将Json映射到嵌套POJO

Question

I've the following JSON from some upstream api

{
    "Id": "",
    "Name": "",
    "Age": ""
}

And I need to map this above json to a downstream request paylaod (POJO) .

public class Employee
{
     @JsonProperty("Id")
     private Integer Id;
     private User user;
}

public class User {

     @JsonProperty("Name")
     private String name;

     @JsonProperty("Age")
     private String age;

}

Right now I'm doing something like

Employee employee = new ObjectMapper().treeToValue(JsonNode node,Employee.class);

But this is giving null in User Object.

The challenge here is , that the json we are getting from upstream can't be changed . So , is there is any way to map the fields into the nested User object , without changing the structure of json received from upstream.

One Solution is : map the fields separately into User object and then set it into the Employee object . But that's not an efficient solution , because for null validations we would need to do validations separately for User and Employee objects. If the nesting is complex then , validation will be hell of replicated code .

Answer 1

Your JSON does not comply with your Employee class.

Because name and age is at the same level as id , but you want to wrapped in a class User .

So either:

1. Change the json the structure to

     { "id": "", "user": { "name": "", "age": "" } } 

Or

2. Unwrap the User class, the Employee class will be:

     public class Employee { @JsonProperty("Id") private Integer Id; @JsonProperty("Name") private String name; @JsonProperty("Age") private String age; } 

Edit

If you can't choose either option 1 or 2, you have only one option left is to create custom deserializer:

Write a deserializer:

public class EmployeeDeserializer extends StdDeserializer<Item> { 

    public EmployeeDeserializer() { 
        this(null); 
    } 

    public EmployeeDeserializer(Class<?> vc) { 
        super(vc); 
    }

    @Override
    public Employee deserialize(JsonParser jp, DeserializationContext ctxt) 
      throws IOException, JsonProcessingException {
        JsonNode node = jp.getCodec().readTree(jp);
        int id = (Integer) ((IntNode) node.get("Id")).numberValue();
        String name = node.get("Name").asText();
        String age = node.get("Age")).asText();
        User user = new User(name, age);
        return new Employee(id, user);
    }
}

Then register this deserializer:

ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addDeserializer(Employee.class, new EmployeeDeserializer());
mapper.registerModule(module);

Employee readValue = mapper.readValue(json, Employee.class);

Another way to register deserializer is:

@JsonDeserialize(using = EmployeeDeserializer.class)
public class Employee {

Answer 2

It seems you are not nesting your JSON correctly. Or your Object Structure is wrong.

JSON should be:

{
    "Id": "",
    "user" : {
                "Name": "",
                "Age": ""
    }
}

Answer 3

The json structure does not match the structure of your classes. if the json was like;

{
  "Id": "an-id,
  "user": {
    "Name": "Joe",
    "Age": "21"
  }
}

Then your code to deserialise to an Employee object would work.