Surviving & Thriving on Day 1 with Spring Boot 3

Getting started with Spring Boot 3 is mostly the familiar Spring experience with a few hard requirements you can’t skip. The big two: Java 17 is the new minimum, and the whole framework moved from the javax.* namespace to jakarta.*. If you’re starting fresh, you barely notice. If you’re upgrading from Boot 2, those two facts explain 90% of the migration pain. Let’s get you running, then cover what changed.

What’s actually new in Spring Boot 3

• Java 17 baseline. Boot 3 won’t run on Java 8 or 11. You also get to use records, sealed classes, pattern matching, and text blocks without apology.
• Jakarta EE 9+ namespace. Every javax.persistence, javax.servlet, javax.validation import becomes jakarta.*. This is the single most common upgrade gotcha.
• Spring Framework 6 under the hood, with first-class observability (Micrometer tracing) and support for GraalVM native images for fast-starting, low-memory binaries.

If you’re new to Spring, don’t memorize this — just know your imports say jakarta, not javax.

Generate a project with Spring Initializr

The easiest way to start is start.spring.io. Choose Maven or Gradle, Java 17+, and add dependencies up front:

• Spring Web — REST APIs (see your first REST controller).
• Spring Data JPA — database persistence.
• Spring Boot DevTools — auto-restart on code changes during development.

Generate, unzip, and open it in your IDE. You get a standard project with a single @SpringBootApplication main class — run that and you have a live app.

Run it

Start the app (./mvnw spring-boot:run, or run the main class) and you’ll see the embedded Tomcat server come up on port 8080. This is Spring Boot’s whole philosophy in action: convention over configuration. Auto-configuration inspects your classpath — saw spring-boot-starter-web? It configures Tomcat, Jackson, and MVC. Saw a JDBC driver and spring-boot-starter-data-jpa? It wires a DataSource and JPA. You write business logic; Boot wires the plumbing.

A few first-day conventions worth knowing:

• Configuration lives in src/main/resources/application.properties (or application.yml).
• Spring scans for components in the package of your main class and below — keep your code under that package or things won’t be found.
• spring-boot-starter-test is included by default, with JUnit 5 and an in-memory test slice setup ready to go.

Where to go next

Once the app runs, the natural progression is: add a controller, a service, and a repository following standard Spring layering. From there, the features that make Boot production-ready:

• Profiles (application-dev.yml, application-prod.yml) for environment-specific config.
• Externalized configuration so secrets and URLs come from env vars, not source.
• Spring Boot Actuator for health checks, metrics, and readiness/liveness probes — essential before you put anything on Kubernetes.

When you’re ready to ship it, containerize it — see Dockerizing Spring Boot.

Common gotchas

• javax imports won’t resolve. You’re on Boot 3 — change them to jakarta. Most IDEs can do this with a global find-replace on imports.
• “Unsupported class file version.” You’re building with an older JDK. Boot 3 needs JDK 17+.
• App starts then exits immediately. Usually means no web starter on the classpath — add spring-boot-starter-web if you expect a running server.
• Beans not found. Component scanning only covers the main class’s package downward; misplaced packages are the usual culprit.

FAQ

Key takeaway: Getting started with Spring Boot 3 = Java 17+, jakarta.* imports, and a project from start.spring.io. Auto-configuration handles the plumbing; you add controllers/services/repositories and lean on profiles, externalized config, and Actuator when it’s time for production.