Running WordCount v1.0

You can run WordCount v1.0 in your own Hadoop environment. If you do not have one available, you can download and install the Cloudera QuickStart VM.

  1. Before you run the sample, you must create input and output locations in HDFS. Use the following commands to create the input directory/user/cloudera/wordcount/input in HDFS:
    $ sudo su hdfs
    $ hadoop fs -mkdir /user/cloudera
    $ hadoop fs -chown cloudera /user/cloudera
    $ exit
    $ sudo su cloudera
    $ hadoop fs -mkdir /user/cloudera/wordcount /user/cloudera/wordcount/input 
  2. Create sample text files to use as input, and move them to the/user/cloudera/wordcount/input directory in HDFS. You can use any files you choose; for convenience, the following shell commands create a few small input files for illustrative purposes. The Makefile also contains most of the commands that follow.
    $ echo "Hadoop is an elephant" > file0
    $ echo "Hadoop is as yellow as can be" > file1
    $ echo "Oh what a yellow fellow is Hadoop" > file2
    $ hadoop fs -put file* /user/cloudera/wordcount/input 
  3. Compile the WordCount class.

    To compile in a package installation of CDH:

    $ mkdir -p build
    $ javac -cp /usr/lib/hadoop/*:/usr/lib/hadoop-mapreduce/* -d build -Xlint 

    To compile in a parcel installation of CDH:

    $ mkdir -p build
    $ javac -cp /opt/cloudera/parcels/CDH/lib/hadoop/*:/opt/cloudera/parcels/CDH/lib/hadoop-mapreduce/* \ -d build -Xlint 
  4. Create a JAR file for the WordCount application.
    $ jar -cvf wordcount.jar -C build/ . 
  5. Run the WordCount application from the JAR file, passing the paths to the input and output directories in HDFS.
    $ hadoop jar wordcount.jar org.myorg.WordCount /user/cloudera/wordcount/input /user/cloudera/wordcount/output 

    When you look at the output, all of the words are listed in UTF-8 alphabetical order (capitalized words first). The number of occurrences from all input files has been reduced to a single sum for each word.

    $ hadoop fs -cat /user/cloudera/wordcount/output/*
    Hadoop    3
    Oh        1
    a         1
    an        1
    as        2
    be        1
    can       1
    elephant  1
    fellow    1
    is        3
    what      1
    yellow    2
  6. If you want to run the sample again, you first need to remove the output directory. Use the following command.
    $ hadoop fs -rm -r /user/cloudera/wordcount/output