Convert JSON String to Map and Map to JSON String with Jackson

In this section, we will show you how to convert JSON String to Map and Map to JSON String with Jackson.

Note

Jackson is a very popular and efficient java based library to serialize or map java objects to JSON and vice versa.

Note

JSON (JavaScript Object Notation) is a lightweight format that is used for data interchanging.

JSON is built on two structures: 

• A collection of name/value pairs. In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array. 
• An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence.

1. Download Jackson

<dependency>
   <groupId>com.fasterxml.jackson.core</groupId>
   <artifactId>jackson-databind</artifactId>
   <version>2.14.1</version>
</dependency>

In Jackson, we can use mapper.readValue(json, Map.class) to convert a JSON string to a Map.

2. JSON string to Map

Main.java

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.IOException;
import java.util.Map;

public class Main {
    public static void main(String[] args) {

        ObjectMapper mapper = new ObjectMapper();
        String json = "{\"name\":\"sibin\", " +
                        "\"email\":\"sibin@gmail.in\"}";

        try {

            // convert JSON string to Map
            Map<String, String> map1 = mapper
                    .readValue(json, Map.class);

            
            Map<String, String> map2 = mapper.readValue(json,
                    new TypeReference<Map<String, String>>() {});

            System.out.println(map1);
            System.out.println(map2);

        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

Console Output:

{name=sibin, email=sibin@gmail.in}
{name=sibin, email=sibin@gmail.in}

3. Map to JSON string

Main.java

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.HashMap;
import java.util.Map;

public class Main {

    public static void main(String[] args) {

        ObjectMapper mapper = new ObjectMapper();

        Map<String, String> map = new HashMap<>();
        map.put("name", "sibin");
        map.put("email", "sibin@gmail.in");

        try {

            // convert map to JSON string
            String json1 = mapper.writeValueAsString(map);

            System.out.println(json1);   // compact-print

            // convert map to JSON string - pretty print
            String json2 = mapper.writerWithDefaultPrettyPrinter()
                    .writeValueAsString(map);

            System.out.println(json2);

        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
    }
}

Console Output:

{"name":"sibin","email":"sibin@gmail.in"}
{
  "name" : "sibin",
  "email" : "sibin@gmail.in"
}

More related topics,

• Moshi - Convert JSON Array String to List and List to JSON Array String

• Moshi - How to convert Java object to JSON and JSON to Java object

• Genson - Convert JSON Array String to List and List to JSON Array String

• Genson - How to convert Java object to JSON and JSON to Java object

• Convert JSON Array String to List and List to JSON Array String with Jackson

• Convert JSON String to Map and Map to JSON String with Jackson

• How to convert Java object to JSON and JSON to Java object with Gson?