Its may be SequenceFileInputFormat reading the value as <Text,LongWritable>
by default. So u can write like
SequenceFileInputFormat<Text,ByteWritable> sequenceInputFormat = new
SequenceFileInputFormat<Text,ByteWritable>();
job.setInputFormat(sequenceInputFormat.getClass());
On Fri, Jan 21, 2011 at 2:25 AM, Luca <luca_...@yahoo.com> wrote:
> Hello,
>
> I recently started to use Hadoop and I have a problem while using a Mapfile
> as a input to a MapReduce job.
>
> The following working code, write a simple MapFile called "TestMap" in hdfs
> where there are three keys of type Text and three value of type
> BytesWritable
>
> $ hadoop fs -text /user/hadoop/TestMap/data
> 11/01/20 11:17:58 INFO util.NativeCodeLoader: Loaded the native-hadoop
> library
> 11/01/20 11:17:58 INFO zlib.ZlibFactory: Successfully loaded & initialized
> native-zlib library
> 11/01/20 11:17:58 INFO compress.CodecPool: Got brand-new decompressor
> A 01
> B 02
> C 03
>
>
>
> import java.io.IOException;
> import org.apache.hadoop.conf.Configuration;
> import org.apache.hadoop.fs.FileSystem;
> import org.apache.hadoop.io.MapFile;
> import org.apache.hadoop.io.Text;
> import org.apache.hadoop.io.BytesWritable;
> import org.apache.hadoop.io.SequenceFile;
> import org.apache.hadoop.io.IOUtils;
>
> public class CreateMap {
>
> public static void main(String[] args) throws IOException{
>
> Configuration conf = new Configuration();
> FileSystem hdfs = FileSystem.get(conf);
>
> Text key = new Text();
> BytesWritable value = new BytesWritable();
> byte[] data = {1, 2, 3};
> String[] strs = {"A", "B", "C"};
> int bytesRead;
> MapFile.Writer writer = null;
>
> writer = new MapFile.Writer(conf, hdfs, "TestMap", key.getClass(),
> value.getClass());
> try {
> for (int i = 0; i < 3; i++) {
> key.set(strs[i]);
> value.set(data, i, 1);
> writer.append(key, value);
> System.out.println(strs[i] + ":" + data[i] + " added.");
> }
> }
> catch (IOException e) {
> e.printStackTrace();
> }
> finally {
> IOUtils.closeStream(writer);
> }
> }
> }
>
> The simple MapReduce job that follows try to increment by one the values of
> the mapfile:
>
> import java.io.IOException;
> import java.util.Iterator;
> import org.apache.hadoop.conf.Configuration;
> import org.apache.hadoop.conf.Configured;
> import org.apache.hadoop.fs.Path;
> import org.apache.hadoop.io.Text;
> import org.apache.hadoop.mapred.FileInputFormat;
> import org.apache.hadoop.mapred.FileOutputFormat;
> import org.apache.hadoop.mapred.JobClient;
> import org.apache.hadoop.mapred.JobConf;
> import org.apache.hadoop.mapred.SequenceFileInputFormat;
> import org.apache.hadoop.mapred.MapReduceBase;
> import org.apache.hadoop.mapred.Mapper;
> import org.apache.hadoop.mapred.OutputCollector;
> import org.apache.hadoop.mapred.Reducer;
> import org.apache.hadoop.mapred.Reporter;
> import org.apache.hadoop.mapred.TextOutputFormat;
> import org.apache.hadoop.util.Tool;
> import org.apache.hadoop.util.ToolRunner;
> import org.apache.hadoop.io.BytesWritable;
>
>
> public class AddOne extends Configured implements Tool {
>
> public static class MapClass extends MapReduceBase
>
> implements Mapper<Text, BytesWritable, Text, Text> {
>
> public void map(Text key, BytesWritable value,
> OutputCollector<Text, Text> output,
> Reporter reporter) throws IOException {
>
>
> byte[] data = value.getBytes();
> data[0] += 1;
> value.set(data, 0, 1);
> output.collect(key, new Text(value.toString()));
> }
> }
>
> public static class Reduce extends MapReduceBase
> implements Reducer<Text, Text, Text, Text> {
>
> public void reduce(Text key, Iterator<Text> values,
> OutputCollector<Text, Text> output,
> Reporter reporter) throws IOException {
>
> output.collect(key, values.next());
> }
> }
>
> public int run(String[] args) throws Exception {
> Configuration conf = getConf();
>
> JobConf job = new JobConf(conf, AddOne.class);
>
> Path in = new Path("TestMap");
> Path out = new Path("output");
> FileInputFormat.setInputPaths(job, in);
> FileOutputFormat.setOutputPath(job, out);
>
> job.setJobName("AddOne");
> job.setMapperClass(MapClass.class);
> job.setReducerClass(Reduce.class);
>
> job.setInputFormat(SequenceFileInputFormat.class);
> job.setMapOutputKeyClass(Text.class);
> job.setMapOutputValueClass(Text.class);
>
> job.setOutputFormat(TextOutputFormat.class);
> job.setOutputKeyClass(Text.class);
> job.setOutputValueClass(Text.class);
> job.set("key.value.separator.in.input.line", ":");
>
>
> JobClient.runJob(job);
>
> return 0;
> }
>
> public static void main(String[] args) throws Exception {
> int res = ToolRunner.run(new Configuration(), new AddOne(), args);
>
> System.exit(res);
> }
> }
>
> The runtime exception that I get is:
> java.lang.ClassCastException: org.apache.hadoop.io.LongWritable cannot be
> cast to org.apache.hadoop.io.BytesWritable
> at AddOne$MapClass.map(AddOne.java:32)
> at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:50)
> at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:358)
> at org.apache.hadoop.mapred.MapTask.run(MapTask.java:307)
> at org.apache.hadoop.mapred.Child.main(Child.java:170)
>
>
> I don't understand why hadoop is trying to cast a LongWritable, since in my
> code I define the Mapper interface correctly(Mapper<Text, BytesWritable,
> Text, Text>).
>
> Could somebody help me?
>
> Thank you very much
>
>
> Luca
>
>
>
>
>
>
>
