Spring Boot DTO Example Tutorial

In the previous tutorialwe created a Spring boot project and build CRUD RESTful Webservices using Spring Boot 3, Spring Data JPA (Hibernate), and MySQL database.

In this tutorial, we will see how to DTO (Data Transfer Object) pattern to transfer the data between the Client and Server in the Spring boot application.

DTO ( Data Transfer Object) Overview

Data Transfer Object Design Pattern is a frequently used design pattern. It is basically used to pass data with multiple attributes in one shot from client to server, to avoid multiple calls to a remote server.

Another advantage of using DTOs on RESTful APIs written in Java (and on Spring Boot), is that they can help to hide implementation details of domain objects (JPA entities). Exposing entities through endpoints can become a security issue if we do not carefully handle what properties can be changed through what operations.

Prerequisites

This tutorial is a continuation of Spring Boot 3 CRUD RESTful WebServices with MySQL Database tutorial so first, you need to create a Spring Boot project with CRUD REST API's using this tutorial:

Spring Boot 3 CRUD RESTful WebServices with MySQL Database 

Development Steps

1. Create UserDto Class
2. Change CRUD REST API's to Return UserDTO to the Client
3. Create UserMapper class
4. Change Service Layer to use UserDto
5. Test CRUD REST API's using Postman Client

1. Create UserDto Class

package net.javaguides.springboot.dto;

import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;

@Setter
@Getter
@NoArgsConstructor
@AllArgsConstructor
public class UserDto {
    private Long id;
    private String firstName;
    private String lastName;
    private String email;
}

2. Change CRUD REST API's to Return UserDTO to the Client

package net.javaguides.springboot.controller;

import lombok.AllArgsConstructor;
import net.javaguides.springboot.dto.UserDto;
import net.javaguides.springboot.entity.User;
import net.javaguides.springboot.exception.ErrorDetails;
import net.javaguides.springboot.exception.ResourceNotFoundException;
import net.javaguides.springboot.service.UserService;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.context.request.WebRequest;

import java.time.LocalDateTime;
import java.util.List;

@RestController
@AllArgsConstructor
@RequestMapping("api/users")
public class UserController {

    private UserService userService;

    // build create User REST API
    @PostMapping
    public ResponseEntity<UserDto> createUser(@RequestBody UserDto user){
        UserDto savedUser = userService.createUser(user);
        return new ResponseEntity<>(savedUser, HttpStatus.CREATED);
    }

    // build get user by id REST API
    // http://localhost:8080/api/users/1
    @GetMapping("{id}")
    public ResponseEntity<UserDto> getUserById(@PathVariable("id") Long userId){
        UserDto user = userService.getUserById(userId);
        return new ResponseEntity<>(user, HttpStatus.OK);
    }

    // Build Get All Users REST API
    // http://localhost:8080/api/users
    @GetMapping
    public ResponseEntity<List<UserDto>> getAllUsers(){
        List<UserDto> users = userService.getAllUsers();
        return new ResponseEntity<>(users, HttpStatus.OK);
    }

    // Build Update User REST API
    @PutMapping("{id}")
    // http://localhost:8080/api/users/1
    public ResponseEntity<UserDto> updateUser(@PathVariable("id") Long userId,
                                           @RequestBody UserDto user){
        user.setId(userId);
        UserDto updatedUser = userService.updateUser(user);
        return new ResponseEntity<>(updatedUser, HttpStatus.OK);
    }

    // Build Delete User REST API
    @DeleteMapping("{id}")
    public ResponseEntity<String> deleteUser(@PathVariable("id") Long userId){
        userService.deleteUser(userId);
        return new ResponseEntity<>("User successfully deleted!", HttpStatus.OK);
    }
}

3. Create UserMapper Class

Let's create a UserMapper class to convert the User entity to UserDto and UserDto to the User entity:
package net.javaguides.springboot.mapper;

import net.javaguides.springboot.dto.UserDto;
import net.javaguides.springboot.entity.User;

public class UserMapper {

    // Convert User JPA Entity into UserDto
    public static UserDto mapToUserDto(User user){
        UserDto userDto = new UserDto(
                user.getId(),
                user.getFirstName(),
                user.getLastName(),
                user.getEmail()
        );
        return userDto;
    }

