求mr读取parquet的例子

按照
http://blog.cloudera.com/blog/2014/03/how-to-use-parquet-with-impala-hive-pig-mapreduce/ 里的例子貌似有问题，出来的是所有的的key:value数据。
比如有parquet源表里有字段a和b，这个例子最后出来的是
a:1
b:2
如果
   public void map(LongWritable key, Group value, Context context) throws IOException, InterruptedException {
      NullWritable outKey = NullWritable.get();
      String outputRecord = "";
      // Get the schema and field values of the record
      String inputRecord = value.toString();
      // Process the value, create an output record
      // ...
      context.write(outKey, new Text(outputRecord));
   }