How to Convert a HashSet to JSON in Java?

In Java, a HashSet is an implementation of the Set interface that uses a hash table to store elements. It allows fast lookups and does not allow duplicate elements. Elements in a HashSet are unordered and can be of any object type. In this article, we will see how to convert a HashSet to JSON in Java.

Steps to convert a HashSet to JSON in Java

Below are the steps and implementation of converting a HashSet to JSON in Java with Jackson.

Step 1: Create a Maven Project

Open any preferred IDE and Create a new Maven project. Here, we are using IntelliJ IDEA. So, we can do this by selecting File -> New -> Project.. -> Maven and following the wizard.

Project Structure:

Below is the project structure that we have created.

Step 2: Add Jackson Dependency to the pom.xml

Now, we will add Jackson dependency to pom.xml file.

XML

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>HashSet</artifactId>
    <version>1.0-SNAPSHOT</version>
    <dependencies>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.13.0</version>
        </dependency>
    </dependencies>
    <properties>
        <maven.compiler.source>21</maven.compiler.source>
        <maven.compiler.target>21</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

</project>

Step 3: Add logic of Conversion of a HashSet to JSON String

Below is the implementation to convert a HashSet to JSON with Jackson.

Java

// Java Program for Conversion of a HashSet to JSON String
package org.example;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectWriter;
import java.util.HashSet;

// Main Class
public class Main {
      // main function
    public static void main(String[] args)
    {
        // Create a HashSet of courses
        HashSet<String> courses = new HashSet<>();
        courses.add("Java");
        courses.add("Python");
        courses.add("C++");

        // Create ObjectMapper
        ObjectMapper mapper = new ObjectMapper();

        try {
            // Create ObjectWriter with default pretty printer
            ObjectWriter writer = mapper.writerWithDefaultPrettyPrinter();

            // Convert HashSet to JSON
            String jsonData = writer.writeValueAsString(courses);

            // Print JSON Data
            System.out.println(jsonData);
        }
        catch (JsonProcessingException e) {
            e.printStackTrace();
        }
    }
}

Explanation of the above code:

• It creates a HashSet of courses – Java, Python, C++
• Jackson ObjectMapper is used to convert Java objects to JSON.
• ObjectWriter is used to format the JSON with proper indentation.
• HashSet is converted to a JSON string using ObjectWriter.
• The JSON string is printed to the output.

Output: