我创建了一个hadoop自定义可写程序，如下所示

public class ResultType implements Writable {

    private Text xxxx;
    private Text yyyy;
    private Text zzzz;

    public ResultType() {}

    public ResultType(Text xxxx, Text yyyy, Text zzzz) {
        this.xxxx = xxxx;
        this.yyyy = yyyy;
        this.zzzz = zzzz;   
    }

    public Text getxxxx() {
        return this.xxxx;
    }

    public Text getyyyy() {
        return this.yyyy;
    }

    public Text getzzzz() {
        return this.zzzz;
    }

    @Override
    public void readFields(DataInput in) throws IOException {
        xxxx.readFields(in);
        yyyy.readFields(in);
        zzzz.readFields(in);
    }

    @Override
    public void write(DataOutput out) throws IOException {
        xxxx.write(out);
        yyyy.write(out);
        zzzz.write(out);
    }
}

我的Map程序代码是

public static class Mapper1 extends TableMapper<Text, ResultType> {

    private Text text = new Text();

    @Override
    public void map(ImmutableBytesWritable row, Result values, Context context)
            throws IOException, InterruptedException {

        // getting name value

        String xxxx = new String(values.getValue(Bytes.toBytes("cf"), Bytes.toBytes("xxxx")));
        String yyyy = new String(values.getValue(Bytes.toBytes("cf"), Bytes.toBytes("yyyy")));
        String zzzz = new String(values.getValue(Bytes.toBytes("cf"), Bytes.toBytes("zzzz")));
        text.set(xxxx);
        context.write(text, new ResultType(new Text(xxxx), new Text(yyyy), new Text(zzzz)));

    }
}

我的代码是

public static class Reducer1 extends Reducer<Text, ResultType, Text, ResultType> {

    public void reduce(Text key, Iterable<ResultType> values, Context context)
            throws IOException, InterruptedException {

        List<ResultType> returnset = new ArrayList<ResultType>();
        Map<String, ResultType> duplicatelist = new HashMap<String, ResultType>();
        boolean iskeyadded = true;

        for (ResultType val : values) {

            Text yyyy = val.getyyyy();
            Text zzzz = val.getzzzz();

            String groupkey = yyyy + "," + zzzz ;

            if (duplicatelist.containsKey(groupkey)) {

                if (iskeyadded) {
                    context.write(key, new ResultType(new Text(key), new Text(yyyy),
                            new Text(zzzz)));
                    iskeyadded = false;
                }

                context.write(key, new ResultType(new Text(key), new Text(yyyy), new Text(zzzz)));

            } else {
                duplicatelist.put(groupkey, val);
            }
        }

    }
}

当我运行这个代码时

Ignoring exception during close for org.apache.hadoop.mapred.MapTask$NewOutputCollector@20890b6f
java.lang.NullPointerException
    at test.ResultType.readFields(ResultType.java)
    at org.apache.hadoop.io.serializer.WritableSerialization$WritableDeserializer.deserialize(WritableSerialization.java:71)
    at org.apache.hadoop.io.serializer.WritableSerialization$WritableDeserializer.deserialize(WritableSerialization.java:42)
    at org.apache.hadoop.mapreduce.task.ReduceContextImpl.nextKeyValue(ReduceContextImpl.java:146)
    at org.apache.hadoop.mapreduce.task.ReduceContextImpl.nextKey(ReduceContextImpl.java:121)
    at org.apache.hadoop.mapreduce.lib.reduce.WrappedReducer$Context.nextKey(WrappedReducer.java:302)
    at org.apache.hadoop.mapreduce.Reducer.run(Reducer.java:170)
    at org.apache.hadoop.mapred.Task$NewCombinerRunner.combine(Task.java:1688)
    at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.sortAndSpill(MapTask.java:1637)
    at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.flush(MapTask.java:1489)
    at org.apache.hadoop.mapred.MapTask$NewOutputCollector.close(MapTask.java:723)
    at org.apache.hadoop.mapred.MapTask.closeQuietly(MapTask.java:2019)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:797)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:341)
    at org.apache.hadoop.mapred.LocalJobRunner$Job$MapTaskRunnable.run(LocalJobRunner.java:243)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
    at java.util.concurrent.FutureTask.run(FutureTask.java:262)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)