Spring Boot Tutorial

What is Spring Boot?

Spring Boot is a Java-based framework used to build web applications, REST APIs, microservices, and enterprise applications quickly and easily. It is built on top of the Spring Framework and reduces the configuration required to create a Spring application.

Spring Boot follows the principle:

Convention over Configuration

Spring Boot provides sensible default configurations so developers can focus on business logic instead of spending most of their time on application setup.

Why Do We Need Spring Boot?

Before Spring Boot, developers often had to perform many manual steps:

• Configure XML files
• Set up application servers
• Configure dependencies manually
• Configure database connections
• Configure component scanning
• Package and deploy the application separately

Spring Boot simplifies these tasks through automatic configuration and built-in tools.

How Spring Boot Works

Spring Boot checks the dependencies in the project and automatically configures the application.

For example, adding Spring Web configures a web server, Spring MVC, request handling, JSON conversion, and basic error handling.

Spring Boot Application
          ↓
Checks Project Dependencies
          ↓
Applies Auto-Configuration
          ↓
Starts Embedded Server
          ↓
Application is Ready

Key Features of Spring Boot

1. Auto-Configuration

Spring Boot configures the application based on the libraries available in the project. Adding Spring Data JPA automatically prepares many database-related components.

2. Embedded Web Server

Spring Boot includes Tomcat, Jetty, and Undertow. An external application server is not required.

java -jar application.jar

3. Spring Boot Starters

Starter dependencies group commonly used libraries together:

• spring-boot-starter-web
• spring-boot-starter-data-jpa
• spring-boot-starter-security
• spring-boot-starter-test

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

4. Minimal Configuration

Most configuration can be handled using annotations and property files such as application.properties or application.yml.

server.port=8081
spring.application.name=employee-service

5. Production-Ready Features

Spring Boot Actuator helps monitor application health, memory usage, environment properties, metrics, beans, and HTTP requests.

/actuator/health

6. Dependency Management

Spring Boot manages compatible dependency versions automatically, reducing conflicts and simplifying maintenance.

7. Easy REST API Development

REST APIs can be created with annotations such as @RestController, @RequestMapping, @GetMapping, @PostMapping, @PutMapping, and @DeleteMapping.

@RestController
@RequestMapping("/api")
public class WelcomeController {

    @GetMapping("/welcome")
    public String welcome() {
        return "Welcome to Spring Boot!";
    }
}

The endpoint can be accessed at http://localhost:8080/api/welcome.

8. Microservices Support

Each Spring Boot service can run independently with its own business logic, database, server, and deployment process.

Spring Boot integrates with Spring Cloud, Kafka, Docker, Kubernetes, API Gateway, and service discovery.

9. Easy Database Integration

Spring Boot supports MySQL, PostgreSQL, Oracle, MongoDB, and SQL Server through Spring JDBC, Spring Data JPA, Hibernate, and Spring Data MongoDB.

spring.datasource.url=jdbc:mysql://localhost:3306/company_db
spring.datasource.username=root
spring.datasource.password=password

10. Easy Testing

Common testing tools include JUnit, Mockito, MockMvc, and Spring Boot Test.

@SpringBootTest
class ApplicationTests {

    @Test
    void contextLoads() {
    }
}

Common Uses of Spring Boot

REST APIs

Build employee management, payment, order management, and customer APIs.

Web Applications

Spring Boot works with Angular, React, Vue.js, HTML, and Bootstrap.

Microservices

Services can be developed, deployed, and scaled independently.

Enterprise Applications

Spring Boot is widely used in banking, healthcare, insurance, e-commerce, telecommunications, and logistics.

Cloud Applications

Applications can run on AWS, Microsoft Azure, Google Cloud, Docker, and Kubernetes.

Simple Spring Boot Application

@SpringBootApplication
public class SpringBootApplicationExample {

    public static void main(String[] args) {
        SpringApplication.run(
            SpringBootApplicationExample.class,
            args
        );
    }
}

Explanation

• @SpringBootApplication enables auto-configuration, component scanning, and configuration support.
• SpringApplication.run() starts the application and embedded web server.

Simple REST Controller Example

@RestController
public class HelloController {

    @GetMapping("/hello")
    public String sayHello() {
        return "Hello from Spring Boot!";
    }
}

After starting the application, open http://localhost:8080/hello to see Hello from Spring Boot!.

Spring Framework vs Spring Boot

Advantages of Spring Boot

• Faster application development
• Less manual configuration
• Embedded web server
• Easy dependency management
• Easy REST API development
• Microservices support
• Production-ready monitoring
• Easy database integration
• Easy cloud deployment
• Strong Spring ecosystem support

Summary

Spring Boot simplifies Spring application development with auto-configuration, starter dependencies, embedded servers, minimal configuration, REST API support, database integration, testing support, production monitoring, microservices support, and cloud deployment. Developers can focus on business requirements while Spring Boot handles most application setup and configuration.

Spring Boot Core

Understand how a Spring Boot application starts and how its core building blocks work together. This foundation covers auto-configuration, starters, application context, dependency injection, bean lifecycle, configuration properties, and profiles so you can build a maintainable application before adding web or database features.

Aspect-Oriented Programming (AOP)

Learn how AOP keeps cross-cutting behavior such as logging, transactions, security, caching, and performance monitoring separate from business logic. You will understand advice, pointcuts, aspects, custom annotations, and the situations where AOP improves a design.

Spring Data JPA

Learn how Spring Data JPA connects Java domain objects with relational databases through entities, repositories, relationships, queries, and transactions. The topic also explains CRUD workflows, pagination, database configuration, MongoDB integration, auditing, and common performance issues such as the N+1 query problem.

Spring Security

Build secure applications by understanding authentication, authorization, password encoding, roles, permissions, CSRF, CORS, JWT-based APIs, filter chains, and method security. The focus is on designing a complete security flow that protects both users and backend endpoints.

Global Exception Handling

Create one consistent error-handling layer for a REST API instead of repeating try/catch blocks in every controller. This topic covers global handlers, custom exceptions, validation failures, structured error responses, safe logging, and practical error-handling practices.

REST APIs

Design clean HTTP APIs with controllers, resources, status codes, request mappings, DTOs, pagination, validation, and versioning. You will follow a complete request from the HTTP layer through the repository and service layers, including practical CRUD and product API examples.

Validation

Keep invalid data out of your application by validating request DTOs, path and query parameters, nested objects, entity fields, service methods, and business rules. The topic also covers custom validators, database uniqueness checks, consistent validation errors, and a complete registration flow.

Testing

Verify controllers, services, repositories, and complete application flows with focused, reliable tests. Learn when to use Mockito, @WebMvcTest, @DataJpaTest, and @SpringBootTest, how to test realistic domain behavior, and how to keep test suites maintainable.

Actuator and Monitoring

Make production behavior visible with health checks, liveness and readiness probes, metrics, application information, endpoint exposure, security, custom indicators, Prometheus, Grafana, and operational logging. The goal is to monitor an application safely without exposing unnecessary management endpoints.

Deployment

Prepare a Spring Boot application for production by packaging an executable JAR, managing environment-specific configuration, containerizing with Docker, adding health checks, and planning logs, Kubernetes, CI/CD, rollback, and operational troubleshooting.