MultipleInputs in Map Reduce
MultipleInputs in Map Reduce (Union Operator)
Problem : The job is expected to read two Files having different schema . (Github)
<dependencies>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-client</artifactId>
<version>2.6.0-cdh5.9.0<version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-hdfs</artifactId>
<version>2.6.0-cdh5.9.0<version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-common</artifactId>
<version>2.6.0-cdh5.9.0<version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-mapreduce-client-core</artifactId>
<version>2.6.0-cdh5.9.0</version>
</dependency>
</dependencies>
<repositories>
<repository>
<id>cloudera</id>
<url>https://repository.cloudera.com/artifactory/cloudera-repos/</url>
</repository>
</repositories>
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Left Mapper :
package com.big.data.mapreduce.multiinputpath;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import java.io.IOException;
public class StudentToIdMapper extends Mapper<LongWritable, Text, Text, IntWritable> {
// As TextInput Format has been used ,
// the key is the offset of line in the file , The actual line goes in the value
private Text outputName;
private IntWritable outputId;
@Override
protected void setup(Context context) throws IOException, InterruptedException {
super.setup(context);
outputName = new Text();
outputId = new IntWritable();
}
// Input StudentName,RollId
@Override
public void map(LongWritable key, Text value,
Context context) throws IOException, InterruptedException {
String[] studentId = value.toString().split(MultiInputPathDriver.DELIMTER);
outputName.set(studentId[0]);
outputId.set(Integer.parseInt(studentId[1]));
context.write(outputName, outputId);
}
}
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Right Mapper :
package com.big.data.mapreduce.multiinputpath;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import java.io.IOException;
public class IdtoStudentMapper extends Mapper<LongWritable, Text, Text, IntWritable> {
// As TextInput Format has been used ,
// the key is the offset of line in the file , The actual line goes in the value
private Text outputName;
private IntWritable outputId;
@Override
protected void setup(Context context) throws IOException, InterruptedException {
super.setup(context);
outputName = new Text();
outputId = new IntWritable();
}
// Input RollId,StudentName
@Override
public void map(LongWritable key, Text value,
Context context) throws IOException, InterruptedException {
String[] studentId = value.toString().split(MultiInputPathDriver.DELIMTER);
outputName.set(studentId[1]);
outputId.set(Integer.parseInt(studentId[0]));
context.write(outputName, outputId);
}
}
Driver:
package com.big.data.mapreduce.multiinputpath;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.MultipleInputs;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;
import java.io.IOException;
public class MultiInputPathDriver extends Configured implements Tool {
//extends Configured implements Tool helps in argument parsing .
// Arguments need to passed as -Dkey=Value
public static final String INPUT_PATH_LEFT = "input.path.left";
public static final String INPUT_PATH_RIGHT = "input.path.right";
public static final String OUTPUT_PATH = "output.path";
public static final String DELIMTER = ",";
public static void main(String[] args) throws Exception {
if (ToolRunner.run(new MultiInputPathDriver(), args) != 0) {
throw new IOException("Job has failed");
}
}
@Override
public int run(String[] args) throws Exception {
//The arguments passed has been split into Key value by ToolRunner
Configuration conf = getConf();
Path inputPathLeft = new Path(conf.get(INPUT_PATH_LEFT));
Path inputPathRight = new Path(conf.get(INPUT_PATH_RIGHT));
Path outputPath = new Path(conf.get(OUTPUT_PATH));
Job job = new Job(conf, this.getClass().toString());
// For left path set StudentToIdMapper ,
// For right path set IdtoStudentMapper ,
// as the schema are different hence different mapper
MultipleInputs.addInputPath(job, inputPathLeft,
TextInputFormat.class, StudentToIdMapper.class);
MultipleInputs.addInputPath(job, inputPathRight,
TextInputFormat.class, IdtoStudentMapper.class);
//This is the base Path for the sub directories , the extra path will be added in the mapper .
