How do I convert collections into JSON?

This example show you how to convert Java collections object into JSON string. For Student class use in this example you can find it the previous example on How do I convert object into JSON?.

package org.kodejava.gson;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import org.kodejava.gson.support.Student;

import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.List;

public class CollectionToJson {
    public static void main(String[] args) {
        // Converts a collection of string object into JSON string.
        List<String> names = new ArrayList<>();
        names.add("Alice");
        names.add("Bob");
        names.add("Carol");
        names.add("Mallory");

        Gson gson = new Gson();
        String jsonNames = gson.toJson(names);
        System.out.println("jsonNames = " + jsonNames);

        // Converts a collection Student object into JSON string
        Student a = new Student("Alice", "Apple St", getDOB(2000, 10, 1));
        Student b = new Student("Bob", "Banana St", null);
        Student c = new Student("Carol", "Grape St", getDOB(2000, 5, 21));
        Student d = new Student("Mallory", "Mango St", null);

        List<Student> students = new ArrayList<>();
        students.add(a);
        students.add(b);
        students.add(c);
        students.add(d);

        gson = new Gson();
        String jsonStudents = gson.toJson(students);
        System.out.println("jsonStudents = " + jsonStudents);

        // Converts JSON string into a collection of Student object.
        Type type = new TypeToken<List<Student>>() {
        }.getType();
        List<Student> studentList = gson.fromJson(jsonStudents, type);

        for (Student student : studentList) {
            System.out.println("student.getName() = " + student.getName());
        }
    }

    private static Date getDOB(int year, int month, int date) {
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.YEAR, year);
        calendar.set(Calendar.MONTH, month - 1);
        calendar.set(Calendar.DATE, date);
        calendar.set(Calendar.HOUR, 0);
        calendar.set(Calendar.MINUTE, 0);
        calendar.set(Calendar.SECOND, 0);
        return calendar.getTime();
    }
}

Here is the result of our program:

jsonNames = ["Alice","Bob","Carol","Mallory"]
jsonStudents = [{"name":"Alice","address":"Apple St","dateOfBirth":"Oct 1, 2000, 12:00:00 AM"},{"name":"Bob","address":"Banana St"},{"name":"Carol","address":"Grape St","dateOfBirth":"May 21, 2000, 12:00:00 AM"},{"name":"Mallory","address":"Mango St"}]
student.getName() = Alice
student.getName() = Bob
student.getName() = Carol
student.getName() = Mallory

Maven Dependencies

<!--http://repo1.maven.org/maven2/com/google/code/gson/gson/2.8.8/gson-2.8.8.jar-->
<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.8</version>
</dependency>

Author
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Wayan

Founder at Kode Java Org

I am a programmer, a runner, a recreational diver, currently live in the island of Bali, Indonesia. Mostly programming in Java, Spring Framework, Hibernate / JPA. If these posts help, you can support me, buy me a cup of coffee or tea. Thank you 🥳

How do I convert collections into JSON?

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