Building a Complete CRUD API with Spring Boot and H2 Database

Building a CRUD (Create, Read, Update, Delete) API is one of the foundational skills every backend developer should master. In this tutorial, we’ll walk through building a full-fledged CRUD REST API using Spring Boot and the in-memory H2 database.

This project is perfect for beginners who want to practice backend development without setting up an external database.

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✅ What You’ll Build

We’ll create a simple Employee Management API with the following endpoints:

• POST /employees – Create a new employee

• GET /employees – Get all employees

• GET /employees/{id} – Get a single employee by ID

• PUT /employees/{id} – Update employee info

• DELETE /employees/{id} – Delete employee

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🛠️ Technologies Used

• Java 17+

• Spring Boot 3.x

• Spring Web

• Spring Data JPA

• H2 Database

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📦 Step 1: Set Up the Project

Visit https://start.spring.io and generate a new Maven project with:

• Dependencies:

  • Spring Web

  • Spring Data JPA

  • H2 Database

Group: com.example
Artifact: crudapi

Extract and open the project in your IDE (e.g., IntelliJ or Eclipse).

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📁 Step 2: Define the Entity

Create an Employee entity in com.example.crudapi.model:

package com.example.crudapi.model;

import jakarta.persistence.*;

@Entity
public class Employee {

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

    private String name;
    private String role;

    // Constructors
    public Employee() {}

    public Employee(String name, String role) {
        this.name = name;
        this.role = role;
    }

    // Getters & Setters
    public Long getId() { return id; }
    public String getName() { return name; }
    public String getRole() { return role; }

    public void setId(Long id) { this.id = id; }
    public void setName(String name) { this.name = name; }
    public void setRole(String role) { this.role = role; }
}

🧩 Step 3: Create the Repository

Create a simple JPA repository in com.example.crudapi.repository:

package com.example.crudapi.repository;

import com.example.crudapi.model.Employee;
import org.springframework.data.jpa.repository.JpaRepository;

public interface EmployeeRepository extends JpaRepository<Employee, Long> {}

🎯 Step 4: Build the Service Layer (Optional but Recommended)

package com.example.crudapi.service;

import com.example.crudapi.model.Employee;
import com.example.crudapi.repository.EmployeeRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;
import java.util.Optional;

@Service
public class EmployeeService {

    @Autowired
    private EmployeeRepository repository;

    public List<Employee> getAll() {
        return repository.findAll();
    }

    public Optional<Employee> getById(Long id) {
        return repository.findById(id);
    }

    public Employee create(Employee employee) {
        return repository.save(employee);
    }

    public Employee update(Long id, Employee updated) {
        return repository.findById(id)
            .map(e -> {
                e.setName(updated.getName());
                e.setRole(updated.getRole());
                return repository.save(e);
            })
            .orElseThrow(() -> new RuntimeException("Employee not found"));
    }

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

🌐 Step 5: Create the Controller

package com.example.crudapi.controller;

import com.example.crudapi.model.Employee;
import com.example.crudapi.service.EmployeeService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@RestController
@RequestMapping("/employees")
public class EmployeeController {

    @Autowired
    private EmployeeService service;

    @GetMapping
    public List<Employee> getAll() {
        return service.getAll();
    }

    @GetMapping("/{id}")
    public Employee getById(@PathVariable Long id) {
        return service.getById(id)
            .orElseThrow(() -> new RuntimeException("Employee not found"));
    }

    @PostMapping
    public Employee create(@RequestBody Employee employee) {
        return service.create(employee);
    }

    @PutMapping("/{id}")
    public Employee update(@PathVariable Long id, @RequestBody Employee employee) {
        return service.update(id, employee);
    }

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

⚙️ Step 6: Configure H2 Database

In src/main/resources/application.properties:

# H2 DB Settings
spring.datasource.url=jdbc:h2:mem:testdb
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
spring.h2.console.enabled=true
spring.jpa.show-sql=true
spring.jpa.hibernate.ddl-auto=update

Access H2 Console at:
➡️ http://localhost:8080/h2-console
Use jdbc:h2:mem:testdb as JDBC URL.

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🚀 Step 7: Run and Test

Run the CrudapiApplication.java main class.

Use Postman or cURL to test the API:

• Create:
  POST /employees with body:

    { "name": "Alice", "role": "Engineer" }
  

• Read all:
  GET /employees

• Read by ID:
  GET /employees/1

• Update:
  PUT /employees/1 with body:

    { "name": "Alice Smith", "role": "Senior Engineer" }
  

• Delete:
  DELETE /employees/1

✅ Summary

You’ve successfully created a complete CRUD REST API using:

• Spring Boot for the framework

• Spring Data JPA for persistence

• H2 for a lightweight, in-memory database

This is a perfect foundation for building more complex APIs. You can now connect to MySQL/PostgreSQL, add validations, implement DTOs, or secure your API with Spring Security.