将嵌套的 Java 对象序列化为 json

Question

There is a java object that refers to another object, and that object refers to another one. All these three objects can be serialized into json.

All classes have appropriate Jackson annotation:

@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.NONE, getterVisibility = JsonAutoDetect.Visibility.ANY, setterVisibility = JsonAutoDetect.Visibility.NONE)
@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonIgnoreProperties(ignoreUnknown = true)
class A {
    B b;
    @JsonProperty("components")
    public String getComponents() {
       /***/
    }
}

@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY, getterVisibility = JsonAutoDetect.Visibility.NONE, setterVisibility = JsonAutoDetect.Visibility.NONE)
@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonIgnoreProperties(ignoreUnknown = true)
class B {
   @JsonProperty 
   String message;
   @JsonProperty
   Long id;
   @JsonIgnore
   C c;
}

@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY, getterVisibility = JsonAutoDetect.Visibility.NONE, setterVisibility = JsonAutoDetect.Visibility.NONE)
@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonIgnoreProperties(ignoreUnknown = true)
Class C {
   @JsonProperty 
   String param1;
   @JsonProperty
   String param2;
}

Currently the getComponents method in class A looks like this:

    public String getComponents() {
         JSONObject components = new JSONObject();
         components.put("b", b);
         components.put("c", c);
         return components.toString();
    }

For components property I expect to see the following in the json:

"components": { "b": {"message":"", id:1}, "c": {"param1":"", "param2":""}}

But currently it returns the reference to the objects

"components": { "b": "com.myproject.B@6by789ae", "c": "com.myproject.C@8io287ko"}

Considering that each object has the ability to be turned into json, why doesn't JSONObject.toString recursively loop over them and turn each into its json representation? Is there any mechanism that I use?

Answer 1

Ok. I think I found a solution. I turned components from JSONObject into Map<String, Object> and jackson seems to be handling the rest:

public Map<String, Object> getComponents() {
     Map<String, Object> components = new HashMap<>();
     components.put("b", b);
     components.put("c", c);
     return components;
}