leejunkim

Basic Dependencies

2 min read

  • Projects created with Spring Initializr include essential starter dependencies by default
  • Starters enable Spring Boot’s core goals: simplicity and auto-configuration
  • A starter dependency = a bundle that pulls in required libs a web app needs

spring-boot-starter

  • Core starter with essential Spring Boot components
    • Provides basic Bean registration, logging, and Spring Context setup
    • Serves as the foundation for all Spring Boot projects
    • Included transitively by other starters
  • Examples of Included Libraries:
    • spring-core
    • spring-context
    • spring-boot-autoconfigure
    • SLF4J + Logback (default logging system)

spring-boot-starter-test

  • A comprehensive set of integrated testing tools for Spring-based tests.
  • Includes libraries for unit testing, integration testing, mocking, and more.
  • Spring test module - spring-boot-starter-test < everything explained here lol

spring-boot-starter-web

  • Marks app as a web app
  • Includes embedded Tomcat library (tomcat-embed-core) transitively (meaning, it’s a dependency of the starter, so you get it automatically when you add the starter)

Executable JARs

Spring Boot projects are, by default, built as standalone “fat” JARs.

  • Fat JAR
    • a single, executable file that packages your project’s code, all its dependency libraries, configuration files, resources, and an embedded web server into one JAR file
    • can be executed using the java -jar command
$ ./gradlew bootJar # Or ./mvnw spring-boot:repackage for Maven
$ java -jar build/libs/myapp-0.0.1-SNAPSHOT.jar

(Reference) Internal Structure:

myapp.jar
├─ BOOT-INF/
│   ├─ classes/       <- Application classes
│   └─ lib/           <- Dependency libraries
├─ META-INF/
└─ org.springframework.boot.loader.Launcher
  • spring-boot-loader
      • Entry point that separates and loads app classes and libraries at runtime
    • Comes directly from the Spring Boot project itself.
    • Not something you manually add as a dependency like spring-boot-starter-web ⇒ - it’s automatically integrated into your executable JAR when you build your Spring Boot application using the official Spring Boot Maven Plugin or Spring Boot Gradle Plugin

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