映射值中的java类型不匹配：应为组织。阿帕奇。hadoop。木卫一。可空写，接收组织。阿帕奇。hadoop。木卫一。文本

Question

我正试图调整现有的问题以满足我的需要

基本上输入是简单的文本 我处理它并将键/值对传递给reducer 我创建了一个json。。所以有关键，但没有价值 所以地图绘制者：

输入：文本/文本

输出：文本/文本

减缩器：文本/文本

输出：文本/无

我的签名如下：

public class AdvanceCounter {
/**
 * The map class of WordCount.
 */
public static class TokenCounterMapper
    extends Mapper<Object, Text, Text, Text> { // <--- See this signature

   public void map(Object key, Text value, Context context) // <--- See this signature
        throws IOException, InterruptedException {

     context.write(key,value); //both are of type text OUTPUT TO REDUCER
    }
}
   public static class TokenCounterReducer
    extends Reducer<Text, Text, Text, **NullWritable**> { // <--- See this signature Nullwritable here
    public void reduce(Text key, Iterable<Text> values, Context context) // <--- See this signature
        throws IOException, InterruptedException {


        for (Text value : values) {
            JSONObject jsn = new JSONObject();
            //String output = "";
            String[] vals = value.toString().split("\t");
            String[] targetNodes = vals[0].toString().split(",",-1);
            try {
                jsn.put("source",vals[1]);
                jsn.put("targets",targetNodes);
                context.write(new Text(jsn.toString()),null); // no value 
            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }


    }
}
public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
    Job job = new Job(conf, "Example Hadoop 0.20.1 WordCount");

    // ...
    //
    job.setOutputValueClass(NullWritable.class);
    FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
    FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
}

}

但在执行时，我得到了以下错误：

13/06/04 13:08:26 INFO mapred.JobClient: Task Id : attempt_201305241622_0053_m_000008_0, Status : FAILED
java.io.IOException: Type mismatch in value from map: expected org.apache.hadoop.io.NullWritable, recieved org.apache.hadoop.io.Text
    at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.collect(MapTask.java:1019)
    at org.apache.hadoop.mapred.MapTask$NewOutputCollector.write(MapTask.java:691)
    at org.apache.hadoop.mapreduce.TaskInputOutputContext.write(TaskInputOutputContext.java:80)
    at org.sogou.Stinger$TokenCounterMapper.map(Stinger.java:72)
    at org.sogou.Stinger$TokenCounterMapper.map(Stinger.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.Child$4.run(Child.java:255)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:396)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1093)
    at org.apache.hadoop.mapred.Child.main(Child.java:249)

Answer 1

您还没有指定映射输出类型，所以它与您为reducer设置的类型相同，分别是Text和NullWritable，这对映射器来说是不正确的。您应该执行以下操作以避免任何混淆，最好为mapper和reducer指定所有类型：

job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(Text.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(NullWritable.class);