Spring Boot

Spring Boot is the usual way to start a project on the Spring framework, the long-standing Java application framework. It solves Spring's setup problem: instead of wiring the framework, a web server and libraries together by hand, you pick "starter" dependencies and Spring Boot configures them for you, with no code generation or XML.

How it works: you generate a project (Java or Kotlin, Maven or Gradle) at start.spring.io, and the app runs as a stand-alone program with Tomcat or Jetty embedded, so there is no separate server to install or WAR file to deploy. Auto-configuration looks at what is on the classpath and sets up beans accordingly; you override defaults through properties files or your own beans. Spring Boot 4 needs Java 17 or later.

What you get: database access through Spring Data JPA with Hibernate, Spring Data JDBC, JdbcClient, jOOQ or reactive R2DBC, with HikariCP connection pooling by default; Flyway or Liquibase migrations that run on startup; Spring Security, which locks down every endpoint as soon as it is added and supports OAuth2 and SAML; and Actuator endpoints for health checks, metrics and logger settings. Apps can also be compiled to GraalVM native executables.

The limits: Spring's annotations, dependency injection and auto-configuration are a lot to learn, and when something is configured for you it is not always obvious from where. On the JVM, Spring's own docs say native images start much faster and use less memory; getting those benefits means ahead-of-time compilation, a fixed classpath and restrictions on runtime-dependent features such as @Profile. There is no built-in admin panel or frontend framework.