Grep.java example

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/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.hadoop.examples;

import java.util.Random;

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.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.SequenceFileInputFormat;
import org.apache.hadoop.mapreduce.lib.map.InverseMapper;
import org.apache.hadoop.mapreduce.lib.map.RegexMapper;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.SequenceFileOutputFormat;
import org.apache.hadoop.mapreduce.lib.reduce.LongSumReducer;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

/* Extracts matching regexs from input files and counts them. */
public class Grep extends Configured implements Tool {
  private Grep() {}                               // singleton

  public int run(String[] args) throws Exception {
    if (args.length < 3) {
      System.out.println("Grep <inDir> <outDir> <regex> [<group>]");
      ToolRunner.printGenericCommandUsage(System.out);
      return 2;
    }

    Path tempDir =
      new Path("grep-temp-"+
          Integer.toString(new Random().nextInt(Integer.MAX_VALUE)));

    Configuration conf = getConf();
    conf.set(RegexMapper.PATTERN, args[2]);
    if (args.length == 4)
      conf.set(RegexMapper.GROUP, args[3]);

    Job grepJob = new Job(conf);
    
    try {
      
      grepJob.setJobName("grep-search");

      FileInputFormat.setInputPaths(grepJob, args[0]);

      grepJob.setMapperClass(RegexMapper.class);

      grepJob.setCombinerClass(LongSumReducer.class);
      grepJob.setReducerClass(LongSumReducer.class);

      FileOutputFormat.setOutputPath(grepJob, tempDir);
      grepJob.setOutputFormatClass(SequenceFileOutputFormat.class);
      grepJob.setOutputKeyClass(Text.class);
      grepJob.setOutputValueClass(LongWritable.class);

      grepJob.waitForCompletion(true);

      Job sortJob = new Job(conf);
      sortJob.setJobName("grep-sort");

      FileInputFormat.setInputPaths(sortJob, tempDir);
      sortJob.setInputFormatClass(SequenceFileInputFormat.class);

      sortJob.setMapperClass(InverseMapper.class);

      sortJob.setNumReduceTasks(1);                 // write a single file
      FileOutputFormat.setOutputPath(sortJob, new Path(args[1]));
      sortJob.setSortComparatorClass(          // sort by decreasing freq
        LongWritable.DecreasingComparator.class);

      sortJob.waitForCompletion(true);
    }
    finally {
      FileSystem.get(conf).delete(tempDir, true);
    }
    return 0;
  }

  public static void main(String[] args) throws Exception {
    int res = ToolRunner.run(new Configuration(), new Grep(), args);
    System.exit(res);
  }

}