java - 如何使用 WritableComparator Hadoop

Question

下面是我使用 WritableComparator 的代码片段，但它不起作用

import org.apache.hadoop.io.WritableComparable;import org.apache.hadoop.io.WritableComparator;public class MovieComparator extends WritableComparator{    public MovieComparator(){        super(Movie.class);    }    @Override    public int compare(WritableComparable o,WritableComparable o2){        System.out.println("in compare");        Movie m = (Movie)o;        Movie m2 = (Movie)o2;        System.out.println(m.compareTo(m2));        return m.movieId.compareTo(m2.movieId);    }}

public class Movie implements WritableComparable {    Text movieId;    Text movieTitle;    public Movie(Text movieId, Text movieTitle) {        this.movieId = movieId;        this.movieTitle = movieTitle;    }    public Movie(){    }    public String getMovieId() {        return movieId.toString();    }    public void setMovieId(String movieId) {        this.movieId = new Text(movieId);    }    public String getMovieTitle() {        return movieTitle.toString();    }    public void setMovieTitle(String movieTitle) {        this.movieTitle = new Text(movieTitle);    }    @Override    public void readFields(DataInput in) throws IOException {        //movieId = in.read;        movieId.readFields(in);        movieTitle.readFields(in);    }    @Override    public void write(DataOutput out) throws IOException {        //out.writeUTF(movieId);        //out.writeUTF(movieTitle);        movieId.write(out);        movieTitle.write(out);    }    @Override    public int compareTo(Movie o) {    //  System.out.println("in compareTo");        int res=movieTitle.compareTo(o.movieTitle);        return res;    }    @Override    public int hashCode(){        return movieId.hashCode();    }    @Override    public boolean equals(Object o){        Movie m=(Movie)o;         return movieId.equals(m.movieId);    }    @Override    public String toString(){        return movieTitle.toString();    }}In driver class I am setting the comparator by below line
job.setSortComparatorClass(MovieComparator.class);
任何人都可以告诉我我在这方面错在哪里吗？它在下面给出了异常(exception) 
14/09/08 14:17:03 WARN mapred.LocalJobRunner: job_local_0001java.io.IOException: Spill failed    at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.collect(MapTask.java:1029)    at org.apache.hadoop.mapred.MapTask$NewOutputCollector.write(MapTask.java:691)    at org.apache.hadoop.mapreduce.TaskInputOutputContext.write(TaskInputOutputContext.java:80)    at com.impetus.MovieMapper.map(MovieMapper.java:44)    at com.impetus.MovieMapper.map(MovieMapper.java:1)    at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:144)    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:764)    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)    at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:212)

Answer 1

我发现了一个问题，我将不得不使用 super(Movie.class,true)，而不是使用 super(Movie.class)。通过发送 true，WritableComparator 将实例化对象，否则它将在比较方法中传递 null