public synchronized boolean next(LongWritable key,
                                     Text value) throws IOException {
      boolean result = super.next(key, value);
      if (result) {
        System.out.println("Read " + value);
        rot13(value.getBytes(), 0, value.getLength());
        System.out.println("Returned " + value);
      }
      return result;
    }
A simple input format that does a rot13 on the inputs
itests/util/src/main/java/org/apache/hadoop/hive/ql/io/udf/Rot13InputFormat.java