Convert Map to JSON in Java

Question

I'm migrating from node to java and finding really difficult to work with JSON I have the following Map structure:

{1=Terrain, 2=Tree, 3=Building}

Which I need to transform into JSON, but with this strcutre:

[{ id: 1, name: Terrain }, { id: 2, name: Tree }, { id: 3, name: Building }]

How can I achieve that? Thanks

score 1 · Answer 1 · answered Oct 14 '21 at 13:18

Assuming your map is of type Map<Integer,String>, you can define the following class:

public class IdName {
    private final int id;
    private final String name;

    public IdName(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }
}

You will then want to convert your map into a collection of IdNames:

        List<IdName> list = map.entrySet().stream()
                .map((e)->new IdName(e.getKey(),e.getValue()))
                .collect(Collectors.toList());

and then convert that collection to JSON. Example with Jackson:

String json = mapper.writeValueAsString(list);

score 0 · Answer 2 · answered Oct 14 '21 at 13:14

Multiple APIs available for Map to JSON converter

Using Jackson API
Using Gson API
Using org.json API

For Jackson API

For that you need to add jakson dependencies in project

<dependencies>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
     <artifactId>jackson-core</artifactId>
    <version>2.9.8</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.8</version>
</dependency>
</dependencies>

Please look into following Main program for conversation

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.jupiter.api.Test;
import java.util.HashMap;
import java.util.Map;

public class ConvertJavaMapToJson {

@Test
public void convertMapToJson() {
    Map<String, String> elements = new HashMap();
    elements.put("Key1", "Value1");
    elements.put("Key2", "Value2");
    elements.put("Key3", "Value3");

    ObjectMapper objectMapper = new ObjectMapper();

    try {
        String json = objectMapper.writeValueAsString(elements);
        System.out.println(json);
    } catch (JsonProcessingException e) {
        e.printStackTrace();
    }
  }
}

For Gson

<dependencies>
   <dependency>
      <groupId>com.google.code.gson</groupId>
      <artifactId>gson</artifactId>
      <version>2.8.5</version>
   </dependency>
</dependencies>


import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import org.junit.jupiter.api.Test;
import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.SortedMap;
import java.util.TreeMap;

public class ConvertJavaMapToJson {

@Test
public void convertMapToJson() {
    SortedMap<String, String> elements = new TreeMap();
    elements.put("Key1", "Value1");
    elements.put("Key2", "Value2");
    elements.put("Key3", "Value3");

    Gson gson = new Gson();
    Type gsonType = new TypeToken<HashMap>(){}.getType();
    String gsonString = gson.toJson(elements,gsonType);
    System.out.println(gsonString);
}
}

For org.json

<dependencies>
    <dependency>
        <groupId>org.json</groupId>
        <artifactId>json</artifactId>
        <version>20180813</version>
    </dependency>
</dependencies>


import org.json.JSONObject;
import org.junit.jupiter.api.Test;
import java.util.HashMap;
import java.util.Map;

public class ConvertJavaMapToJson {

@Test
public void convertMapToJson() {
    Map<String, String> elements = new HashMap<>();
    elements.put("Key1", "Value1");
    elements.put("Key2", "Value2");
    elements.put("Key3", "Value3");

    JSONObject json = new JSONObject(elements);

    System.out.println(json);
}
}

Convert Map to JSON in Java

2 Answers2