Introduction to Spring Boot

Spring Boot makes it easy to create stand-alone, production-ready Spring applications with minimal configuration. It embraces convention over configuration — you write business logic, not boilerplate.

The problem Spring Boot solves

Classic Spring required extensive XML configuration or Java-based @Configuration classes just to get a web app running. Spring Boot flips this: it auto-configures sensible defaults so you can go from zero to a running HTTP server in minutes. You override only what you need to change.

Spring Boot vs Spring Framework

Key features

• Auto-configuration: Spring Boot detects JARs on the classpath and configures beans automatically.
• Starter dependencies: spring-boot-starter-web pulls in MVC, Jackson, and an embedded Tomcat with one entry.
• Embedded server: no WAR, no external app server — just java -jar app.jar.
• Actuator: health checks, metrics, environment info via HTTP endpoints out of the box.
• Spring Initializr: generate a project skeleton at start.spring.io.

Project structure

my-app/
├── src/
│   ├── main/
│   │   ├── java/com/example/myapp/
│   │   │   ├── MyAppApplication.java    ← entry point (@SpringBootApplication)
│   │   │   ├── controller/              ← REST controllers
│   │   │   ├── service/                 ← business logic
│   │   │   ├── repository/              ← data access (Spring Data)
│   │   │   └── model/                   ← entity / DTO classes
│   │   └── resources/
│   │       ├── application.properties   ← configuration
│   │       └── static/                  ← served as-is (HTML, CSS, JS)
│   └── test/
│       └── java/com/example/myapp/      ← test classes
├── pom.xml                              ← Maven build descriptor
└── mvnw                                 ← Maven wrapper (no local Maven needed)

The entry point

package com.example.myapp;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication   // = @Configuration + @EnableAutoConfiguration + @ComponentScan
public class MyAppApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyAppApplication.class, args);
    }
}

That's it. @SpringBootApplication triggers component scanning of the package and all sub-packages, and enables auto-configuration for any starter jars on the classpath.

Maven starter

<parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>3.3.0</version>
</parent>

<dependencies>
  <!-- Web: REST, MVC, embedded Tomcat -->
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency>

  <!-- Tests: JUnit 5, Mockito, MockMvc -->
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
  </dependency>
</dependencies>

Common starters

Running the application

# Maven Wrapper (no local Maven needed)
./mvnw spring-boot:run

# Or build a fat JAR and run it directly
./mvnw clean package
java -jar target/my-app-0.0.1-SNAPSHOT.jar

# The embedded Tomcat listens on port 8080 by default
curl http://localhost:8080/