1 import com.fasterxml.jackson.annotation.JsonAutoDetect; import com.fasterxml.jackson.databind.ObjectMapper; import java.io.File; import java.io.IOException; import java.util.ArrayList; import java.util.List; import java.util.Map; public class App { public static void main(String[] args) throws IOException { String fileName = "test.json"; List<Person> people = new ArrayList<>(); Person person = new Person("Ivan", 20, Map.of("tel","25-12-86","mail","1@mail.ru")); people.add(person); person = new Person("Petr", 25, Map.of("tel","35-32-16","mail","2@mail.ru")); people.add(person); ObjectMapper mapper = new ObjectMapper(); mapper.writeValue(new File(fileName), people); } } @JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY) class Person { String name; int age; Map<String, String> contacts; public Person(String name, int age, Map<String, String> contacts) { this.name = name; this.age = age; this.contacts = contacts; } }