Introduction to Spring Boot

Spring is widely used for creating scalable applications. For web applications, Spring provides Spring MVC, a commonly used module for building robust web applications. The major drawback of traditional Spring projects is that configuration can be time-consuming and overwhelming for new developers. Making an application production-ready requires significant effort.

The solution to this is "Spring Boot". Spring Boot is built on top of the Spring Framework and includes all Spring features while simplifying configuration. It has become a developer favorite due to its rapid development capabilities, allowing developers to focus on business logic instead of struggling with configurations.

Spring Boot is a microservice-based framework that enables quick development of production-ready applications. A prerequisite for learning Spring Boot is a basic understanding of the Spring Framework.

Features of Spring Boot

Spring Boot is built on top of the conventional Spring framework, providing all the features of Spring while being significantly easier to use. Here are its key features:

1. Auto-Configuration: Spring Boot eliminates the need for heavy XML configuration, which is common in traditional Spring MVC projects. Instead, everything is auto-configured. Developers only need to add the appropriate configuration to utilize specific functionalities. For example, if we want to use Hibernate (ORM), we can simply add the @Table annotation to our model/entity class and the @Column annotation to map it to database tables and columns. By 2025, Spring Boot's auto-configuration has become even smarter, utilizing AI-driven optimizations to further reduce manual setup.

2. Easy Maintenance and Creation of REST Endpoints: Creating REST APIs is incredibly easy in Spring Boot. With annotations like @RestController and @RequestMapping, developers can quickly define endpoints. By 2025, Spring Boot has introduced even more advanced annotations like @GetMapping, @PostMapping, @PutMapping, and @DeleteMapping, making REST API development more intuitive and efficient.

For example:

@RestController
@RequestMapping("/api")
public class MyController {
    @GetMapping("/hello")
    public String sayHello() {
        return "Hello, World!";
    }
}

3. Embedded Tomcat Server: Unlike traditional Spring MVC projects, where you need to manually install and configure a Tomcat server, Spring Boot comes with an embedded Tomcat server. This allows applications to be hosted directly without additional setup. By 2025, Spring Boot also supports other embedded servers like Jetty and Undertow, giving developers more flexibility based on their application requirements.

4. Easy Deployment: Spring Boot simplifies deployment by allowing applications to be packaged as JAR or WAR files. These files can be directly deployed to a Tomcat server or cloud environment. By 2025, Spring Boot has enhanced its deployment capabilities with seamless integration into Kubernetes and Docker, making it easier to deploy and scale applications in cloud-native environments.

5. Microservice-Based Architecture: Spring Boot is designed for microservices, which are small, independent modules that focus on a single functionality. For example, in a hospital management system, you might have separate services for patient registration, billing, and database management. By 2025, Spring Boot has further optimized its microservice support with features. In a monolithic system, all features are bundled into a single codebase, making it difficult to maintain and scale. In a microservice-based system, each feature is divided into smaller, independent services. This modular approach makes the system easier to maintain, debug, and deploy. Each service can be built using different technologies suited to its specific requirements.

• Reactive Programming: For building non-blocking, scalable applications.
• Distributed Tracing: For monitoring and debugging microservices.
• Service Mesh Integration: For better communication between microservices.

Evolution of Spring Boot

Spring Boot was introduced in 2013 following a JIRA request by Mike Youngstrom to simplify Spring bootstrapping.

Major Spring Boot Versions

• Spring Boot 1.0 (April 2014)
• Spring Boot 2.0 (March 2018)
• Spring Boot 3.0 (November 2022) (Introduced Jakarta EE 9+, GraalVM support)
• Latest Version (2025): Spring Boot 3.x (Enhancements in observability, native images, and containerization)

Spring Boot Architecture

To understand the architecture of Spring Boot, let’s examine its different layers and components.

Layers in Spring Boot

Spring Boot follows a layered architecture with the following key layers:

• Client Layer:
  • This represents the external system or user that interacts with the application by sending HTTPS requests.
• Controller Layer (Presentation Layer):
  • Handles incoming HTTP requests from the client.
  • Processes the request and sends a response.
  • Delegates business logic processing to the Service Layer.
• Service Layer (Business Logic Layer):
  • Contains business logic and service classes.
  • Communicates with the Repository Layer to fetch or update data.
  • Uses Dependency Injection to get required repository services.
• Repository Layer (Data Access Layer):
  • Handles CRUD (Create, Read, Update, Delete) operations on the database.
  • Extends Spring Data JPA or other persistence mechanisms.
• Model Layer (Entity Layer):
  • Represents database entities and domain models.
  • Maps to tables in the database using JPA/Spring Data.
• Database Layer:
  • The actual database that stores application data.
  • Spring Boot interacts with it through JPA/Spring Data.

Spring Boot Flow Architecture

Request Flow in Spring Boot

• A Client makes an HTTPS request (GET/POST/PUT/DELETE).
• The request is handled by the Controller, which is mapped to the corresponding route.
• If business logic is required, the Controller calls the Service Layer.
• The Service Layer processes the logic and interacts with the Repository Layer to retrieve or modify data in the Database.
• The data is mapped using JPA with the corresponding Model/Entity class.
• The response is sent back to the client. If using Spring MVC with JSP, a JSP page may be returned as the response if no errors occur.

Setup Spring Boot

1. Install Java JDK from Oracle’s official site and set up JAVA_HOME.
2. Download and install Spring Tool Suite (STS).
3. Create a new Spring Starter Project:
   • Go to File > New > Spring Starter Project.
   • Fill in the required details, add dependencies, and finish.
4. Edit the application.properties file as needed.
5. Run the main class as a Java application.