为什么 spring 启动中的 POST 请求出现 Postman 错误“不支持的媒体类型”

Question

我有一个实体 class State扩展了抽象 class Location并实现了它的抽象方法。 当我在 postman 上发出PostMapping请求并将内容类型设置为 Json 时，我收到一个错误不支持的媒体类型，如下所示：

"error:" Unsupported Media Type,
"trace": org.springframework.web.HttpMediaTpeNotSupportedException:Content type:'application/json;...

摘要 class：

@MappedSuperclass
public abstract class Location {
@Id
@Column(name="id")
@GeneratedValue(strategy= GenerationType.IDENTITY)
private Integer id;

@Column(name = "long")
private String longitude;

@Column(name = " lat")
private String latitude;

public Location (){}
//assessors & mutators ommited with abstract methods
}

具体State实体class：

@Table(name="State")
public class State extends Location {

@Pattern(regexp = "[0-9]{5}")
private String sateCode;

@JsonManagedReference
@OneToOne(mappedBy="state",
cascade=CascadeType.All, fetch=FetchType.Lazy)
private City city = new City();
//constructors & other implementations omitted

@Override
public void setCity(String city){
this.city=city
}

public void setStateCode(String code){
this.stateCode = stateCode;
}
///getter omitted
}

具体城市实体class：

@Table(name = "City");
public class City extends Location {

@JsonBackReference
@OneToOne(cascade={
CascadeType.DeTACH, CascadeType. MERGE})
@JoinColumn(name = "state_city_id")
private State state;

//constructors & other implementations omitted
@Override
public void setState(State state) {
this.state=state;
}
}
}

Controller：

@Controller
@RequestMapping(path = "location/destination")
public class LocationController{ 
     @Autowired
    @Qualifier("stateImpl")
    private LocationService service;
    @PostMapping(value = "/state", consumes = org.springframework.http.MediaType.APPLICATION_JSON_VALUE, produces = org.springframework.http.MediaType.APPLICATION_JSON_VALUE)
    public void save( @Valid @RequestBody State s ,BindingResult theBindingResult,
            HttpServletResponse r) throws IOException{
    if(theBindingResult.hasErrors()) {
            throw new InputException("Wrong data input!");
        }
        service.save(s);
        r.sendRedirect("");
    }
@GetMapping()
public ResponseEntity<Object>findAll(){
return new ResponseEntity<Object>(service.findAll(),HttpStatus.OK);
}
}

postman 上的错误消息：

"status": 415,
    "error": "Unsupported Media Type",
    "trace": "org.springframework.web.HttpMediaTypeNotSupportedException: Content type 'application/json;charset=UTF-8 not supported\r\n\tat...'

Answer 1

当我更改State实体 class 中的city字段时，代码有效：

@Entity
@Table(name="State")
public State extends Location {

@JsonBackReference
@OneToOne(mappedBy="state",
cascade=CascadeType.All, fetch=FetchType.Lazy)
private City city = new City();
}

City实体中的state字段如下所示：

@Entity
@Table(name="City")
public class City extends Location {
@JsonManagedReference
@OneToOne(cascade={
CascadeType.DeTACH, CascadeType. MERGE})
@JoinColumn(name = "state_city_id")
private State state;
}
```.
Though I'm yet to understand what really happened behind the scenes.