@Override
    public void serialize(SystemStreamPartition ssp, JsonGenerator jgen, SerializerProvider provider) throws IOException {
      String sspString = ssp.getSystem() + "." + ssp.getStream() + "." + String.valueOf(ssp.getPartition().getPartitionId());
      jgen.writeFieldName(sspString);
    }
@return Returns a new ObjectMapper that's been configured to (de)serialize
        Samza's job data model, and simple data types such as TaskName,
        Partition, Config, and SystemStreamPartition.
samza-core/src/main/java/org/apache/samza/serializers/model/SamzaObjectMapper.java