Your First Spring Boot Application

Generate a project at start.spring.io, run it, and understand what Boot set up for you.

Fresher12 min read

Read these first

Spring, IoC, and Why Boot Exists

Why this matters

Generating and running your first project proves the toolchain works before you add BookStore features.
Understanding what @SpringBootApplication enables explains later modules on auto-configuration and component scanning.
The Initializr defaults (Java 17, Maven, Jar packaging) are the baseline every article in this track assumes.

bookstore/

src/main/java/.../BookStoreApplication.java@SpringBootApplication entry point

src/main/java/.../controller/REST endpoints

src/main/java/.../service/Business logic

src/main/java/.../repository/Data access

src/main/resources/application.ymlConfiguration

pom.xmlMaven dependencies

Source code lives under src/main/java. Configuration and static assets sit in src/main/resources.

Generate the project

Visit start.spring.io with these settings:

Initializr choices for BookStore

Project — Maven
Language — Java
Spring Boot — 3.4.x
Java — 17
Dependencies — Spring Web

Download, unzip, and open in your IDE. The generated BookStoreApplication looks like:

Java

package com.example.bookstore;

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

@SpringBootApplication
public class BookStoreApplication {

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

Add a health endpoint

Create controller/HealthController.java:

Java

package com.example.bookstore.controller;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.Map;

@RestController
public class HealthController {

    @GetMapping("/health")
    public Map<String, String> health() {
        return Map.of("status", "UP", "service", "bookstore-api");
    }
}

@RestController combines @Controller and @ResponseBody — return values serialise directly to JSON.

Run the application

Java

./mvnw spring-boot:run

Console output shows Tomcat starting on port 8080:

Java

Tomcat started on port 8080 (http) with context path '/'
Started BookStoreApplication in 1.8 seconds

Verify with curl:

Java

curl http://127.0.0.1:8080/health
# {"status":"UP","service":"bookstore-api"}

What Boot set up for you

Without writing configuration, Boot provided:

Auto-configured defaults

Embedded Tomcat on port 8080
Jackson JSON serialisation for return types
Component scanning in com.example.bookstore and sub-packages
A default error page for unmapped URLs
Logging via Logback with sensible defaults

application.yml basics

Replace application.properties with YAML for readability:

Java

spring:
  application:
    name: bookstore-api

server:
  port: 8080

logging:
  level:
    com.example.bookstore: DEBUG

Spring binds spring.application.name to the process name in logs and metrics.

The startup sequence

When SpringApplication.run() executes:

Startup sequence

Creates an ApplicationContext.
Registers @SpringBootApplication as a configuration source.
Runs auto-configuration based on classpath (web starter → DispatcherServlet).
Scans for @Component classes under the main class package.
Starts the embedded web server.
Publishes ApplicationReadyEvent.

Failures at any step print a clear stack trace — read from the bottom up to find the root cause.

Project structure after first endpoint

Java

bookstore-api/
├── src/main/java/com/example/bookstore/
│   ├── BookStoreApplication.java
│   └── controller/HealthController.java
├── src/main/resources/application.yml
├── src/test/java/.../BookStoreApplicationTests.java
└── pom.xml

The generated test uses @SpringBootTest to verify the context loads:

Java

@SpringBootTest
class BookStoreApplicationTests {
    @Test
    void contextLoads() { }
}

Common first-run problems

Fixes that unblock beginners

Port 8080 in use — Set server.port=8081 or kill the conflicting process.
Java version mismatch — Boot 3.x requires Java 17; run java -version to confirm.
Controller not found (404) — Ensure the controller package is under com.example.bookstore, not a sibling package outside the scan root.
Build fails on javax imports — You are on Boot 3; use jakarta.* packages.

Package the JAR

Java

./mvnw clean package
java -jar target/bookstore-api-0.0.1-SNAPSHOT.jar

The same health endpoint responds — proof the fat JAR is deployment-ready.

Quick recall

Everything you need if you only revisit this box.

Generate projects at start.spring.io with Java 17, Maven, and the Web starter.
@SpringBootApplication enables auto-config, component scanning, and configuration registration.
SpringApplication.run() bootstraps the context and starts embedded Tomcat.
Controllers belong under the main class package so scanning finds them.
application.yml externalises port, logging, and application name.
./mvnw package produces a self-contained JAR for deployment.

Test yourself

Answer these before moving on — recall is what makes it stick.