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Hadoop Beginner's Guide

Time for action – running WordCount on a local Hadoop cluster

Now we have generated the class files and collected them into a JAR file, we can run the application by performing the following steps:

  1. Submit the new JAR file to Hadoop for execution. 
    $ hadoop jar wc1.jar WordCount1 test.txt output
  2. If successful, you should see the output being very similar to the one we obtained when we ran the Hadoop-provided sample WordCount in the previous chapter. Check the output file; it should be as follows: 
    $ Hadoop fs –cat output/part-r-00000
This 1
yes 1
a 1
is 2
test 1
this 1

What just happened?

This is the first time we have used the Hadoop JAR command with our own code. There are four arguments:

  1. The name of the JAR file.
  2. The name of the driver class within the JAR file.
  3. The location, on HDFS, of the input file (a relative reference to the /user/Hadoop home folder, in this case).
  4. The desired location of the output folder (again, a relative path).

Tip

The name of the driver class is only required if a main class has not (as in this case) been specified within the JAR file manifest.

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