Jackson - Convert Map to JSON Object

In this quick article, I will show how to convert a Map to a JSON object using the Jackson library.

Check out complete Jackson tutorial at Java Jackson JSON Tutorial with Examples.

We are using Jackson library to convert Java Map to JSON array so let's add below Jackson dependency to your project's classpath or pom.xml.

Maven pom dependency

Let’s first add the following dependencies to the pom.xml:

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

This dependency will also transitively add the following libraries to the classpath:

• jackson-annotations-2.9.8.jar
• jackson-core-2.9.8.jar
• jackson-databind-2.9.8.jar

Always use the latest versions on the Maven central repository for Jackson databind.

Example - Convert Map to JSON Object

The following example shows how to convert Map to JSON object using the ObjectMapper.writeValueAsString() method.

JacksonMapToJson.java

package net.javaguides.jackson;

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

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

public class JacksonMapToJson {

    public static void main(String[] args) throws JsonProcessingException {

        ObjectMapper mapper = new ObjectMapper();
        mapper.enable(SerializationFeature.INDENT_OUTPUT);

        Map < String, Integer > days = new HashMap < > ();
        days.put("MON", Calendar.MONDAY);
        days.put("TUE", Calendar.TUESDAY);
        days.put("WED", Calendar.WEDNESDAY);
        days.put("THU", Calendar.THURSDAY);
        days.put("FRI", Calendar.FRIDAY);
        days.put("SAT", Calendar.SATURDAY);
        days.put("SUN", Calendar.SUNDAY);

        String json = mapper.writeValueAsString(days);
        System.out.println(json);
    }
}

Output:

{
  "THU" : 5,
  "TUE" : 3,
  "WED" : 4,
  "SAT" : 7,
  "FRI" : 6,
  "MON" : 2,
  "SUN" : 1
}

Related Jackson JSON Examples

• Jackson - Convert Java Object to/from JSON Example  (popular)

• Jackson - List, Set, and Map Serialization and Deserialization in Java Examples

• Change Field Name in JSON using Jackson  (popular)

• How to Read / Write JSON Using Jackson JsonParser and JsonGenerator

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• Jackson @JsonPropertyOrder Example

• Jackson - Ignore Fields or Properties on Serialization

• Jackson @JsonIgnore, @JsonIgnoreProperties and @JsonIgnoreType  (popular)

• Jackson Ignore Null and Empty Fields on Serialization  (popular)

• Jackson @JsonInclude Example

• ObjectMapper - Java to JSON

• ObjectMapper - JSON to Java Object

• Convert List to JSON Array Using Jackson

• Convert Set to JSON Array Using Jackson