How to Execute Character Count Program in MapReduce Hadoop?
Prerequisites: Hadoop and MapReduce
Required setup for completing the below task.
Our task is to count the frequency of each character present in our input file. We are using Java for implementing this particular scenario. However, The MapReduce program can also be written in Python or C++. Execute the below steps to complete the task for finding the occurrence of each character.
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Step 1: First Open Eclipse -> then select File -> New -> Java Project ->Name it CharCount -> then select use an execution environment -> choose JavaSE-1.8 then next -> Finish.
Step 2: Create Three Java Classes into the project. Name them CharCountDriver(having the main function), CharCountMapper, CharCountReducer.
Mapper Code: You have to copy and paste this program into the CharCountMapper Java Class file.
Reducer Code: You have to copy-paste this below program into the CharCountReducer Java Class file.
Driver Code: You have to copy-paste this below program into the CharCountDriver Java Class file.
Step 3: Now we need to add an external jar for the packages that we have import. Download the jar package Hadoop Common and Hadoop MapReduce Core according to your Hadoop version. You can check Hadoop Version with the below command:
Step 4: Now we add these external jars to our CharCount project. Right Click on CharCount -> then select Build Path-> Click on Configure Build Path and select Add External jars…. and add jars from it’s download location then click -> Apply and Close.
Step 5: Now export the project as a jar file. Right-click on CharCount choose Export.. and go to Java -> JAR file click -> Next and choose your export destination then click -> Next. Choose Main Class as CharCount by clicking -> Browse and then click -> Finish -> Ok.
Now the Jar file is successfully created and saved at /Documents directory with the name charectercount.jar in my case.
Step 6: Create a simple text file and add some data to it.
You can also add text to the file manually or using some other editor like Vim or gedit.
To see the content of the file use cat command available in Linux.
Step 7: Start our Hadoop Daemons
Step 8: Move your test.txt file to the Hadoop HDFS.
hdfs dfs -put /file_path /destination
In below command / shows the root directory of our HDFS.
hdfs dfs -put /home/dikshant/Documents/test.txt /
Check the file is present in the root directory of HDFS or not.
hdfs dfs -ls /
Step 9: Now Run your Jar File with the below command and produce the output in CharCountResult File.
hadoop jar /jar_file_location /dataset_location_in_HDFS /output-file_name
hadoop jar /home/dikshant/Documents/charectercount.jar /test.txt /CharCountResult
Step 10: Now Move to localhost:50070/, under utilities select Browse the file system and download part-r-00000 in /CharCountResult directory to see result. we can also check the result i.e. that part-r-00000 file with cat command as shown below.
hdfs dfs -cat /CharCountResult/part-00000
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