What is Spring Boot?
Spring Boot is a technology within the Spring Framework ecosystem that makes it faster and easier to develop server-side applications using the Java programming language. Spring Boot is widely used especially for building Backend applications, REST APIs, microservices, and various enterprise systems. In simple terms, Spring Framework provides powerful capabilities, but project setup and configuration can be somewhat complex. Spring Boot automates a large part of these processes, allowing developers to start projects more quickly. For example, if you want to build a REST API with Java, instead of configuring the server, libraries, and different settings from scratch, you can use a ready-made project structure provided by Spring Boot.
What Is Spring Boot Used For?
Spring Boot is mainly used to develop Java Backend applications.
With Spring Boot, it is possible to build:
- REST APIs;
- backend systems for e-commerce platforms;
- banking and financial applications;
- user management systems;
- microservices;
- various enterprise applications.
For example, in an online store, a user browses products, logs into an account, and places an order. The Frontend provides the interface that the user sees. The Backend built with Spring Boot can receive the user's request, retrieve data from the database, process business logic, and return the result to the Frontend through an API.
How Does Spring Boot Work?
Spring Boot works on top of Spring Framework and aims to reduce the need for developers to configure many components manually. When a Spring Boot application starts, it can analyze the dependencies and existing configuration in the project and automatically configure some of the required components. For example, if a web dependency is added to the project, Spring Boot can prepare the necessary infrastructure for a web application.
A simple Spring Boot application may start like this:
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
SpringApplication.run() starts the application.
@SpringBootApplication is one of the main annotations in Spring Boot and is involved in enabling application configuration, component scanning, and auto-configuration mechanisms.
What Is the Difference Between Spring and Spring Boot?
Spring Framework and Spring Boot are related, but they are not the same concept. Spring Framework is a broad framework ecosystem that provides Dependency Injection, web development, data access, security, and many other capabilities for Java applications. Spring Boot simplifies the setup and configuration of applications built with Spring.
A simple comparison:
Spring Framework → provides the core capabilities and infrastructure
Spring Boot → helps you set up and run Spring applications faster
Spring Boot does not replace Spring Framework. Instead, it uses Spring Framework's capabilities.
What Is Auto-Configuration?
Auto-Configuration is one of the core features of Spring Boot. In a traditional Spring project, developers may need to manually configure different components. Spring Boot analyzes which dependencies are included in the project and which configurations are available, then attempts to automatically configure some appropriate settings. For example, if Spring Data JPA and a compatible database driver are added, Spring Boot can automatically configure some of the infrastructure required to work with the database. When necessary, developers can override these automatic settings and write their own custom configuration.
What Is a Spring Boot Starter?
A Spring Boot Starter is a ready-made dependency package that groups together the dependencies required for a specific functionality.
For example, one of the commonly used starters for building REST APIs is:
spring-boot-starter-web
For working with a database through JPA:
spring-boot-starter-data-jpa
For Security:
spring-boot-starter-security
The purpose of starters is to reduce the need for developers to find each library separately and manually select compatible versions.
What Is an Embedded Server?
One of the advantages of Spring Boot is that an application can run with an embedded web server. For example, in Spring Boot web applications, a server such as Tomcat can run inside the application. In this case, you do not necessarily need to install a separate server and deploy the application as a WAR file. A Spring Boot application can be packaged as an executable JAR and started like this:
java -jar application.jar
This feature simplifies the deployment process and is especially useful in modern Backend and microservices projects.
What Is a Spring Boot Annotation?
In the Spring ecosystem, annotations are widely used to tell the framework what functions certain classes and methods perform.
Some of the most commonly used annotations in Spring Boot projects include:
@SpringBootApplication — defines the main startup class of the application.
@RestController — helps create a controller that handles REST API requests.
@GetMapping — maps an HTTP GET request to a specific method.
@PostMapping — handles HTTP POST requests.
@Service — identifies the service class where business logic is implemented.
@Repository — is used for the data access layer.
@Entity — defines a JPA entity associated with a database table.
These annotations help structure Spring Boot applications more effectively.
How Is a REST API Created with Spring Boot?
One of the most common uses of Spring Boot is building REST APIs.
A simple endpoint can be created like this:
@RestController
@RequestMapping("/api")
public class CourseController {
@GetMapping("/courses")
public String getCourses() {
return "Course list";
}
}
When the user sends:
GET /api/courses
the controller receives the request and returns a response. In real applications, responses are often returned in JSON format. Through REST APIs, a Spring Boot Backend can communicate with Frontend applications, mobile applications, and other systems. To learn more about APIs, you can visit JET Academy's What Is an API? glossary page.
What Are Controller, Service, and Repository?
Spring Boot projects often use a layered architecture.
A simplified structure may look like this:
Controller → Service → Repository → Database
Controller receives HTTP requests and returns responses. Service implements the application's business logic. Repository manages communication with the database. For example, a user sends a request to the /products endpoint. The Controller receives the request, the Service determines which operation should be performed, and the Repository retrieves product data from the database. This approach helps separate code according to different responsibilities and makes large projects easier to manage.
What Is Dependency Injection?
Dependency Injection is one of the core principles of Spring Framework. Imagine that ProductService needs ProductRepository to retrieve data. Instead of the Service creating the Repository object itself, Spring can provide that dependency automatically.
For example:
@Service
public class ProductService {
private final ProductRepository repository;
public ProductService(ProductRepository repository) {
this.repository = repository;
}
}
Here, ProductService does not create new ProductRepository() itself. Spring finds the appropriate dependency and provides it through the constructor. This approach helps reduce tight coupling between components and makes testing and code management easier.
How Does Spring Boot Work with Databases?
Spring Boot can work with different relational and NoSQL database systems. PostgreSQL, MySQL, and other relational databases are widely used in Java Backend projects. Database configuration can be defined in application.properties or application.yml.
