如何將 ResponseEntity 設置為 Spring MVC 4 的 HTTP 404

Question

我正在使用 Java 1.7 和 Spring 4 MVC 創建一個 Rest Controller，但如果我的 dao 返回一個空結果，則需要它返回一個 HTTP 404 ResponseEntity。

pom.xml:

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-webmvc</artifactId>
        <version>4.0.3.RELEASE</version>
    </dependency>

休息控制器：

@RestController
@RequestMapping("/orders")
public class OrderController {

    private final OrderDao dao;
    private HttpHeaders headers = null;

    @Autowired
    public OrderController(OrderDAO dao) {
        this.dao = dao;
        headers = new HttpHeaders();
        headers.add("Content-Type", "application/json");
    }

    @RequestMapping(value = "{orderId}/{productId}", method = RequestMethod.GET, produces = "APPLICATION/JSON")
    public ResponseEntity<Object> getOrderDetails(@PathVariable("orderId") String orderId, 
                                                  @PathVariable("productId") String productId) {

        return new ResponseEntity<Object>(dao.getOrderDetails(orderId,productId), headers, HttpStatus.OK);
    }   
}

如何設置以便如果 dao.getOrderDetails(orderId,productId) 為空，它應該為訪問此 Rest Call 的客戶端程序返回 HTTP 404？

試過這個：

    ResponseEntity<Object> response = new ResponseEntity<Object>(dao.getOrderDetails(orderId,productId), headers, HttpStatus.OK);
    if (response == null) {
        return new ResponseEntity<Object>(HttpStatus.NOT_FOUND);
    }
    return response;

但是 Eclipse 說這個 if 子句是“死代碼”......

Answer 1

是死代碼，因為response變量永遠不會為null 。 試試這個：

Object data = dao.getMlsPlayerSeasonStats(profileId,sportsTeamId);// I don´t know the DAO operation return type
if (data == null) {
    return new ResponseEntity<Object>(HttpStatus.NOT_FOUND);
}
return new ResponseEntity<Object>(data, headers, HttpStatus.OK);;