    // Convert UserDto into User JPA Entity
    public static User mapToUser(UserDto userDto){
        User user = new User(
                userDto.getId(),
                userDto.getFirstName(),
                userDto.getLastName(),
                userDto.getEmail()
        );
        return user;
    }
}

4. Change Service Layer to use UserDto

Change UserService Interface

package net.javaguides.springboot.service;

import net.javaguides.springboot.dto.UserDto;
import net.javaguides.springboot.entity.User;

import java.util.List;

public interface UserService {
    UserDto createUser(UserDto user);

    UserDto getUserById(Long userId);

    List<UserDto> getAllUsers();

    UserDto updateUser(UserDto user);

    void deleteUser(Long userId);
}

Change UserServiceImpl class

package net.javaguides.springboot.service.impl;

import lombok.AllArgsConstructor;
import net.javaguides.springboot.dto.UserDto;
import net.javaguides.springboot.entity.User;
import net.javaguides.springboot.mapper.UserMapper;
import net.javaguides.springboot.repository.UserRepository;
import net.javaguides.springboot.service.UserService;
import org.apache.logging.log4j.util.Strings;
import org.springframework.stereotype.Service;
import org.springframework.util.StringUtils;

import java.util.List;
import java.util.Objects;
import java.util.Optional;
import java.util.stream.Collectors;

@Service
@AllArgsConstructor
public class UserServiceImpl implements UserService {

    private UserRepository userRepository;

    @Override
    public UserDto createUser(UserDto userDto) {

        // Convert UserDto into User JPA Entity
        User user = UserMapper.mapToUser(userDto);

        User savedUser = userRepository.save(user);

        // Convert User JPA entity to UserDto
        UserDto savedUserDto = UserMapper.mapToUserDto(savedUser);

        return savedUserDto;
    }

    @Override
    public UserDto getUserById(Long userId) {
        Optional<User> optionalUser = userRepository.findById(userId);
        User user = optionalUser.get();
        return UserMapper.mapToUserDto(user);
    }

    @Override
    public List<UserDto> getAllUsers() {
        List<User> users = userRepository.findAll();
        return users.stream().map(UserMapper::mapToUserDto)
                .collect(Collectors.toList());
    }

    @Override
    public UserDto updateUser(UserDto user) {
        User existingUser = userRepository.findById(user.getId()).get();
        existingUser.setFirstName(user.getFirstName());
        existingUser.setLastName(user.getLastName());
        existingUser.setEmail(user.getEmail());
        User updatedUser = userRepository.save(existingUser);
        return UserMapper.mapToUserDto(updatedUser);
    }

    @Override
    public void deleteUser(Long userId) {
        userRepository.deleteById(userId);
    }
}

5. Test CRUD REST API's using Postman Client

Create User REST API:

HTTP Method: POST
Request Body:
{
    "firstName": "ramesh",
    "lastName":"fadatare",
    "email": "ramesh@gmail.com"
}
Refer to this screenshot to test Create User REST API:

Get User REST API:

HTTP Method: GET

Refer to this screenshot to test GET User REST API:

Update User REST API:

HTTP Method: PUT
Request Body:
{
    "firstName": "ram",
    "lastName":"fadatare",
    "email": "ram@gmail.com"
}
Refer to this screenshot to test the Update User REST API:

Get All Users REST API:

HTTP Method: GET

Refer to this screenshot to test GET All User REST API:

DELETE User REST API:

HTTP Method: DELETE

Refer to this screenshot to test Delete User REST API:

Source Code on GitHub

The source code of this tutorial is available on my GitHub repository at Spring Boot CRUD RESTful WebServices

Conclusion

In this tutorial, we have seen how to use DTO (Data Transfer Object) pattern to transfer the database between the client and server in the Spring boot application.

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