title: Hadoop : NoSuchMethodException
body: <p>This is the job, which joins two relations,</p>
  
  <pre><code>import org.apache.hadoop.mapred.*;
  import org.apache.hadoop.conf.*;
  import org.apache.hadoop.util.*;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.io.*;
  import org.apache.hadoop.contrib.utils.join.*;
  import java.io.*;
  
  public class TwoByTwo extends Configured implements Tool
  {
      public static class MapClass extends DataJoinMapperBase
      {
          protected Text generateInputTag( String inputFile)
          {
              String datasource = inputFile.split( "\\.")[ 0];
              return new Text( datasource);
          }//end generateInputTag
  
          protected Text generateGroupKey( TaggedMapOutput aRecord)
          {
              String line =  ( ( Text) aRecord.getData()).toString();
              //between two relations there may be more than one common attributes
              //so group key has to include all these common attributes. Common
              //attributes begin with an '_'( underscore).
              String[] tokens = line.split(",");
              String groupKey = "";
              for( String s : tokens)
              {
                  if( s.charAt( 0) == '_')
                  {
                      groupKey = groupKey + s;
                  }
              }
              return new Text( groupKey);
          }//end generateGroupKey
  
          protected TaggedMapOutput generateTaggedMapOutput( Object value)
          {
              TaggedWritable retv = new TaggedWritable( ( Text) value);
              retv.setTag( this.inputTag);
              return retv;
          }//end TaggedMapOutput
      }//end MapClass
  
      public static class Reduce extends DataJoinReducerBase
      {
          protected TaggedMapOutput combine( Object[] tags, Object[] values)
          {
              if( tags.length &lt; 2)
              {
                  return null;
              }
              String joinedStr = "";
              for( int i = 0; i &lt; values.length; i++)
              {
                  if( i &gt; 0)
                  {
                      joinedStr += ",";
                  }
                  TaggedWritable tw = ( TaggedWritable) values[ i];
                  String line = ( ( Text) tw.getData()).toString();
                  String[] tokens = line.split( ",", 2);
                  joinedStr += tokens[ 1];
              }
              TaggedWritable retv = new TaggedWritable( new Text( joinedStr));
              retv.setTag( ( Text) tags[ 0]);
              return retv;
          }//end TaggedMapOutput
      }//end Reduce
  
      public static class TaggedWritable extends TaggedMapOutput
      {
          private Writable data;
  
          public TaggedWritable( Writable data)
          {
              this.tag = new Text( "");
              this.data = data;
          }//end TaggedWritable
  
          public Writable getData()
          {
              return data;
          }//end getData
  
          public void write( DataOutput out) throws IOException
          {
              this.tag.write( out);
              this.data.write( out);
          }//end write
  
          public void readFields( DataInput in) throws IOException
          {
              this.tag.readFields( in);
              this.data.readFields( in);      
          }//end readFields
      }//end TaggedWritable
  
      public int run( String[] args) throws Exception
      {
          Configuration conf = getConf();
  
          JobConf job = new JobConf( conf, TwoByTwo.class);
  
          Path in  = new Path( "relations/");
          Path out = new Path( "relout/");
          FileInputFormat.setInputPaths( job, in);
          FileOutputFormat.setOutputPath( job, out);
  
          job.setJobName( "TwoByTwo");
          job.setMapperClass( MapClass.class);
          job.setReducerClass( Reduce.class);
  
          job.setInputFormat( TextInputFormat.class);
          job.setOutputFormat( TextOutputFormat.class);
          job.setOutputKeyClass( Text.class);
          job.setOutputValueClass( TaggedWritable.class);
          job.set("mapred.textoutputformat.separator", ",");
  
          JobClient.runJob( job);
          return 0;
      }//end run
  
      public static void main( String[] args) throws Exception
      {
          int res = ToolRunner.run( new Configuration(), new TwoByTwo(), args);
  
          System.exit( res);
      }//end main
  }
  </code></pre>
  
  <p>When I run this job,</p>
  
  <pre><code>bin/hadoop jar /home/hduser/TwoByTwo.jar TwoByTwo -libjars /usr/local/hadoop/contrib/datajoin/hadoop-datajoin-1.0.3.jar
  </code></pre>
  
  <p>MapClass runs appropriately. When Reduce runs after sometime of running I get this NoSuchMethodException</p>
  
  <pre><code>12/10/18 16:38:17 INFO mapred.JobClient:  map 100% reduce 27%
  12/10/18 16:38:19 INFO mapred.JobClient: Task Id : attempt_201210181416_0013_r_000000_0, Status : FAILED
  java.lang.RuntimeException: java.lang.NoSuchMethodException: TwoByTwo$TaggedWritable.&lt;init&gt;()
      at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:115)
      at org.apache.hadoop.io.serializer.WritableSerialization$WritableDeserializer.deserialize(WritableSerialization.java:62)
      at org.apache.hadoop.io.serializer.WritableSerialization$WritableDeserializer.deserialize(WritableSerialization.java:40)
      at org.apache.hadoop.mapred.Task$ValuesIterator.readNextValue(Task.java:1271)
      at org.apache.hadoop.mapred.Task$ValuesIterator.next(Task.java:1211)
      at org.apache.hadoop.mapred.ReduceTask$ReduceValuesIterator.moveToNext(ReduceTask.java:249)
      at org.apache.hadoop.mapred.ReduceTask$ReduceValuesIterator.next(ReduceTask.java:245)
      at org.apache.hadoop.contrib.utils.join.DataJoinReducerBase.regroup(DataJoinReducerBase.java:106)
      at org.apache.hadoop.contrib.utils.join.DataJoinReducerBase.reduce(DataJoinReducerBase.java:129)
      at org.apache.hadoop.mapred.ReduceTask.runOldReducer(ReduceTask.java:519)
      at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:420)
      at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
      at java.security.AccessController.doPrivileged(Native Method)
      at javax.security.auth.Subject.doAs(Subject.java:415)
      at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121)
      at org.apache.hadoop.mapred.Child.main(Child.java:249)
  Caused by: java.lang.NoSuchMethodException: TwoByTwo$TaggedWritable.&lt;init&gt;()
      at java.lang.Class.getConstructor0(Class.java:2721)
      at java.lang.Class.getDeclaredConstructor(Class.java:2002)
      at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:109)
      ... 15 more
  </code></pre>
  
  <p>I have problem with nested class TaggedWritable. Why do I have problem with this class on reduce side and not on map side? How can I resolve this error? The constraint of two relations plays any role to the error? Thanks for any help.</p>