Gson gson= new Gson(); CustomPOJOClass obj = gson.fromJson(jsonObject.toString(),CustomPOJOClass.class);User u = new User(); u.firstName = "Sample"; u.lastName = "User"; u.email = "sampleU@example.com"; ObjectMapper mapper = new ObjectMapper(); try { // convert user object to json string and return it return mapper.writeValueAsString(u); } catch (JsonGenerationException | JsonMappingException e) { // catch various errors e.printStackTrace(); }public class Student { Integer id; Map<String,Integer> marks; List<Address> addresses; public Student(Integer id, Map<String, Integer> marks, List<Address> addresses) { this.id = id; this.marks = marks; this.addresses = addresses; } } class Address { String addrType; Integer houseNo; String streetName; String countryName; House house; public Address(String addrType, Integer houseNo, String streetName, String countryName, House house) { this.addrType = addrType; this.houseNo = houseNo; this.streetName = streetName; this.countryName = countryName; this.house = house; } } class House { Integer noOfRooms; String houseType; Integer noOfWindows; public House(Integer noOfRooms, String houseType, Integer noOfWindows) { this.noOfRooms = noOfRooms; this.houseType = houseType; this.noOfWindows = noOfWindows; } }system.out.println("Miladheydarloo");