code: public static void setSerializations(Configuration conf) {
  		String serializations = conf.get(HADOOP_IO_SERIALIZATIONS);
  
  		LinkedList<String> list = new LinkedList<String>();
  
  		if(serializations != null && !serializations.isEmpty())
  			Collections.addAll(list, serializations.split(","));
  
  		// required by MultiInputSplit
  		String writable = WritableSerialization.class.getName();
  		String tuple = TupleSerialization.class.getName();
  
  		list.remove(writable);
  		list.remove(tuple);
  
  		list.addFirst(writable);
  		list.addFirst(tuple);
  
  		// make writable last
  		conf.set(HADOOP_IO_SERIALIZATIONS, Util.join(list, ","));
  	}
docs: Like in Cascading's TupleSerialization.setSerializations() but accepting a Hadoop's Configuration rather than JobConf.