Convert List of POJO to JSON in Java

We can use the Jackson and Gson libraries to convert in Java to a List of POJOs to JSON. This topic explains step-by-step how to convert a List of POJOs to JSON in Java using these libraries. 

Ways to Convert List of POJO to JSON

These are the following ways to convert list of POJO to JSON:

• Using Jackson Library
• Using Gson Library

Using Jackson

1. Add Dependency (Maven)

<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.15.0</version> <!-- Use latest version -->
</dependency>

2. Create a POJO

class User {

    private String name;

    private int age;

    // Constructors, getters, setters

    public User() {}

    public User(String name, int age) {

        this.name = name;

        this.age = age;

    }

    // Getters and Setters (Required for Jackson)

    public String getName() { return name; }

    public void setName(String name) { this.name = name; }

    public int getAge() { return age; }

    public void setAge(int age) { this.age = age; }

}

3. Sample Code

import com.fasterxml.jackson.databind.ObjectMapper;

import java.util.List;

import java.util.ArrayList;

public class Main {

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

        List<User> users = new ArrayList<>();

        users.add(new User("John", 25));

        users.add(new User("Alice", 30));

        ObjectMapper mapper = new ObjectMapper();

        String json = mapper.writeValueAsString(users);

        System.out.println(json);

    }

}

Output:

[{"name":"John","age":25},{"name":"Alice","age":30}]

Using Gson

1. Add Dependency (Maven)

<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.10</version> <!-- Use latest version -->
</dependency>

2. Create a POJO class

class User {

    private String name;

    private int age;

    public User(String name, int age) {

        this.name = name;

        this.age = age;

    }

}

3. Sample Code

import com.google.gson.Gson;

import java.util.List;

import java.util.ArrayList;

public class Main {

    public static void main(String[] args) {

        List<User> users = new ArrayList<>();

        users.add(new User("John", 25));

        users.add(new User("Alice", 30));

        Gson gson = new Gson();

        String json = gson.toJson(users);

        System.out.println(json);

    }

}

Output:

[{"name":"John","age":25},{"name":"Alice","age":30}]

Convert List of POJOs to JSON

Library	Dependency	Method
Jackson	jackson-databind	ObjectMapper().writeValueAsString()
Gson	gson	Gson().toJson()

• Both are great options. Jackson is slightly more powerful and commonly used with Spring Boot.

Conclusion

In this topic, we learnt about how to convert a list of POJOs to JSON in Java using Jackson and Gson libraries in Java.