Error: java.io.IOException: wrong value class: class org.apache.hadoop.io.Text is not class Myclass

Question

I have my mapper and reducers as follows. But I am getting some kind of strange exception. I can't figure out why is it throwing such kind of exception.

public static class MyMapper implements Mapper<LongWritable, Text, Text, Info> {

    @Override
    public void map(LongWritable key, Text value,
        OutputCollector<Text, Info> output, Reporter reporter)
        throws IOException {
        Text text = new Text("someText")
            //process 
        output.collect(text, infoObjeject);
    }

}

public static class MyReducer implements Reducer<Text, Info, Text, Text> {

    @Override
    public void reduce(Text key, Iterator<Info> values,
        OutputCollector<Text, Text> output, Reporter reporter)
        throws IOException {
        String value = "xyz" //derived in some way
        //process
        output.collect(key, new Text(value)); //exception occurs at this line
    }

}

System.out.println("Starting v14 ");
JobConf conf = new JobConf(RouteBuilderJob.class);
conf.setJobName("xyz");

String jarLocation =ClassUtil.findContainingJar(getClass());

System.out.println("path of jar file = " + jarLocation);

conf.setJarByClass(RouteBuilderJob.class);

conf.setMapOutputKeyClass(Text.class);
conf.setMapOutputValueClass(Info.class);

conf.setOutputKeyClass(Text.class);
conf.setOutputValueClass(Text.class);

//am i missing something here???

conf.setMapperClass(RouteBuilderJob.RouteMapper.class);
conf.setCombinerClass(RouteBuilderJob.RouteReducer.class);
conf.setReducerClass(RouteBuilderJob.RouteReducer.class);


conf.setInputFormat(TextInputFormat.class);
conf.setOutputFormat(TextOutputFormat.class);

FileInputFormat.setInputPaths(conf, new Path(args[0]));
FileOutputFormat.setOutputPath(conf, new Path(args[1]));

JobClient.runJob(conf);

I am getting an exception:

Error: java.io.IOException: wrong value class: class org.apache.hadoop.io.Text is not class com.xyz.mypackage.Info
at org.apache.hadoop.mapred.IFile$Writer.append(IFile.java:199)
at org.apache.hadoop.mapred.Task$CombineOutputCollector.collect(Task.java:1307)
at com.xyz.mypackage.job.MyJob$RouteReducer.reduce(MyJob.java:156)
at com.xyz.mypackage.job.MyJob$RouteReducer.reduce(MyJob.java:1)

Internally info object (which implements Writable) is serialized using Text

@Override
public void write(DataOutput out) throws IOException {
    Gson gson = new Gson();
    String searlizedStr = gson.toJson(this);
    Text.writeString(out, searlizedStr);
}

@Override
public void readFields(DataInput in) throws IOException {
    String s = Text.readString(in);
    Gson gson = new Gson();
    JsonReader jsonReader = new JsonReader(new StringReader(s));
    jsonReader.setLenient(true);

Info info = gson.fromJson(jsonReader, Info.class);
    //set fields using this.somefield = info.getsomefield() 
}

what is "value" here . I dont find any declaration or anything for "value" variable ? "output.collect(key, new Text(value));" in this line — backtrack
– backtrack, Commented Jan 27, 2014 at 9:35
@Backtrack can you help me with this?i have spent lot of time debuging this — user93796
– user93796, Commented Jan 27, 2014 at 9:40
Problem solved after the combiner was removed. @Backtrack thanks backtrack — user93796
– user93796, Commented Jan 27, 2014 at 10:43

b4hand · Accepted Answer · 2014-05-04 16:55:17Z

7

Technically the output types of your reduce should be the same as your input type. This must be true if you use a combiner as the output of the combiner is fed into your reducer.

answered May 4, 2014 at 16:55

b4hand

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1 Comment

Abhi Over a year ago

Helped me too. But any specific reason why would reducer want both types to remain same

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