Jackson – Convert JSON string to Map – Mkyong.com

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

P.S Tested with Jackson 2.9.8

pom.xml

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

1. JSON string to Map

JacksonMapExample1.java

package com.mkyong;

import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;
import java.util.Map;

public class JacksonMapExample1 {

    public static void main(String[] args) {

        ObjectMapper mapper = new ObjectMapper();
        String json = "{\"name\":\"mkyong\", \"age\":\"37\"}";

        try {

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

            // it works
            //Map<String, String> map = mapper.readValue(json, new TypeReference<Map<String, String>>() {});

            System.out.println(map);

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

    }
}

Output

{name=mkyong, age=37}

2. Map to JSON string

JacksonMapExample2.java

package com.mkyong;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.util.HashMap;
import java.util.Map;

public class JacksonMapExample2 {

    public static void main(String[] args) {

        ObjectMapper mapper = new ObjectMapper();

        Map<String, String> map = new HashMap<>();
        map.put("name", "mkyong");
        map.put("age", "37");

        try {

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

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

            json = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(map);

            System.out.println(json);   // pretty-print

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


    }
}

Output

{"name":"mkyong","age":"37"}
{
  "name" : "mkyong",
  "age" : "37"
}

3. JSON Array to Map?

3.1 JSON array string like this

[{"age":29,"name":"mkyong"}, {"age":30,"name":"fong"}]

It should convert to a List, instead of a Map, for example :

    // convert JSON array to List
    List<Person> list = Arrays.asList(mapper.readValue(json, Person[].class));

Note
Read this Jackson – Convert JSON array string to List

References

jackson json map

Original url: Access
Created at: 2019-12-10 19:50:07
Category: default
Tags: none

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