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Hadoop Useful Utility Classes

Some handy classes for using Hadoop / Map Reduce / Hbase

IDENTITYMAPPER  / IDENTITYREDUCER

org.apache.hadoop.mapreduce.Mapper<KEYIN,VALUEIN,KEYOUT,VALUEOUT>
org.apache.hadoop.mapreduce.Reducer<KEYIN,VALUEIN,KEYOUT,VALUEOUT>

jar : hadoop-core.jar

if your mappers and reducers write inputs to outputs, then use these guys.  No need to receate them.


SHELL  / SHELLCOMMANDEXECUTOR

org.apache.hadoop.util.Shell
org.apache.hadoop.util.Shell.ShellCommandExecutor

jar : hadoop-core.jar

handy for executing commands on local machine and inspect outputs

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import org.apache.hadoop.util.Shell.ShellCommandExecutor;



 



String[] cmd =    { "ls", "/usr" };



ShellCommandExecutor shell = new ShellCommandExecutor(cmd);



shell.execute();



System.out.println("* shell exit code : " + shell.getExitCode());



System.out.println("* shell output: \n" + shell.getOutput());



 



/* output:



* shell exit code : 0



* shell output: 



X11



X11R6



bin



etc



include



lib



libexec



llvm-gcc-4.2



local



sbin



share



standalone



*/

STRINGUTILS

org.apache.hadoop.util.StringUtils

jar : hadoop-core.jar

lots of functions to deal with Strings.  I will highlight a few

StringUtils.byteDesc() : User-friendly / human-readable byte lengths

how many megabytes is 10000000 bytes?   this will tell you.

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import org.apache.hadoop.util.StringUtils;



 



// --- human readable  byte lengths -----



System.out.println ("1024 bytes = " + StringUtils.byteDesc(1024));



System.out.println ("67108864 bytes = " + StringUtils.byteDesc(67108864));



System.out.println ("1000000 bytes = " + StringUtils.byteDesc(1000000));



 



/* produces:



1024 bytes = 1 KB



67108864 bytes = 64 MB



1000000 bytes = 976.56 KB



*/

StringUtils.byteToHexString() : Convert Bytes to Hex strings and vice-versa

We deal with byte arrays in Hadoop / map reduce.  This is a handy way to print / debug issues

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import org.apache.hadoop.util.StringUtils;



 



// ----------------- String Utils : bytes <--> hex ---------



String s = "aj89y1_xxy";



byte[] b = s.getBytes();



String hex = StringUtils.byteToHexString(b);



byte[] b2 = StringUtils.hexStringToByte(hex);



String s2 = new String(b2);



System.out.println(s + " --> " + hex + " <-- " + s2);



 



/* output:



aj89y1_xxy --> 616a383979315f787879 <-- aj89y1_xxy



*/
StringUtils.formatTime() :  human readable elapsed time

how long is 100000000 ms?   see below

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System.out.println ("1000000 ms = " + StringUtils.formatTime(1000000));



long t1 = System.currentTimeMillis();



// execute a command



long t2 = System.currentTimeMillis();



t2 += 10000000; // adjust for this demo



System.out.println ("operation took : " + StringUtils.formatTimeDiff(t2, t1));



 



/* output:



1000000 ms = 16mins, 40sec



operation took : 2hrs, 46mins, 40sec



*/


HADOOP CLUSTER STATUS

ClusterStatus : org.apache.hadoop.mapred.ClusterStatus

jar : hadoop-core.jar

Find out how many nodes are in the cluster, how many mappers, reducers ...etc

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package sujee;



 



import org.apache.hadoop.conf.Configuration;



import org.apache.hadoop.conf.Configured;



import org.apache.hadoop.mapred.ClusterStatus;



import org.apache.hadoop.mapred.JobClient;



import org.apache.hadoop.mapred.JobConf;



import org.apache.hadoop.util.Tool;



import org.apache.hadoop.util.ToolRunner;



 



/*



compile into a jar and execute:



     hadoop jar a.jar sujee.TestCluster



 



output:



number of task trackers: 1



maximum map tasks : 3



currently running map tasks : 0



 



*/



 



public class TestCluster extends Configured implements Tool



{



    public static void main(String[] args) throws Exception



    {



        int result = ToolRunner.run(new Configuration(), new TestCluster(), args);



        System.exit(result);



    }



 



    @Override



    public int run(String[] arg0) throws Exception



    {



        JobConf dummyJob = new JobConf(new Configuration(), TestCluster.class);



        JobClient jobClient = new JobClient(dummyJob);



        ClusterStatus clusterStatus = jobClient.getClusterStatus();



        System.out.println("number of task trackers: " + clusterStatus.getTaskTrackers());



        System.out.println("maximum map tasks : " + clusterStatus.getMaxMapTasks());



        System.out.println("currently running map tasks : " + clusterStatus.getMapTasks());



        return 0;



    }



}

Hbase Handy Classes


BYTES
org.apache.hadoop.hbase.util.Bytes

jar : hbase*.jar

handy utility for dealing with bytes and byte arrays

Bytes.toBytes() : convert objects to bytes

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 // -------- Bytes.toBytes() : converting objects to bytes ------



int i = 10000;



byte [] intBytes = Bytes.toBytes(i);



System.out.println ("int " + i + " in bytes : " + Arrays.toString(intBytes));



            



float f = (float) 999.993;



byte [] floatBytes = Bytes.toBytes(f);



System.out.println ("float " + f + " in bytes : " + Arrays.toString(floatBytes));



            



String s = "foobar";



byte [] stringBytes = Bytes.toBytes(s);



System.out.println ("string " + s + " in bytes : " + Arrays.toString(stringBytes));



 



/* output:



int 10000 in bytes : [0, 0, 39, 16]



float 999.993 in bytes : [68, 121, -1, -115]



string foobar in bytes : [102, 111, 111, 98, 97, 114]



*/

Bytes.add()  : create composite keys

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// ---------- Bytes.add() : creating composite keys ---------



// rowkey = int + long



int i = 0;



long timestamp = System.currentTimeMillis();



byte [] rowkey2 = Bytes.add(Bytes.toBytes(i), Bytes.toBytes(timestamp));



System.out.println ("rowkey2 (" + rowkey2.length + ") : " + Arrays.toString(rowkey2));



 



// add also supports adding 3 byte arrays



// rowkey = int + str + long



byte[] rowkey3 = Bytes.add(Bytes.toBytes(0) , Bytes.toBytes("hello"),  Bytes.toBytes(timestamp)); 



System.out.println ("rowkey3 (" + rowkey3.length + ") : " + Arrays.toString(rowkey3));



 



/* output:



rowkey2 (12) : [0, 0, 0, 0, 0, 0, 1, 50, 8, -101, 99, -41]



rowkey3 (17) : [0, 0, 0, 0, 104, 101, 108, 108, 111, 0, 0, 1, 50, 8, -101, 99, -41]



*/

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