Convert Map to/from JSON string in java (jackson objectmapper/ example)

• Given Map of String & object (Map<String,Object>), we would like to convert Map to/from JSON.
• We will use the jackson’s objectmapper to serialize Map to JSON &  deserialize JSON to Map.
• We will create Person class &  we will perform following operations with Person class.
  1. Convert Map<String,Person> to JSON String in java
  2. Convert JSON String to Map<String,Person> in java

Jackson objectMapper maven Dependencies

<dependency>
 <groupId>com.fasterxml.jackson.core</groupId> 
 <artifactId>jackson-databind</artifactId>
 <version>2.7.1</version> 
</dependency>

Serialize or Convert Map to/from JSON in java (jackson objectmapper)

1.) Person Class:

• Person class containing attributes of Person.

package org.learn;

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

2.) JSONMapConverter Class:

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

package org.learn;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

public class JSONMapConverter 
{
    public static void main( String[] args ) throws IOException
    {
     ObjectMapper objectMapper = new ObjectMapper();
     //Set pretty printing of json
     objectMapper.enable(SerializationFeature.INDENT_OUTPUT);

     //Define map which will be converted to JSON
     Map<String,Person>mapIdPerson  = new HashMap<>();
     mapIdPerson.put("10101001", new Person("Mike", "harvey", 34));
     mapIdPerson.put("20202002", new Person("Nick", "young", 75));
     mapIdPerson.put("30303003", new Person("gary", "hudson", 21));
     mapIdPerson.put("40404004", new Person("gary", "hudson", 55));
     
     //1. Convert Map to JSON
     String mapToJson = objectMapper.writeValueAsString(mapIdPerson);
     System.out.println("1. Convert Map to JSON :");
     System.out.println(mapToJson);
     
     //2. JSON to Map
     //Define Custom Type reference for map type
     TypeReference<Map<String, Person>> mapType = new TypeReference<Map<String,Person>>() {};
     Map<String,Person> jsonToMap = objectMapper.readValue(mapToJson, mapType);
     System.out.println("\n2. Convert JSON to Map :");
     
     //Print map output using Java 8
     jsonToMap.forEach((k, v) -> 
          System.out.println(k + "=" + v));
    }
}

Download Example Code – Convert Serialize Jackson Map to JSON Java

Output – Serialize/convert Map to/from JSON in java (jackson objectmapper)

1. Convert Map to JSON :
{
  "30303003" : {
    "firstName" : "gary",
    "lastName" : "hudson",
    "age" : 21
  },
  "10101001" : {
    "firstName" : "Mike",
    "lastName" : "harvey",
    "age" : 34
  },
  "20202002" : {
    "firstName" : "Nick",
    "lastName" : "young",
    "age" : 75
  },
  "40404004" : {
    "firstName" : "gary",
    "lastName" : "hudson",
    "age" : 55
  }
}

2. Convert JSON to Map :
30303003=[gary hudson 21]
10101001=[Mike harvey 34]
20202002=[Nick young 75]
40404004=[gary hudson 55]