Note the name is important. It must be exactly equal to the class name. Before running the code set the environment variables as follows
export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64/
export PATH=${JAVA_HOME}/bin:${PATH}
export HADOOP_CLASSPATH=${JAVA_HOME}/lib/tools.jar
Compile WordCount.java and create a jar:
$ hadoop com.sun.tools.javac.Main WordCount.java jar cf wc.jar WordCount*.class
Create two files for input to the Map-Reduce. We will make two files in the input folder as follows
mkdir input echo "Hello World Bye World" > input/file01 echo "Hello Hadoop Goodbye Hadoop" > input/file02
We also need to create the input folder on HDFS
hadoop fs -mkdir -p /user/$USER/input
Now we need to move these files into HDFS
hadoop fs -copyFromLocal input/ /user/$USER/
Verify that the files have been copied
hadoop fs -ls /user/zaid/input
It should show two files as follows
Found 2 items -rw-r--r-- 1 zaid supergroup 22 2020-04-17 09:55 /user/zaid/input/file01 -rw-r--r-- 1 zaid supergroup 28 2020-04-17 09:55 /user/zaid/input/file02
Now lets run the application
hadoop jar wc.jar WordCount /user/$USER/input /user/$USER/output
The program should run and show a lot of output and hopefully no errors. Once complete you can check the output as follows
$ hadoop fs -cat /user/$USER/output/part-r-00000
