Table of Contents

Background

• What is Spring?
  • Backend web framework for Java.
  • Used to build APIs and web services (monolithic or microservices).
• What is Spring Boot?
  • Wrapper around Spring. Has everything from Spring + additional features.
  • Simplifies Spring using annotations for autoconfiguration.
• Advantages of Spring Boot?
  • Most of the configuration is handled for you under the hood.
    • Just have to provide dependency configurations in properties files + annotations in code
  • Embedded HTTP server (Jetty or Tomcat).
    • No need to setup an external web server like nginx. Just run the application and a server will be created in your IDE.
  • Embedded db (H2) for easy testing
  • Actuators to check service health and status.
• Disadvantages - Opinionated framework, makes you follow preset architecture rules.

Spring Components and Scanning

• Every item that’s part of the internal structure of your app is a Spring component.
• You can mark items as Spring components with annotations
  • @Component, @Service, @Repository, @RestController are class-level annotations that mark a class as a Spring component and adds them to the Spring context.
  • @Bean is a method-level annotation that adds a method to the Spring context.
• Spring Boot will scan your code for components and use them.
• @SpringBootApplication
  • Added over the PSVM method of every Spring Boot app.
  • When the app is initialized, Spring Boot scans all classes in the current package containing the PSVM file. Then use them to configure the app.
• To scan other Spring Boot projects outside the current application and use their components, you need to scan them manually:
  1. Add outside projects you want to include as Maven/Grade dependencies.
  2. Add @ComponentScan('package.name') under @SpringBootApplication
     • Note: Different SB projects can have the same package names.

Dependency Injection

• What is dependency injection?
  • DI is a design pattern for Java classes, where you inject the class’s dependencies directly into them instead of manually assigning an object in the constructor
  • Makes it easier to unit test, by isolating the tested class from all of its dependencies.
• How to do DI
  • Declare your dependency class as a field object, but don’t assign it.
  • Add @Autowired above constructor, so Spring will implicitly handle importing dependencies.
  • In your class’s constructor, do this.field = myDependency;
• When to use DI
  • DI is crucial to the way all Spring applications are developed.
  • Use it whenever you have an external component (one that you built yourself, or imported from a library) that you want to use in the current class.

Supplemental Tools

• Spring Tool Suite
  • A set of tools added onto your IDE, to help build spring apps.
  • Supports VS Code and Eclipse