For example:
spring.datasource.url=jdbc:postgresql://localhost:5432/shop
spring.datasource.username=postgres
spring.datasource.password=password
After that, Spring Data and JPA can be used to organize database operations within the application. Knowledge of SQL is also important for Backend developers because SQL is used to query and manage data in databases. For more information, you can visit the What Is SQL? page.
What Is JPA?
JPA — Java Persistence API — is a standard specification for mapping Java objects to relational database structures.
For example, in Java:
@Entity
public class Product {
@Id
private Long id;
private String name;
private BigDecimal price;
}
This class can represent Product data stored in a database.
JPA allows developers to manage many database operations directly through Java objects.
What Is Hibernate?
Hibernate is one of the most widely used implementations of the JPA specification. In Spring Boot projects, Hibernate is frequently used together with Spring Data JPA. With these technologies, developers may not need to manually write every SQL query for each CRUD operation.
For example:
public interface ProductRepository
extends JpaRepository<Product, Long> {
}
Through this Repository, developers can use ready-made methods for adding, finding, updating, and deleting data. However, understanding SQL is still important for Backend developers. SQL knowledge is required when working with database performance, relationships, queries, and optimization.
How Is Spring Boot Configured?
Spring Boot application settings are mainly stored in:
application.properties
or:
application.yml
For example:
server.port=8081
spring.application.name=shop-service
Here, the server port and application name are configured. Database connections, logging, security, and settings for various third-party services can also be managed through external configuration. This approach makes it possible to prepare different configurations for different environments without changing the application code.
What Are Spring Profiles?
Development, testing, and production environments may require different application settings. Spring Profiles allow these configurations to be separated.
For example:
application-dev.properties
application-prod.properties
A local database may be used in the development environment, while the production environment may connect to a real server database. This allows the same application to run with different configurations in different environments.
How Does Spring Boot Security Work?
Spring Security is widely used for authentication and authorization in Spring Boot applications. Authentication determines who the user is. Authorization determines which resources that user is allowed to access.
For example:
/admin
may be accessible only to users with an administrator role. Token-based authentication mechanisms such as JWT can also be used in REST API projects. JET Academy's Java Backend program also covers Authentication, Authorization, JWT, and securing API endpoints.
What Is the Relationship Between Spring Boot and Microservices?
Spring Boot is widely used to build microservices-based Backend systems. In a monolithic application, many functions may exist within the same application. In a Microservices architecture, the system is divided into smaller services, each responsible for a specific function.
For example, an e-commerce platform may have separate:
User Service
Product Service
Order Service
Payment Service
Each of these services can be developed as a separate Spring Boot application. Services can communicate with each other through REST APIs or messaging technologies such as Kafka and RabbitMQ.
How Are Spring Boot and Docker Used Together?
A Spring Boot application can run inside a Docker container. This allows the application to be packaged together with the Java runtime and other requirements in a standardized environment.
A simple process may look like this:
Spring Boot Application → JAR → Docker Image → Container
The container approach can help the application run more consistently on a developer's computer, in a testing environment, and on a production server. Docker is especially widely used in microservices projects.
What Is Spring Boot Actuator?
Spring Boot Actuator is a collection of production-oriented features that provide additional information about a running application. Actuator can be used to view information such as application health, metrics, and other operational data.
For example:
/actuator/health
can be used to check whether the application is running properly. This type of information is important for monitoring and observability in production systems.
How Are Errors Handled in Spring Boot?
Different errors can occur while processing requests in Backend applications. For example, a user may request a product that does not exist, or the submitted data may be invalid. In Spring Boot, mechanisms such as @ExceptionHandler and @ControllerAdvice can be used to manage exceptions. The goal is to return a structured response instead of an unclear server error.
For example:
{
"status": 404,
"message": "Product not found"
}
Logs, debuggers, stack traces, and tests can also be used to identify the cause of a problem. This process is closely related to the concept of Debugging in programming.
What Are the Advantages of Spring Boot?
Spring Boot can simplify many tasks in Java Backend development. Auto-configuration and starter dependencies speed up the initial project setup. The embedded server allows the application to run as a standalone application. The Spring ecosystem also provides extensive capabilities for databases, security, messaging, testing, and other functionality. In addition, Spring Boot can be used for monolithic applications, REST APIs, and microservices projects.
Are There Any Disadvantages to Spring Boot?
Spring Boot may seem complex at first for beginners. Developers need to learn several concepts together, including Spring Framework, Dependency Injection, annotations, database integration, JPA, Security, and others. Because Auto-Configuration automates many processes, developers should not simply memorize ready-made annotations. It is important to understand what the framework is doing behind the scenes. In large applications, proper architecture, database optimization, security, and monitoring still remain the developer's responsibility.
What Should You Know Before Learning Spring Boot?
Before starting Spring Boot directly, it is useful to have a strong understanding of Java fundamentals. Variables, data types, methods, classes and objects, exception handling, collections, and especially Object-Oriented Programming provide a strong foundation. After that, it is recommended to learn SQL, HTTP, APIs, and database concepts.
A possible learning path is:
Java → OOP → SQL → HTTP and REST API → Spring Framework Fundamentals → Spring Boot → JPA/Hibernate → Spring Security → Docker → Microservices
To learn Spring Boot effectively, it is important not to rely only on theoretical topics. Building practical projects such as CRUD APIs, user registration systems, e-commerce backends, and small microservices-based applications can help you understand the concepts more effectively.
If you want to learn Spring Boot, Java, PostgreSQL, REST API, Hibernate, Docker, Microservices, Kafka, RabbitMQ, and other modern Backend technologies through real-world projects, you can explore JET Academy's Java Backend Programming Course.