Untitled

@RestController
public class CandidatosWS {

    @Autowired
    CandidatoService candidatoService;

    @RequestMapping(value = "/candidatos/", method = RequestMethod.GET)
    public ResponseEntity<List<Candidato>> allCandidatos() {
        List<Candidato> listCandidatos = null;

        try {
            listCandidatos = candidatoService.listarCandidatos();
        } catch (Exception e) {
            e.printStackTrace();
        }

        return new ResponseEntity<List<Candidato>>(listCandidatos, HttpStatus.OK);
    }
}

<html>
    <head>
        <title>Error</title>
    </head>
    <body>Not Acceptable</body>
</html>

@RequestMapping(value = "/candidatos/", method = RequestMethod.GET)

@RequestMapping(value = "/candidatos/", method = RequestMethod.GET, produces=MediaType.APPLICATION_JSON_VALUE)

List<JSONObject> listCandidatos = new ArrayList<JSONObject>();

return new ResponseEntity<List<JSONObject>>(listCandidatos, HttpStatus.OK);

@RequestMapping(value = "/candidatos/", method = RequestMethod.GET, produces=MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<List<Candidato>> allCandidatos() {

    List<Candidato> listCandidatos = /* busca de candidatos*/

    List<JSONObject> listCandidatosJson = new ArrayList<JSONObject>();
    for (Candidato cand : listCandidatos ) {
        JSONObject candidatoJson = cand.toJson(); //implemente o método toJson(), conforme sugerido
        listCandidatosJson.add(candidatoJson);
    }

    return new ResponseEntity<List<JSONObject>>(listCandidatosJson, HttpStatus.OK);
    }
}