我不知道如何使用multipleoutputs类。我用它来创建多个输出文件。下面是我的驱动程序类的代码片段

Configuration conf = new Configuration();

    Job job = Job.getInstance(conf);
    job.setJarByClass(CustomKeyValueTest.class);//class with mapper and reducer
    job.setOutputKeyClass(CustomKey.class);
    job.setOutputValueClass(Text.class);
    job.setMapOutputKeyClass(CustomKey.class);
    job.setMapOutputValueClass(CustomValue.class);
    job.setMapperClass(CustomKeyValueTestMapper.class);
    job.setReducerClass(CustomKeyValueTestReducer.class);
    job.setInputFormatClass(TextInputFormat.class);

    Path in = new Path(args[1]);
    Path out = new Path(args[2]);
    out.getFileSystem(conf).delete(out, true);

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

    MultipleOutputs.addNamedOutput(job, "islnd" , TextOutputFormat.class, CustomKey.class, Text.class);
    LazyOutputFormat.setOutputFormatClass(job, TextOutputFormat.class);
    MultipleOutputs.setCountersEnabled(job, true);

    boolean status = job.waitForCompletion(true);

在减速机中，我使用了这样的倍数输出，

private MultipleOutputs<CustomKey, Text> multipleOutputs;

@Override
public void setup(Context context) throws IOException, InterruptedException {
    multipleOutputs = new MultipleOutputs<>(context);
}

@Override
public void reduce(CustomKey key, Iterable<CustomValue> values, Context context) throws IOException, InterruptedException {
    ...
     multipleOutputs.write("islnd", key, pop, key.toString());
    //context.write(key, pop);

}

public void cleanup() throws IOException, InterruptedException {
    multipleOutputs.close();
}

}
当我使用context.write时，我会得到包含数据的输出文件。但是当我删除context.write时，输出文件是空的。但我不想调用context.write，因为它会创建额外的文件part-r-00000。如这里所述（类描述的最后一段），我使用lazyoutputformat来避免part-r-00000文件。但还是没用。