傑克遜，序列化參考的一個屬性

Question

序列化具有其他對象引用的Java對象時，我只需要序列化嵌套對象的一個​​屬性（通常是外鍵的情況，因此序列化對象引用的“id”屬性）。 其他一切。

例如，我有兩個類，我需要序列化為JSON和XML（為清楚起見，刪除了JPA注釋）：

關系：用戶 - >（一對多）地址信息; 另外：AddressInformation - >（一對一）用戶

@XmlRootElement
public class User {
    private String id;
    private String firstName;
    private String lastName;
    private String email;
    private AddressInformation defaultAddress;
    private Set<AddressInformation> addressInformation;

    public User() {
    }

    @JsonProperty(value = "id")
    @XmlAttribute(name = "id")
    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    @JsonProperty(value = "firstname")
    @XmlAttribute(name = "firstname")
    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    @JsonProperty(value = "lastname")
    @XmlAttribute(name = "lastname")
    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    @JsonProperty(value = "email")
    @XmlAttribute(name = "email")
    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    @JsonIgnore
    public Set<AddressInformation> getAddressInformation() {
        return addressInformation;
    }

    public void setAddressInformation(Set<AddressInformation> addressInformation) {
        this.addressInformation = addressInformation;
    }

    @JsonProperty(value = "defaultaddress")
    @JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
    public AddressInformation getDefaultAddress() {
        return defaultAddress;
    }

    public void setDefaultAddress(AddressInformation defaultAddress) {
        this.defaultAddress = defaultAddress;
    }
}

地址信息：

@XmlRootElement
public class AddressInformation  {
    private String id;
    private String address;
    private String details;
    private User user;

    @JsonProperty(value = "id")
    @XmlAttribute(name = "id")
    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    @JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    @JsonProperty(value = "details")
    @XmlAttribute(name = "details")
    public String getDetails() {
        return details;
    }

    public void setDetails(String details) {
        this.details = details;
    }

    @JsonProperty(value = "address")
    @XmlAttribute(name = "address")
    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public AddressInformation() {
        super();
    }
}
enter code here

例如，在序列化用戶時，我需要：

{
  "id" : "idofuser01",
  "email" : "some.email@gmail.com",
  "status" : "OK",
  "firstname" : "Filan",
  "lastname" : "Ovni",
  "defaultaddressid" : "idofaddress01",
}
enter code here

序列化AddressInformation時：

{
  "id" : "idofaddress01",
  "address" : "R.8. adn",
  "details" : "blah blah",
  "userid" : "idofuser01",
}

我試過@JsonManageReference和@JsonBackReference沒有成功。 如你所見，我也試過@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")

Answer 1

剛剛找到了使用Jackson 2.1+的方法。

使用（這將僅選擇AddressInformation的id屬性）注釋對象引用：

@JsonProperty(value = "defaultaddressid")
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
@JsonIdentityReference(alwaysAsId = true) 
public AddressInformation getDefaultAddress() {
    return defaultAddress;
}

序列化工作得很好。

Answer 2

您可以為此類實現自定義反序列化器，並在User類中使用它。 示例實現：

class AddressInformationIdJsonSerializer extends JsonSerializer<AddressInformation> {
    @Override
    public void serialize(AddressInformation value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
        jgen.writeString(value.getId());
    }
}

並在User類中配置：

@JsonProperty(value = "defaultaddress")
@JsonSerialize(using = AddressInformationIdJsonSerializer.class)
public AddressInformation getDefaultAddress() {
    return defaultAddress;
}

###實現一個接口的所有類的通用解決方案###
您可以創建包含String getId()方法的接口：

interface Identifiable {
    String getId();
}

此接口的Serializer可能如下所示：

class IdentifiableJsonSerializer extends JsonSerializer<Identifiable> {
    @Override
    public void serialize(Identifiable value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
        jgen.writeString(value.getId());
    }
}

現在，您可以將此序列化程序用於所有可Identifiable實現。 例如：

@JsonProperty(value = "defaultaddress")
@JsonSerialize(using = IdentifiableJsonSerializer.class)
public AddressInformation getDefaultAddress() {
    return defaultAddress;
}

當然： AddressInformation必須實現這個接口：

class AddressInformation implements Identifiable {
    ....
}