Question 214497 in Json Question posted in
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Unable to convert JSON Array into a List in Java

I have an issue in converting JSONArray into a List using Jackson Object Mapper.

public class Main {

public static void main(String[] args) throws Exception {
    String test = Files.readString(Path.of("test.json"));
    callRequired(test);
}

public static void callRequired(String test) {
    ObjectMapper mapper = new ObjectMapper();
    try {
        List<Condition> result = mapper.readerForListOf(Condition.class).readValue(test.trim());
        System.out.println(result);
    } catch (JsonMappingException e) {
        e.printStackTrace();
    } catch (JsonProcessingException e) {
        e.printStackTrace();
    }
}

}

The test.json is:

{
    "condition": [
        {
            "type": "NONE",
            "subConditons": [
                {
                    "type": "NONE",
                    "subConditions": []
                },
                {
                    "type": "AND",
                    "subConditions": [
                        {
                            "type": "NONE",
                            "subConditions": []
                        }
                    ]
                }
            ]
        },
        {
            "type": "OR",
            "subConditions": []
        }
    ]
}

The Condition class is as follows:

public class Condition {
Type type = Type.NONE;
List<Condition> subConditions;

public Condition() {
    
}

public Condition(Type type, List<Condition> subConditions) {
    this.type = type;
    this.subConditions = subConditions;
}

public List<Condition> getSubConditions() {
    return subConditions;
}

public void setSubConditions(List<Condition> subConditions) {
    this.subConditions = subConditions;
}

public Type getType() {
    return type;
}

public void setType(Type type) {
    this.type = type;
}

public enum Type {
    NONE,
    AND,
    OR;
}

@Override
public String toString() {
    return "Condition [type=" + type + ", subConditions=" + subConditions + "]";
    }
}

Edit: The Condition array contains a list of conditions within which lies a subCondition which is also a type of Condition.

EDIT: Thanks, I have added the requisite braces and checked for its validity. I have also added an all args construcutor and a no args constructor as well.

How do I change the JSON so that I receive a List of conditions with the proper subconditions nested with Jackson.

Tags:

2

Answers


  1. 0

    In your JSON, the "condition" object starts with a "[", setting its type to an array. This isn’t how your condition object class look like.

    It should be more like:

    [
    {
        "type" : "NONE",
        "subConditions" : []
    }
]
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  2. 0

    If you have no objection to switching to Gson, here is a basic parse.

    String test = Files.readString(Path.of("test.json"));
Gson gson = new Gson();
JsonElement element = gson.fromJson(test, JsonObject.class).get("condition");
List<Condition> conditions = Arrays.asList(gson.fromJson(element, Condition[].class));

    class Condition {
    Type type;
    List<Condition> subConditions;

    @Override
    public String toString() {
        return "(%s, %s)".formatted(type, subConditions);
    }
}

enum Type {
    NONE, AND, OR
}

    Output

    (NONE, [(NONE, []), (AND, [(NONE, [])])])
(OR, [])
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