Java – type mismatched keys from the map: expected Text,received … LongWritable

I have a simple Hadoop application that takes a CSV file, splits the entries with "," and then calculates the first item

Here is my code

package com.bluedolphin;

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.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reporter;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

public class MyJob extends Configured implements Tool {
    private final static LongWritable one = new LongWritable(1);


    public static class MapClass extends Mapper<Object,Text,LongWritable> {
        private Text word = new Text();
        public void map(Object key,Text value,OutputCollector<Text,LongWritable> output,Reporter reporter) throws IOException,InterruptedException {
            String[] citation = value.toString().split(",");
            word.set(citation[0]);
            output.collect(word,one);
        }
    }

    public static class Reduce extends Reducer<Text,LongWritable,LongWritable> {
        public void reduce(
                Text key,Iterator<LongWritable> values,InterruptedException {
            int sum = 0;

            while (values.hasNext()) {
                sum += values.next().get();
            }
            output.collect(key,new LongWritable(sum));
        }
    }
    public static class Combiner extends Reducer<Text,IntWritable,new LongWritable(sum));

        }
    }

    public int run(String[] args) throws Exception {
        Configuration conf = getConf();

        Job job = new Job(conf,"MyJob");
        job.setJarByClass(MyJob.class);

        Path in = new Path(args[0]);
        Path out = new Path(args[1]);

        FileInputFormat.setInputPaths(job,in);
        FileOutputFormat.setOutputPath(job,out);

        job.setMapperClass(MapClass.class);
    //  job.setCombinerClass(Combiner.class);
        job.setReducerClass(Reduce.class);
    //  job.setInputFormatClass(KeyValueInputFormat.class);
        job.setInputFormatClass(TextInputFormat.class);
    //  job.setOutputFormatClass(KeyValueOutputFormat.class);

        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(LongWritable.class);

        System.exit(job.waitForCompletion(true) ? 0 : 1);
        return 0;
    }

    public static void main(String args[]) throws Exception {
        int res = ToolRunner.run(new Configuration(),new MyJob(),args);
        System.exit(res);
    }
}

This is an error:

11/12/16 22:16:58 INFO mapred.JobClient: Task Id : attempt_201112161948_0005_m_000000_0,Status : Failed
java.io.IOException: Type mismatch in key from map: expected org.apache.hadoop.io.Text,recieved org.apache.hadoop.io.LongWritable
    at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.collect(MapTask.java:1013)
    at org.apache.hadoop.mapred.MapTask$NewOutputCollector.write(MapTask.java:690)
    at org.apache.hadoop.mapreduce.TaskInputOutputContext.write(TaskInputOutputContext.java:80)
    at org.apache.hadoop.mapreduce.Mapper.map(Mapper.java:124)
    at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:144)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:763)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:369)
    at org.apache.hadoop.mapred.Child$4.run(Child.java:259)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:416)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1059)
    at org.apache.hadoop.mapred.Child.main(Child.java:253)

Solution

Several things to fix in the code

>The old (o.a.h.mapred) and the new API (o.a.h.mapreduce) are incompatible, so they should not be mixed

import org.apache.hadoop.mapred.OutputCollector;  
import org.apache.hadoop.mapred.Reporter;  
import org.apache.hadoop.mapreduce.Job;  
import org.apache.hadoop.mapreduce.Mapper;  
import org.apache.hadoop.mapreduce.Reducer;

>Ensure that the input / output type of the mapper / reducer is o.a.h.io Writable. Mapper's input key is object, making it longwritable. > It seems that the functions of combiner and reducer are the same, so you don't need to repeat it

job.setCombinerClass(Reducer.class);

In addition, you can use the wordcount sample, and your requirements are not much different from the wordcount sample