How get fields of object in parameter iReport

I'm passing the object "OrdemServico" as parameter to report.

OrdemServico ordemServico = new OrdemServico();  
ordemServico.setCodigo("CA123");
mapa.put("ORDEMSERVICO", ordemServico);

And on the .jrxml i added a parameter with same name of the parameter in map. how i can get the fields of the object? Tnks