java - org.apache.hadoop.io.Text无法转换为org.apache.hadoop.io.NullWritable

Question

我想将序列文件转换为MapReduce中的ORC文件。
键/值的输入类型为文本/文本。

我的程序看起来像

public class ANR extends Configured implements Tool{


public static void main(String[] args) throws  Exception {
    // TODO Auto-generated method stub

     int res = ToolRunner.run(new Configuration(),new ANR(), args);
     System.exit(res); 
}

public int run(String[] args) throws Exception {
    Logger log = Logger.getLogger(ANRmap.class.getName());
    Configuration conf = getConf();
    Job job;

    String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();

     conf.set("orc.create.index", "true");  


     job = Job.getInstance(conf);

 /////

    job.setJobName("ORC Output"); 
    job.setJarByClass(ANR.class);
    job.setInputFormatClass(SequenceFileInputFormat.class);
    SequenceFileInputFormat.addInputPath(job, new Path(args[0]));   
    job.setMapperClass(ANRmap.class);
    job.setNumReduceTasks(0);
    job.setOutputFormatClass(OrcNewOutputFormat.class);  
    OrcNewOutputFormat.setCompressOutput(job,true);  

      OrcNewOutputFormat.setOutputPath(job,new Path(args[1]));  

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

映射器

    public class ANRmap extends Mapper<Text,Text,NullWritable,Writable> {
    private final OrcSerde serde = new OrcSerde(); 

     public void map(Text key, Text value,
                OutputCollector<NullWritable, Writable> output)
                throws IOException {
            output.collect(NullWritable.get(),serde.serialize(value, null));
        }
}

这是异常(exception)

Error: java.lang.ClassCastException: org.apache.hadoop.io.Text cannot be cast to org.apache.hadoop.io.NullWritable
    at org.apache.hadoop.hive.ql.io.orc.OrcNewOutputFormat$OrcRecordWriter.write(OrcNewOutputFormat.java:37)
    at org.apache.hadoop.mapred.MapTask$NewDirectOutputCollector.write(MapTask.java:635)
    at org.apache.hadoop.mapreduce.task.TaskInputOutputContextImpl.write(TaskInputOutputContextImpl.java:89)
    at org.apache.hadoop.mapreduce.lib.map.WrappedMapper$Context.write(WrappedMapper.java:112)
    at org.apache.hadoop.mapreduce.Mapper.map(Mapper.java:124)
    at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:145)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:764)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:340)
    at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:168)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:415)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1594)
    at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:163)

OrcNewOutputFormat中的输出键为NullWritable。如何将Text转换为NullWritable或以其他方式解决此异常？

Answer 1

尝试使用 Context 而不是 OutputCollector 。

public class ReduceTask extends Reducer<Text,Text, Text, NullWritable>{

    public void reduce(Text key,Iterable<Text> values,Context context){

        for(Text value:values){
            try {
                context.write(key,NullWritable.get());
            } catch (IOException e) {

                e.printStackTrace();
            } catch (InterruptedException e) {

                e.printStackTrace();
            }
        }

    }
}