How to Build Your First Spring Boot App the Right Way

What do I need to know before starting Spring Boot?

Before writing a single line of Spring Boot code, confirm two prerequisites: solid Java OOP knowledge (classes, methods, and especially interfaces) and familiarity with relational databases and basic SQL. This methodology flags these explicitly because gaps cause confusion downstream. Dependency injection and programming against interfaces assume you're comfortable with abstraction, and the data layer assumes you can read SQL. If either is shaky, close the gap first — don't treat prerequisites as optional.

How do I set up my environment and generate a project?

Install the latest stable JDK and verify it with `java -version`. Use IntelliJ IDEA Ultimate, not Community Edition — Community lacks the built-in Spring Boot generator and the tools you'll rely on constantly. Inside IntelliJ, use the built-in generator (not start.spring.io, to avoid context switching). Set Language=Java, Build Tool=Maven, Spring Boot=latest stable (never a snapshot), a reverse-domain Group ID like `com.codewithmosh`, and your project name as the Artifact. Enable Git at this step and leave dependency selection for later.

Then validate the generated structure before touching code: `.idea/` (IntelliJ config, never edit), `.mvn/` and `mvnw`/`mvnw.cmd` (the Maven Wrapper), `pom.xml` (the heart of the project), `src/main/java` (your code), `src/main/resources/application.properties` (config), and `src/test/java` (tests). Your entry point is the class containing `SpringApplication.run()`.

How do I add dependencies and wire beans correctly?

Use IntelliJ's dependency search (Cmd+N → Dependency) instead of hand-editing pom.xml, then click the Maven sync icon to download. The single most important beginner habit: delete the `` tag from every Spring Boot starter. Your project inherits from `spring-boot-starter-parent`, which supplies tested, compatible versions automatically. Keeping versions invites conflicts later.

When one class needs another, don't instantiate it with `new`. Instead, extract an interface (Refactor → Extract → Interface), annotate only the concrete class with `@Service`, `@Repository`, `@Controller`, or `@Component`, and inject the interface through a constructor. If your class has exactly one constructor, you don't even need `@Autowired` — Spring infers it. This is called constructor injection, and it's the default because a missing dependency crashes the app loudly at startup rather than silently with a NullPointerException later.

Why does this approach matter for a beginner?

Because the habits you form now stick. Field injection looks convenient but hides dependencies and breaks testing. Setter injection for required dependencies leaves fields null. Annotating an interface produces no bean at all. This methodology steers you away from all of these from day one, so your first app is already decoupled and testable. It also teaches restraint — don't extract an interface where there's only ever one implementation, or you'll create an over-engineered mess. Apply the Open Closed Principle with common sense.

Once your beans are wired, add a `@Controller` with `@RequestMapping("/")`, return a view name, drop static files in `src/main/resources/static/`, and run with Ctrl+R or `./mvnw spring-boot:run`. Visit `http://localhost:8080` and you have a working, professionally structured Spring Boot app.

Next step: Generate a fresh project in IntelliJ Ultimate, validate every folder against the checklist above, then wire your first service using constructor injection before adding any business logic.