Spring Boot

Spring Boot is the most widely used Java framework for building production server applications. Built on top of the broader Spring Framework, Spring Boot adds auto-configuration, an embedded application server, and a "starter" dependency system so developers can launch a working web application in minutes instead of wiring XML configuration by hand.

Core pieces

• Auto-configuration. Spring Boot inspects the classpath and configures beans automatically (data source, web server, security).
• Starters. Curated dependency groups: spring-boot-starter-web, -data-jpa, -security, -actuator, and many more.
• Embedded server. Tomcat, Jetty, or Undertow ships inside the application jar; one binary boots the app.
• Spring Data. Repository abstractions for JPA, MongoDB, Redis, Cassandra, and many other stores.
• Spring Security. Authentication and authorization with OAuth 2.0, OIDC, SAML, and method-level checks.
• Actuator. Production endpoints: health, metrics, info, env, threaddump, often integrated with Prometheus and Micrometer.

Where it fits

• Microservices in Java or Kotlin (Spring Boot is JVM)
• Enterprise back-ends needing mature security, transaction, and integration stories
• Reactive applications via Spring WebFlux