反序列化JSON從休眠

Question

我在德春啓動反序列化類的問題。當我的控制器試圖反序列化它時，它會崩潰。這裏是類：

@Entity 
@Table(name="trash_cans") 
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property="id") 
public class TrashCan { 
    @Id 
    @GeneratedValue(strategy=GenerationType.AUTO) 
    @Column(name="TRASH_CAN_ID") 
    long id; 

    @Column(name="TRASH_CAN_NAME") 
    String name; 

    @ManyToOne 
    @JoinColumn(name="PLACE_ID") 
    private Place place; 

    @OneToMany(mappedBy="trashCan", targetEntity=TrashMeter.class, fetch=FetchType.LAZY) 
    private List<TrashCan> trashMeterList; 

    @OneToMany(mappedBy="trashCan", targetEntity=TrashSensor.class, fetch=FetchType.LAZY) 
    private List<TrashSensor> trashSensorList; 

    public TrashCan() {  
    } 

    public TrashCan(long id, String name) { 
     super(); 
     this.id = id; 
     this.name = name; 
    } 

    [getters and setters] 
} 

這取決於這一個：

@Entity 
@Table(name="trash_sensor") 
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property="id") 
public class TrashSensor { 

    @Id 
    @Column(name="id") 
    @GeneratedValue(strategy=GenerationType.AUTO) 
    private long id; 

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

    @Column(name="description") 
    private String description; 

    @ManyToOne 
    @JoinColumn(name="TRASH_CAN_ID") 
    private TrashCan trashCan; 

    @OneToMany(mappedBy = "trashSensor", targetEntity = Measurement.class, fetch = FetchType.LAZY) 
    private List<Measurement> measurementList; 

    public TrashSensor() { 
     super(); 
    } 

和垃圾傳感器取決於這個類：

@Entity 
@Table(name="measurement") 
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property="id") 
public class Measurement { 

    @Id 
    @Column(name="id") 
    @GeneratedValue(strategy=GenerationType.AUTO) 
    private long id; 

    @Column(name="value") 
    private float value; 

    @Column(name="last_measure") 
    private LocalDateTime dateTime; 

    @ManyToOne 
    @JoinColumn(name="trash_sensor_id") 
    private TrashCan trashSensor; 

    public Measurement() { 
    } 

} 

我的Controler：

@RequestMapping(value="/trashCan", method=RequestMethod.GET) 
    public ResponseEntity<Iterable<TrashCan>> getPlaces(){ 
     Iterable<TrashCan> trashCanIterable = trashCansRepository.findAll(); 

     return new ResponseEntity<>(trashCanIterable, HttpStatus.OK); 
    } 

當我打電話給web服務時，我得到這個呃ROR：

Failed to write HTTP message: org.springframework.http.converter.HttpMessageNotWritableException: Could not write content: could not deserialize (through reference chain: java.util.ArrayList[0]-br.com.simplepass.cleanerway.domain.TrashCan["trashSensorList"]-org.hibernate.collection.internal.PersistentBag[0]-br.com.simplepass.cleanerway.domain.TrashSensor["measurementList"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: could not deserialize (through reference chain: java.util.ArrayList[0]-br.com.simplepass.cleanerway.domain.TrashCan["trashSensorList"]-org.hibernate.collection.internal.PersistentBag[0]-br.com.simplepass.cleanerway.domain.TrashSensor["measurementList"])

我無法解釋這個錯誤=/。任何有關這個問題的幫助非常感謝。當您使用實體之間的關係

@OneToMany(mappedBy = "trashSensor", targetEntity = Measurement.class, fetch = FetchType.LAZY) 
@JsonIgnore 
private List<Measurement> measurementList; 

Answer 1

你是因爲你的JSON是進入一個循環，來避免這種情況，使用@JsonIgnore註解收到此錯誤。想象一下，您的垃圾箱已鏈接到垃圾桶。而你的垃圾鏈接到它的包裝 - 垃圾桶。所以你試圖序列化TrashCan實體，你也要序列化垃圾桶。然後當你正在序列化垃圾桶時，垃圾桶再次被序列化。等等。這是一個循環。您可以在每個可能導致循環的實體上使用@JsonIgnore。

@JsonIgnore 
@ManyToOne 
@JoinColumn(name="PLACE_ID") 
private Place place; 

@JsonIgnore 
@OneToMany(mappedBy="trashCan", targetEntity=TrashMeter.class, fetch=FetchType.LAZY) 
private List<TrashCan> trashMeterList; 

@JsonIgnore 
@OneToMany(mappedBy="trashCan", targetEntity=TrashSensor.class, fetch=FetchType.LAZY) 
private List<TrashSensor> trashSensorList; 

但這是一個壞方法。強烈建議爲序列化/反序列化使用DTO（數據傳輸對象）模式。它也給你更多的靈活性。如果您需要trashMeterList和trashSensorList響應然後按照這個答案你可以閱讀一下here

Answer 2

它發生：

Answer 3

。

由於休眠延遲加載，無會話，而deserialisation，你得到這個例外。

要解決只是改變你的控制器：

@RequestMapping(value="/trashCan", method=RequestMethod.GET) 
    public ResponseEntity<Iterable<TrashCan>> getPlaces(){ 
     Iterable<TrashCan> trashCanIterable = trashCansRepository.findAll(); 
     List<TrashCan> responseList = new ArrayList<TrashCan>(trashCanIterable.size()) 
     while(trashCanIterable.hasNext()){ 
      TrashCan trashCan = trashCanIterable.next(); 
      for(TrashMeter trashMeter : trashCan.trashMeterList){ 

      } 
      for(TrashSensor trashSensor : trashCan.trashSensorList){ 

      } 
      responseList.add(trashCan); 
     } 
     return new ResponseEntity<>(responseList, HttpStatus.OK); 
    }