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POClassCast Error while writing to Cassandra from hadoop job
 

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    <p>I am running a hadoop job and trying to write the output to Cassandra. I am getting following exception:</p> <pre><code>java.lang.ClassCastException: org.apache.hadoop.io.Text cannot be cast to java.nio.ByteBuffer at org.apache.cassandra.hadoop.ColumnFamilyRecordWriter.write(ColumnFamilyRecordWriter.java:60) at org.apache.hadoop.mapred.ReduceTask$NewTrackingRecordWriter.write(ReduceTask.java:514) at org.apache.hadoop.mapreduce.TaskInputOutputContext.write(TaskInputOutputContext.java:80) at org.apache.hadoop.mapreduce.Reducer.reduce(Reducer.java:156) at org.apache.hadoop.mapreduce.Reducer.run(Reducer.java:176) at org.apache.hadoop.mapred.ReduceTask.runNewReducer(ReduceTask.java:572) at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:414) at org.apache.hadoop.mapred.Child$4.run(Child.java:270) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:396) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1127) at org.apache.hadoop.mapred.Child.main(Child.java:264) </code></pre> <p>I modeled my map reduce code on the WordCount example given at <a href="https://wso2.org/repos/wso2/trunk/carbon/dependencies/cassandra/contrib/word_count/src/WordCount.java" rel="nofollow">https://wso2.org/repos/wso2/trunk/carbon/dependencies/cassandra/contrib/word_count/src/WordCount.java</a></p> <p>Here's my MR code:</p> <pre><code>public class SentimentAnalysis extends Configured implements Tool { static final String KEYSPACE = "Travel"; static final String OUTPUT_COLUMN_FAMILY = "Keyword_PtitleId"; public static class Map extends Mapper&lt;LongWritable, Text, Text, LongWritable&gt; { private Text word = new Text(); public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException { String line = value.toString(); Sentiment sentiment = null; try { sentiment = (Sentiment) PojoMapper.fromJson(line, Sentiment.class); } catch(Exception e) { return; } if(sentiment != null &amp;&amp; sentiment.isLike()) { word.set(sentiment.getNormKeyword()); context.write(word, new LongWritable(sentiment.getPtitleId())); } } } public static class Reduce extends Reducer&lt;Text, LongWritable, ByteBuffer, List&lt;Mutation&gt;&gt; { private ByteBuffer outputKey; public void reduce(Text key, Iterator&lt;LongWritable&gt; values, Context context) throws IOException, InterruptedException { List&lt;Long&gt; ptitles = new ArrayList&lt;Long&gt;(); java.util.Map&lt;Long, Integer&gt; ptitleToFrequency = new HashMap&lt;Long, Integer&gt;(); while (values.hasNext()) { Long value = values.next().get(); ptitles.add(value); } for(Long ptitle : ptitles) { if(ptitleToFrequency.containsKey(ptitle)) { ptitleToFrequency.put(ptitle, ptitleToFrequency.get(ptitle) + 1); } else { ptitleToFrequency.put(ptitle, 1); } } byte[] keyBytes = key.getBytes(); outputKey = ByteBuffer.wrap(Arrays.copyOf(keyBytes, keyBytes.length)); for(Long ptitle : ptitleToFrequency.keySet()) { context.write(outputKey, Collections.singletonList(getMutation(new Text(ptitle.toString()), ptitleToFrequency.get(ptitle)))); } } private static Mutation getMutation(Text word, int sum) { Column c = new Column(); byte[] wordBytes = word.getBytes(); c.name = ByteBuffer.wrap(Arrays.copyOf(wordBytes, wordBytes.length)); c.value = ByteBuffer.wrap(String.valueOf(sum).getBytes()); c.timestamp = System.currentTimeMillis() * 1000; Mutation m = new Mutation(); m.column_or_supercolumn = new ColumnOrSuperColumn(); m.column_or_supercolumn.column = c; return m; } } public static void main(String[] args) throws Exception { int ret = ToolRunner.run(new SentimentAnalysis(), args); System.exit(ret); } @Override public int run(String[] args) throws Exception { Configuration conf = new Configuration(); Job job = new Job(conf, "SentimentAnalysis"); job.setJarByClass(SentimentAnalysis.class); String inputFile = args[0]; job.setMapperClass(Map.class); job.setReducerClass(Reduce.class); job.setMapOutputKeyClass(Text.class); job.setMapOutputValueClass(LongWritable.class); job.setOutputKeyClass(ByteBuffer.class); job.setOutputValueClass(List.class); job.setOutputFormatClass(ColumnFamilyOutputFormat.class); job.setInputFormatClass(TextInputFormat.class); ConfigHelper.setOutputColumnFamily(job.getConfiguration(), KEYSPACE, OUTPUT_COLUMN_FAMILY); FileInputFormat.setInputPaths(job, inputFile); ConfigHelper.setRpcPort(job.getConfiguration(), "9160"); ConfigHelper.setInitialAddress(job.getConfiguration(), "localhost"); ConfigHelper.setPartitioner(job.getConfiguration(), "org.apache.cassandra.dht.RandomPartitioner"); boolean success = job.waitForCompletion(true); return success ? 0 : 1; } </code></pre> <p>}</p> <p>If you look under the Reduce class, I am converting Text field (key) to ByteBuffer properly. </p> <p>Would appreciate some pointers on how to fix this.</p>
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