hadoop jar
The hadoop jar
command runs a program contained in
a JAR file. Users can bundle their MapReduce code in a JAR file and
execute it using this command.
Syntax
hadoop jar <jar>
[<arguments>]
Parameters
The following commands parameters are supported for hadoop
jar
:
Parameter |
Description |
---|---|
|
The JAR file. |
|
Arguments to the program specified in the JAR file. |
Examples
Streaming ApplicationHadoop streaming applications
are run using the hadoop jar
command. The Hadoop streaming utility
enables you to create and run MapReduce applications with any executable or script as
the mapper and/or the
reducer.
$ hadoop jar $HADOOP_HOME/hadoop-streaming.jar \
-input myInputDirs \
-output myOutputDir \
-mapper org.apache.hadoop.mapred.lib.IdentityMapper \
-reducer /bin/wc
The
-input
, -output
, -mapper
, and
-reducer
streaming command options are all required for streaming
jobs. Either an executable or a Java class may be used for the mapper and the reducer.
For more information about and examples of streaming applications, see
Hadoop Streaming
at the Apache project's page.
The simple Word
Count program is another example of a program that is run using the hadoop
jar
command. The wordcount
functionality is built into the
hadoop-0.20.2-dev-examples.jar
program. You pass the file, along
with the location, to Hadoop with the hadoop jar
command and Hadoop
reads the JAR file and executes the relevant instructions.
The Word Count program reads files from an input directory, counts the words, and writes the results of the application to files in an output directory.
$ hadoop jar /opt/mapr/hadoop/hadoop-0.20.2/hadoop-0.20.2-dev-examples.jar wordcount /myvolume/in /myvolume/out