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This article is about how Hadoop implements HelloWorld. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

Purpose: to export the Hello,World in the input file to the file as World Hello.

Enter the contents of the file:

Code example:

Import java.io.IOException;import java.text.SimpleDateFormat;import java.util.Date;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.LongWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Job;import org.apache.hadoop.mapreduce.Mapper;import org.apache.hadoop.mapreduce.Reducer;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;import org.apache.hadoop.mapreduce.lib.input.TextInputFormat Import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat / * HelloWorld Job * will input the Hello,World in the file Output as World Hello to file * / public class HelloWorld {/ * mapper * to preprocess our data * / private static class MyMapper extends Mapper {@ Override protected void map (LongWritable key, Text value, Context context) throws IOException InterruptedException {System.out.println ("mapper running...") System.out.println ("key=" + key.get ()); System.out.println ("value=" + value.toString ()); String [] strValue = value.toString (). Split (","); context.write (new Text (strValue [1]), new Text (strValue [0])) }} / * processor * is used for business calculation of data records preprocessed by mapper. Then output * / private static class MyReducer extends Reducer {@ Override protected void reduce (Text key, Iterable values, Context context) throws IOException, InterruptedException {System.out.println ("reducer running...") System.out.println ("key=" + key.toString ()); String val = values.iterator (). Next (). ToString (); System.out.println ("value=" + val); context.write (key, new Text (val)) } public static void main (String [] args) throws IOException, ClassNotFoundException, InterruptedException {Configuration configuration = new Configuration (); Job job = new Job (configuration, "helloworld_job"); job.setJarByClass (HelloWorld.class); job.setMapperClass (MyMapper.class); job.setReducerClass (MyReducer.class) Job.setInputFormatClass (TextInputFormat.class); job.setOutputKeyClass (Text.class); job.setOutputValueClass (Text.class); FileInputFormat.addInputPath (job, new Path ("hdfs://hadoopmaster:9000/in/helloworld.txt")) String outFileExt = "_" + new SimpleDateFormat ("yyyyMMddHHmmss") .format (new Date ()); FileOutputFormat.setOutputPath (job, new Path ("hdfs://hadoopmaster:9000/out/helloworld" + outFileExt)); System.out.println (job.waitForCompletion (true));}}

Package the code and copy it to hadoopmaster:

Execute the jar package:

Hadoop jar helloworld.jar

Get the output file:

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