FileOutputFormat.setOutputPath(job, outputPath);
job.setJobName("MultiOutputPathDriver");
job.setJarByClass(MultiInputPathDriver.class);
//Set OutPutFormat class
job.setOutputFormatClass(TextOutputFormat.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(IntWritable.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
//As no reducers are used, its a map only task
job.setNumReduceTasks(0);
// Driver polls to find out if the job has completed or not.
return job.waitForCompletion(true) ? 0 : 1;
}
}
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Working code can be found at Github
package com.big.data.mapreduce.multiinputpath;
import com.cloudera.org.joda.time.DateTime;
import org.apache.commons.io.FileUtils;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.junit.AfterClass;
import org.junit.Assert;
import org.junit.BeforeClass;
import org.junit.Test;
import java.io.File;
import java.io.IOException;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
public class MultiInputPathTest {
private final Configuration conf = new Configuration();
private static FileSystem fs;
private static final DateTime NOW = DateTime.now();
private static String baseDir;
private static String outputDir;
private static String leftdir;
private static String rightdir;
private static final String NEW_LINE_DELIMETER = "\n";
private static Map<String, Integer> studentToId;
@BeforeClass
public static void startup() throws Exception {
Configuration conf = new Configuration();
//set the fs to file:/// which means the local fileSystem
conf.set("fs.default.name", "file:///");
conf.set("mapred.job.tracker", "local");
fs = FileSystem.getLocal(conf);
baseDir = "/tmp/mapreduce/multiinputPath/" + UUID.randomUUID().toString() + "/";
leftdir = baseDir + "left";
rightdir = baseDir + "right";
outputDir = baseDir + "/output/";
//Write the data into the local filesystem for Left input
File tempFileleft = new File(leftdir + "/input.txt");
FileUtils.writeStringToFile(tempFileleft, "Maverick,1", "UTF-8");
FileUtils.writeStringToFile(tempFileleft, NEW_LINE_DELIMETER, "UTF-8", true);
FileUtils.writeStringToFile(tempFileleft, "Ninja,2", "UTF-8", true);
//Write the data into the local filesystem for Left input
File tempFileRight = new File(rightdir + "/input.txt");
FileUtils.writeStringToFile(tempFileRight, "3,Zoom", "UTF-8");
FileUtils.writeStringToFile(tempFileRight, NEW_LINE_DELIMETER, "UTF-8", true);
FileUtils.writeStringToFile(tempFileRight, "4,Dracula", "UTF-8", true);
studentToId = new HashMap<>();
}
@AfterClass
public static void cleanup() throws Exception {
//Delete the local filesystem folder after the Job is done
fs.delete(new Path(baseDir), true);
}
void fileToHashMap(String filePath) throws IOException {
//Read the data from the outputfile
File outputFile = new File(filePath);
String fileToString = FileUtils.readFileToString(outputFile, "UTF-8");
//4 lines in output file, with one word per line
Arrays.stream(fileToString.split(NEW_LINE_DELIMETER)).forEach(e -> {
String[] wordCount = e.split("\t");
studentToId.put(wordCount[0], Integer.parseInt(wordCount[1]));
});
}
@Test
public void multiInputTest() throws Exception {
// Any argument passed with -DKey=Value will be parsed by ToolRunner
String[] args = new String[]{
"-D" + MultiInputPathDriver.INPUT_PATH_LEFT + "=" + leftdir,
"-D" + MultiInputPathDriver.INPUT_PATH_RIGHT + "=" + rightdir,
"-D" + MultiInputPathDriver.OUTPUT_PATH + "=" + outputDir};
// call the main function to run the job
MultiInputPathDriver.main(args);
//Two mappers have been spawned because,
//Two input files are there and InputFormat is
//TextInputFormat (with CombinedTextInputFormat this will not be the case)
fileToHashMap(outputDir + "/part-m-00000");
fileToHashMap(outputDir + "/part-m-00001");
//4 words .
Assert.assertEquals(4L, studentToId.size());
Assert.assertEquals(1L, studentToId.get("Maverick").longValue());
}
}