json - Jackson2 多对多反序列化

Question

我有两个类 Events 和 Users，它们具有多对多关系。

public class Event {

    private int id;

  private List<Users> users;
}

public class User {
        private int id;

      private List<Event> events;
}

我已阅读 @JsonIdentityInfo 注释应该有所帮助，但我看不到这方面的示例。

Answer 1

您可以使用 @JsonIdentityInfo在两个类User和 Event这样:

import java.util.List;

import com.fasterxml.jackson.annotation.JsonIdentityInfo;
import com.fasterxml.jackson.annotation.ObjectIdGenerators;

@JsonIdentityInfo(generator = ObjectIdGenerators.UUIDGenerator.class, property="@UUID")
public class User
{
    private int id;
    private List<Event> events;

    // Getters and setters
}

...和

import java.util.List;

import com.fasterxml.jackson.annotation.JsonIdentityInfo;
import com.fasterxml.jackson.annotation.ObjectIdGenerators;

@JsonIdentityInfo(generator = ObjectIdGenerators.UUIDGenerator.class, property="@UUID")
public class Event
{
    private int id;
    private List<User> users;

    // Getters and setters
}

您可以使用 <a href="http://fasterxml.github.io/jackson-annotations/javadoc/2.2.0/com/fasterxml/jackson/annotation/ObjectIdGenerator.html" rel="noreferrer noopener nofollow">ObjectIdGenerator</a> 中的任何一个视情况而定。现在，多对多映射对应的对象的序列化和反序列化就成功了:

public static void main(String[] args) throws IOException
{
    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.configure(SerializationFeature.INDENT_OUTPUT, true);

    Event event1 = new Event();
    event1.setId(1);
    Event event2 = new Event();
    event2.setId(2);

    User user = new User();
    user.setId(10);

    event1.setUsers(Arrays.asList(user));
    event2.setUsers(Arrays.asList(user));
    user.setEvents(Arrays.asList(event1, event2));

    String json = objectMapper.writeValueAsString(user);
    System.out.println(json);

    User deserializedUser = objectMapper.readValue(json, User.class);
    System.out.println(deserializedUser);
}

希望这对您有所帮助。