source: sample/WordCountFromHBase.java @ 9

/**
 * Program: WordCountFromHBase.java
 * Editor: Waue Chen 
 * From :  NCHC. Taiwn
 * Last Update Date: 06/13/2008
 */

/**
 * Purpose : 
 *  Word counting from Hbase then store result in Hadoop file system 
 * 
 * HowToUse : 
 *  Make sure Hadoop file system are running and HBase has correct data.
 *  Suggest to run WordCountIntoHBase first.
 *  finally, modify these setup parameters and run.
 * 
 * Check Result:
 *  
 *  inspect http://localhost:50070 by web explorer
 */

package tw.org.nchc.code;

import java.io.IOException;
import java.util.Iterator;
import java.util.StringTokenizer;
import java.io.FileOutputStream;
import java.io.File;
import java.io.RandomAccessFile;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hbase.HStoreKey;
import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
import org.apache.hadoop.hbase.mapred.TableInputFormat;
import org.apache.hadoop.hbase.mapred.TableMap;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.MapWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.JobClient;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.MapReduceBase;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reducer;
import org.apache.hadoop.mapred.Reporter;
@SuppressWarnings("unused")

public class WordCountFromHBase {
  /* setup parameters */
  // set the output path 
  static String outputPath = "counts2";

  // org.apache.hadoop.hbase.mapred.TableMap<K,V>  \ 
  // TableMap<K extends org.apache.hadoop.io.WritableComparable, \ 
  //  V extends org.apache.hadoop.io.Writable> \
  // Scan an HBase table to sort by a specified sort column. \
  // If the column does not exist, the record is not passed to Reduce.;
  private static class MapClass extends TableMap<Text, IntWritable> {

    // set one as (IntWritable)1
    private final static IntWritable one = new IntWritable(1);
    // set column 
    private final static Text textcol = new Text(WordCountIntoHBase.colstr);
    private Text word = new Text();   
    // TableMap is a interface, map is a abstract method. now, we should \
    //  inprement map() at here, format is : \
    // map(HStoreKey key, MapWritable value,  \
    //  OutputCollector<K,V> output, Reporter reporter) ;
        // Call a user defined function on a single HBase record, \  
    //  represented by a key and its associated record value. ; 
    public void map(HStoreKey key, MapWritable cols,
        OutputCollector<Text, IntWritable> output, Reporter reporter)
        throws IOException {
      // 
      // The first get() is : Writable <- get(Object key) \
      //  get in interface Map<Writable,Writable>  ;
      // Use ImmutableBytesWritable to downcast Writable \
      // The second get() is : byte[] <- get() \
      //  Get the data from the BytesWritable. ;
      // Text.decode is parse UTF-8 code to a String ;
      // per "line" is per row data in HTable 
      String line = Text.decode( ((ImmutableBytesWritable) cols.get(textcol) )
          .get() );
      
      //let us know what is "line"
      /*
      RandomAccessFile raf = 
        new RandomAccessFile("/home/waue/mr-result.txt","rw");
      raf.seek(raf.length()); // move pointer to end
      raf.write(("\n"+line).getBytes());
      raf.close();
      *///end
      // the result is the contents of merged files "
      
      //StringTokenizer will divide a line into a word  
      StringTokenizer itr = new StringTokenizer(line);
      // set every word as one
      while (itr.hasMoreTokens()) {
        // nextToken will return this value in String and point to next \
        // Text.set() = Set to contain the contents of a string.
        word.set(itr.nextToken());  
        // OutputCollector.collect = collect(K key, V value) \
        //  Adds a key/value pair to the output.
        output.collect(word, one);
      }
    }
  }

  // reducer: sums up all the counts
  private static class ReduceClass extends MapReduceBase implements
      Reducer<Text, IntWritable, Text, IntWritable> {

    // reuse objects
    private final static IntWritable SumValue = new IntWritable();
    
    // this sample's reduce() format is the same as map() \
    //  reduce is a method waiting for implement \
    //  four type in this sample is (Text , Iterator<IntWritable>, \
    //    OutputCollector<Text, IntWritable> , Reporter ) ;
    public void reduce(Text key, Iterator<IntWritable> values,
        OutputCollector<Text, IntWritable> output, Reporter reporter)
        throws IOException {
      // sum up value
      int sum = 0;
      // "key" is word , "value" is sum 
      // why values.hasNext(), not key.hasNext()
      while (values.hasNext()) { 
        // next() will return this value and pointer to next event \
        //  IntWritable.get() will transfer IntWritable to Int
        sum += values.next().get(); 
      }
      // IntWritable.set(int) will transfer Int to IntWritable
      SumValue.set(sum);
      // hense we set outputPath in main, the output.collect will put 
      //  data in Hadoop
      output.collect(key, SumValue);
    }
  }

  private WordCountFromHBase() {
  }

  /**
   * Runs the demo.
   */
  public static void main(String[] args) throws IOException {
    

    int mapTasks = 1;
    int reduceTasks = 1;
    // initialize job;
    JobConf conf = new JobConf(WordCountFromHBase.class);
    // TableMap.initJob will build HBase code \
    //  "org.apache.hadoop.hbase.mapred.TableMap".initJob \
    //  (Table_name,column_string,Which_class_will_use,job_configure);
    TableMap.initJob(WordCountIntoHBase.Table_Name,
        WordCountIntoHBase.colstr, MapClass.class, conf);
    conf.setJobName(WordCountIntoHBase.Table_Name + "store");
    conf.setNumMapTasks(mapTasks);
    conf.setNumReduceTasks(reduceTasks);
    
    //Set the key class for the job output data.
    conf.setOutputKeyClass(Text.class);
    //Set the value class for job outputs.
    conf.setOutputValueClass(IntWritable.class);
    // MapperClass,CombinerClass,ReducerClass are essential
    conf.setMapperClass(MapClass.class);
    conf.setCombinerClass(ReduceClass.class);
    conf.setReducerClass(ReduceClass.class);
    // input is Hbase format => TableInputFormat
    conf.setInputFormat(TableInputFormat.class);
    conf.setOutputPath(new Path(outputPath));
//     delete the old path with the same name 
    FileSystem.get(conf).delete(new Path(outputPath));
    JobClient.runJob(conf);
  }
}