反序列化与杰克逊参照现有对象

Question

JSON

{ 
    "schools": [ 
    { 
     "id": 1, 
     "name": "School A" 
    }, 
    { 
     "id": 2, 
     "name": "School B" 
    } 
    ], 
    "students": [ 
    { 
     "id": 1, 
     "name": "Bobby", 
     "school": 1 
    } 
    ] 

} 

如何将我的JSON映射到以下类，鲍比的学校被映射到已实例化的学校A.

public class School { 
    private Integer id; 
    private String name; 
} 

public class Student { 
    private Integer id; 
    private String name; 
    private School school; 
} 

我试过一些奇怪的东西与学生类...

public class Student { 
    private Integer id; 
    private String name; 
    private School school; 

    @JsonProperty("school") 
    public void setSchool(Integer sid) { 
    for (School school : getSchools()) { 
     if (school.id == sid) { 
     this.school = school; 
     break; 
     } 
    } 
    } 
} 

问题我很喜欢因为学校和学生都在同一时间从JSON中解析出来，所以我不确定如何获得学校名单。也许我应该分开解析这些，所以我先列出学校名单？

Answer 1

杰克逊会为你做。只需用@JsonIdentityInfo注释您的对象：

@JsonIdentityInfo(scope=School.class, generator=ObjectIdGenerators.PropertyGenerator.class, property="id") 
public class School { 
    private Integer id; 
    private String name; 

    public School() { 
    } 

    public School(Integer id, String name) { 
     this.id = id; 
     this.name = name; 
    } 

    public Integer getId() { 
     return id; 
    } 

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

    public String getName() { 
     return name; 
    } 

    public void setName(String name) { 
     this.name = name; 
    } 
} 

@JsonIdentityInfo(scope=Student.class, generator=ObjectIdGenerators.PropertyGenerator.class, property="id") 
public class Student { 
    private Integer id; 
    private String name; 
    private School school; 

    public Student() { 
    } 

    public Student(Integer id, String name, School school) { 
     this.id = id; 
     this.name = name; 
     this.school = school; 
    } 

    public Integer getId() { 
     return id; 
    } 

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

    public String getName() { 
     return name; 
    } 

    public void setName(String name) { 
     this.name = name; 
    } 

    public School getSchool() { 
     return school; 
    } 

    public void setSchool(School school) { 
     this.school = school; 
    } 
} 

public static void main(String[] args) throws IOException { 
    School school = new School(1, "St Magdalene's"); 
    Student mary = new Student(1, "Mary", school); 
    Student bob = new Student(2, "Bob", school); 
    Student[] students = new Student[] {mary, bob}; 

    // Write out 
    String serialized = mapper.writeValueAsString(students); 
    System.out.println("Serialized: " + serialized); 
    // Read in 
    Student[] deserialized = mapper.readValue(serialized, Student[].class); 
}