Hi Ravijeet,
Behaviour that you describe, is specifics of Jettison JSON processor: for example, if the array consists of only one element, most likely Jettison will not recognize it to be an array, but will qualify it as a complex object with a nested structure.
Regarding custom type converter class. It is not a common practice to make such an enhancement, but considering Jettison employs type converter and can be extended with custom classes and REST adapter calls Jettison for XML/JSON conversion, it is necessary to ensure corresponding developed class is deployed and loaded properly, before or at a time of REST adapter invocation.
Regards,
Vadim