How to parse JSON element that can be either simple string or an object into Class Object

Question

I am not able to unmarshall a JSON key which can hold either a string value or an another JSON Object using Jackson Library.

Ex:- Below are the two possible values.

1)

"ProviderData": {
    "INVALID": "HEX",
    "#text": "Sample"
}

2)

"ProviderData": "1C"

Could someone please verify and suggest me on this issue.

Do you have two different java objects to map, or how does the object look like? — Samuel Philipp, May 28 '19 at 16:32
In case there is a `String` - `1C`, what does it mean? Is it `INVALID` or `#text` value? — Michał Ziober, May 28 '19 at 18:48

score 0 · Answer 1 · answered May 28 '19 at 16:12

you could deserialize to JsonNode and then extract the contents individually, or deserialize to an Object and use instanceof to determine if it's a Map or another type, or use a custom deserializer to unpack the data into a custom object that handles both cases.

score 0 · Accepted Answer · answered May 28 '19 at 19:02

You can write custom deserialiser and handle these both cases or write two constructors for ProviderData POJO class and properly use JsonCreator and JsonCreator annotations. See below example:

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.File;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        ObjectMapper mapper = new ObjectMapper();

        System.out.println(mapper.readValue(jsonFile, Response.class));
    }
}

class Response {

    @JsonProperty("ProviderData")
    private ProviderData data;

    // getters, setters, toString
}

class ProviderData {

    private static final String INVALID_NAME = "INVALID";
    private static final String TEXT_NAME = "#text";

    @JsonProperty(INVALID_NAME)
    private final String invalid;

    @JsonProperty(TEXT_NAME)
    private final String text;

    @JsonCreator(mode = JsonCreator.Mode.DELEGATING)
    public ProviderData(String invalid) {
        this(invalid, null);
    }

    @JsonCreator
    public ProviderData(@JsonProperty(INVALID_NAME) String invalid, @JsonProperty(TEXT_NAME) String text) {
        this.invalid = invalid;
        this.text = text;
    }

    // getters, toString
}

For this JSON payload:

{
  "ProviderData": {
    "INVALID": "HEX",
    "#text": "Sample"
  }
}

Above example prints:

Response{data=ProviderData{invalid='HEX', text='Sample'}}

And for String primitive JSON payload:

{
  "ProviderData": "1C"
}

Above example prints:

Response{data=ProviderData{invalid='1C', text='null'}}

As you can see, JSON Object is mapped properly using 2-arg constructor and String primitive is mapped using 1-arg constructor and we assume that this value means invalid key from JSON Object example.

How to parse JSON element that can be either simple string or an object into Class Object

2 Answers2