json - Spring Boot : Return a empty JSON instead of empty body when returned object is null

Question

我有一个 RestController ，当我调用该方法时:

@RequestMapping(value = "/sigla/{sigla}")
@ResponseBody
public PaisDTO obterPorSigla(@PathVariable String sigla) {
    return service.obterPorSigla(sigla);
}

如果找到一条记录，我会得到一个很好的 JSON 响应:

{"nome":"Brasil","sigla":"BR","quantidadeEstados":27}

但是当在数据库上没有找到任何东西时， RestController 返回 null 并且我得到一个空的响应，完全空白的主体。

如何显示空 JSON 而不是空白响应？像下面这样:

{}

完整的 Controller :

@RestController
@RequestMapping("/pais")
public class PaisController {

    @Autowired
    private PaisService service;

    @RequestMapping
    public ResponseEntity<List<PaisDTO>> obterTodos() {
        return CreateResponseEntity.getResponseEntity(service.obterTodos());
    }

    @RequestMapping(value = "/sigla/{sigla}", method = RequestMethod.GET, consumes="application/json", produces="application/json")
    public ResponseEntity<PaisDTO> obterPorSigla(@PathVariable String sigla) {
        HttpHeaders headers = new HttpHeaders();
        headers.add("Content-Type", "application/json");
        PaisDTO paisDTO = service.obterPorSigla(sigla);
        if(paisDTO != null) return new ResponseEntity<PaisDTO>(paisDTO, headers, HttpStatus.OK);
        else return new ResponseEntity<PaisDTO>(headers, HttpStatus.OK);
    }

Answer 1

首先，如果您使用的是 @RestController您不需要的注释 @ResponseBody注释，摆脱它。

其次，如果您尝试使用 REST Controller，那么您会遗漏一些东西，请这样做:

@RequestMapping(value = "/sigla/{sigla}", method = RequestMethod.GET, consumes = "application/json", produces="application/json")
public ResponseEntity<PaisDTO> obterPorSigla(@PathVariable String sigla) {
        HttpHeaders headers = new HttpHeaders();
        headers.add("Content-Type", "application/json");    
        PaisDTO paisDTO = service.obterPorSigla(sigla);
        if(paisDTO != null) return new ResponseEntity<>(paisDTO, headers, HttpStatus.OK);
        else return new ResponseEntity<>(headers, HttpStatus.OK); 
}

在上面的示例中，如果您将获得 null，那么您将返回一个空的响应 JSON。