Serialize /Convert Map of object to/from JSON in java (GSON /example)

Given the Map of String and object (Map<String,Object>), we would like to convert Map to JSON and vice versa.
We will use the Google gson library to achieve serialization and deserialization process.
We will create Person class and we will perform the following operations with Person class
1. Convert Map<String,Person> to JSON string
2. Convert the JSON string to Map<String,Person>

GSON Maven dependency:

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.5</version>
</dependency>

Program – convert Map <k,v> to/from JSON in java(GSON /example)

1.) Person Class:

Person class containing firstName, lastName, age etc.
We have overloaded toString method to print person information.

package org.learn.gson;
 
public class Person {
    public String firstName;
    public String lastName;
    public int age;
    public String contact;
 
    public Person(String firstName, String lastName, int age, String contact) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
        this.contact = contact;
    }
 
    public String toString() {
        return "[" + firstName + " " + lastName + " " + age + " " + contact + "]";
    }
}

2.) JSONMapConverter Class:

JSONMapConverter is responsible for performing following operations.

Convert Map<String,Person> to JSON string in java.
Convert the JSON string to Map<String,Person> in java.

package org.learn.gson;
 
import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.Map;
 
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.reflect.TypeToken;
 
public class JSONMapConverter {
    public static void main(String[] args) {
        Gson objGson = new GsonBuilder().setPrettyPrinting().create();
 
        Map<String, Person> mapIdPerson = new HashMap<>();
        mapIdPerson.put("10101001", new Person("Mike", "harvey", 34, "001894536"));
        mapIdPerson.put("20202002", new Person("Nick", "young", 75, "005425676"));
        mapIdPerson.put("30303003", new Person("gary", "hudson", 21, "009654153"));
        mapIdPerson.put("40404004", new Person("gary", "hudson", 55, "00564536"));
 
        Type listType = new TypeToken<Map<String, Person>>() {
        }.getType();
        String mapToJson = objGson.toJson(mapIdPerson);
        System.out.println("1. Map to JSON conversion is : \n");
        System.out.println(mapToJson);
 
        // JSON to Map
        Map<String, Person> jsonToMap = objGson.fromJson(mapToJson, listType);
        System.out.println("2. JSON to Map conversion is :\n");
        jsonToMap.forEach((k, v) -> System.out.println(k + "=" + v));
    }
}

Download Code – Convert Map to JSON Java (GSON /Example)

Output – convert Map <k,v> to/from JSON in java (GSON /example)

1. <strong>Map to JSON conversion is</strong> :
 
{
"30303003": {
"firstName": "gary",
"lastName": "hudson",
"age": 21,
"contact": "009654153"
},
"10101001": {
"firstName": "Mike",
"lastName": "harvey",
"age": 34,
"contact": "001894536"
},
"20202002": {
"firstName": "Nick",
"lastName": "young",
"age": 75,
"contact": "005425676"
},
"40404004": {
"firstName": "gary",
"lastName": "hudson",
"age": 55,
"contact": "00564536"
}
}
2. <strong>JSON to Map conversion is </strong>:
 
30303003=[gary hudson 21 009654153]
10101001=[Mike harvey 34 001894536]
20202002=[Nick young 75 005425676]
40404004=[gary hudson 55 00564536]

GSON Maven dependency:

Program – convert Map <k,v> to/from JSON in java(GSON /example)

1.) Person Class:

2.) JSONMapConverter Class:

Output – convert Map <k,v> to/from JSON in java (GSON /example)

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