Map JSON key-value 到 java 中的 class

Question

I need to map string JSON by key-value into the POJO class, but I'm not sure there is an easier way to convert this.

My class:

class Colors {
    
    private String name;

    private String color;

    public String getName() { return name; }

    public String getColor() { return color; }

}

Example of JSON:

{
    "white": "FFFFFF",
    "red": "FF0000",
    "black": "000000"
}

Is there any way (instead of using foreach loop) to have the above JSON in List<Colors> ?

Ps: I tried some same issue with objectMapper.readValue , but didn't succeed.

Answer 1

You can use com.fasterxml.jackson.annotation.JsonAnySetter annotation which will allow you to handle each key-value pair:

import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.File;
import java.util.ArrayList;
import java.util.List;

public class JsonApp {

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

        ObjectMapper mapper = new ObjectMapper();

        Colors colors = mapper.readValue(jsonFile, Colors.class);
        System.out.println(colors.getColors());
    }
}

class Colors {
    private final List<Color> colors = new ArrayList<>();

    @JsonAnySetter
    public void setAny(String key, String value) {
        colors.add(new Color(key, value));
    }

    public List<Color> getColors() {
        return colors;
    }
}

class Color {

    private String name;
    private String color;

    public Color(String name, String color) {
        this.name = name;
        this.color = color;
    }

    public String getName() {
        return name;
    }

    public String getColor() {
        return color;
    }

    @Override
    public String toString() {
        return "Color{" +
                "name='" + name + '\'' +
                ", color='" + color + '\'' +
                '}';
    }
}

Above code prints:

[Color{name='white', color='FFFFFF'}, Color{name='red', color='FF0000'}, Color{name='black', color='000000'}]

See also:

• Deserializing Jackson by using a key as value

Answer 2

change your json object to:

{
"listcolors": [
    {
        "name": "white",
        "color": "FFFFFF"
    },
    {
        "name": "red",
        "color": "FF0000"
    },
    {
        "name": "black",
        "color": "000000"
    }
]}

your color class should implement serializable

 class Colors implements Serializable {

    private String name;

    private String color;

    public String getName() { return name; }

    public String getColor() { return color; }

}

Now create a list of colors class to receive the deserialization of your object

class ListColors implements Serializable {
    ArrayList<Color> ListColors = new ArrayList<Color>();
}

then:

ListColors objColors = new Gson().fromJson(<
        put your json object string here>, Colors.class);

See more about the GSON library here