Introduction

Now that you understand the Spring Boot structure and key annotations, it’s time to build your first real CRUD API.
In this lesson, you will create a simple Users API that allows you to:

• Create a user
• Get all users
• Get user by ID
• Update user
• Delete user

We will use:

• Spring Boot
• JPA (Hibernate)
• H2 in-memory database

No external database needed.

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1. Create a New Spring Boot Project

You can generate the project from Spring Initializr with the following dependencies:

• Spring Web
• Spring Data JPA
• H2 Database

Package structure we will use:

com.example.demo
 ├── controller
 ├── service
 ├── repository
 └── model

---

2. Configure H2 In-Memory Database

Add the following to application.properties:

spring.datasource.url=jdbc:h2:mem:testdb
spring.h2.console.enabled=true
spring.jpa.hibernate.ddl-auto=update

Visit the H2 console after running the app:

http://localhost:8080/h2-console

---

3. Create the User Entity

model/User.java

package com.example.demo.model;

import jakarta.persistence.*;

@Entity
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;
    private String email;

    public User() {}

    public User(String name, String email) {
        this.name = name;
        this.email = email;
    }

    // Getters and setters
}

---

4. Create the Repository

repository/UserRepository.java

package com.example.demo.repository;

import com.example.demo.model.User;
import org.springframework.data.jpa.repository.JpaRepository;

public interface UserRepository extends JpaRepository<User, Long> {

}

This provides built-in CRUD operations.

---

5. Create the Service Layer

service/UserService.java

package com.example.demo.service;

import com.example.demo.model.User;
import com.example.demo.repository.UserRepository;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class UserService {

    private final UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public User create(User user) {
        return userRepository.save(user);
    }

    public List<User> findAll() {
        return userRepository.findAll();
    }

    public User findById(Long id) {
        return userRepository.findById(id).orElse(null);
    }

    public User update(Long id, User newUser) {
        User existing = findById(id);
        if (existing == null) return null;

        existing.setName(newUser.getName());
        existing.setEmail(newUser.getEmail());
        return userRepository.save(existing);
    }

    public void delete(Long id) {
        userRepository.deleteById(id);
    }
}

---

6. Create the Controller

controller/UserController.java

package com.example.demo.controller;

import com.example.demo.model.User;
import com.example.demo.service.UserService;
import org.springframework.web.bind.annotation.*;

import java.util.List;

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

    private final UserService userService;

    public UserController(UserService userService) {
        this.userService = userService;
    }

    @PostMapping
    public User create(@RequestBody User user) {
        return userService.create(user);
    }

    @GetMapping
    public List<User> getAll() {
        return userService.findAll();
    }

    @GetMapping("/{id}")
    public User getById(@PathVariable Long id) {
        return userService.findById(id);
    }

    @PutMapping("/{id}")
    public User update(@PathVariable Long id, @RequestBody User user) {
        return userService.update(id, user);
    }

    @DeleteMapping("/{id}")
    public void delete(@PathVariable Long id) {
        userService.delete(id);
    }
}

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7. Test Your API

Run the project, then use Postman or any REST client.

Create User

POST
http://localhost:8080/users
Body:

{
  "name": "John Doe",
  "email": "john@example.com"
}

Get All

GET
http://localhost:8080/users

Get By ID

GET
http://localhost:8080/users/1

Update

PUT
http://localhost:8080/users/1

Delete

DELETE
http://localhost:8080/users/1

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Summary

In this tutorial, you learned how to:

• Configure H2 in-memory database
• Create JPA entity
• Build repository, service, and controller layers
• Test CRUD endpoints

This is your first complete REST API in Spring Boot.