileOutputFormat.setCompressOutput(conf, false); conf.setInputFormat(SequenceFileInputFormat.class); conf.setOutputKeyClass(MyKey.class); conf.setOutputValueClass(IntWritable.class); conf.setOutputFormat(SequenceFileOutputFormat.class); conf.setMapperClass(MyMapper.class); conf.setCombinerClass(MyReducer.class); conf.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(); JobClient.runJob(conf); sLogger.info("Job Finished in " + (System.currentTimeMillis() - startTime) / 1000.0 + " seconds"); 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 DemoWordCountJSON(), args); System.exit(res); } }