Spring Boot and Spring Framework are closely related but serve distinct purposes in the world of Java development. Below is a comparison that highlights the key differences between the two:

1. Core Definition

• Spring Framework:
  • A comprehensive framework that provides tools, libraries, and features to build a wide variety of Java applications. It includes modules such as Spring Core, Spring MVC, Spring Security, and more.
• Spring Boot:
  • A framework built on top of the Spring Framework to simplify the development of Spring-based applications. It helps developers create standalone, production-ready applications with minimal configuration.

2. Configuration

• Spring Framework:
  • Requires extensive XML configurations or Java-based configurations to set up an application.
  • Developers need to explicitly define and configure many components (e.g., beans, data sources, etc.).
• Spring Boot:
  • Minimizes configuration by using auto-configuration and conventions over configurations.
  • Relies heavily on annotations like @SpringBootApplication, and dependencies are simplified via starters (e.g., spring-boot-starter-web, spring-boot-starter-data-jpa).
  • Enables a “just works” approach by setting up sensible defaults for most use cases.

3. Startup

• Spring Framework:
  • Applications often rely on external application servers like Tomcat or Jetty for deployment. Configuration for deployment can be complex.
• Spring Boot:
  • Provides an embedded application server (Tomcat, Jetty, or Undertow) so you can run the application directly—just like running a standalone Java program (using java -jar).
  • Simplifies startup and testing with its self-contained nature.

4. Dependencies

• Spring Framework:
  • Developers need to manually manage dependencies for different project components and modules.
• Spring Boot:
  • Uses Spring Boot starters, which are curated dependency descriptors that include the most commonly used libraries for specific types of applications.

5. Microservices

• Spring Framework:
  • Not specifically designed for microservices but can be adapted with custom configurations.
• Spring Boot:
  • Designed with microservices in mind. Provides embedded servers, REST API support, and tools like Spring Cloud to facilitate development and deployment of microservices.

6. Build and Deployment

• Spring Framework:
  • Requires build tools to configure the application and deploy it on external application servers separately.
• Spring Boot:
  • Generates standalone executable JAR or WAR files that include everything needed to run the application.

7. Learning Curve

• Spring Framework:
  • Has a steeper learning curve because developers need to understand its modules and configure them manually.
• Spring Boot:
  • Easier to get started with, thanks to its auto-configuration, starters, and reduced boilerplate code.

8. Use Cases

• Spring Framework:
  • Suitable for complex, large-scale enterprise applications where fine-grained control over configurations, and application structures is needed.
• Spring Boot:
  • Ideal for microservices architecture, cloud-native applications, rapid development, prototyping, and small to medium-sized applications.

9. Ecosystem

• Both Spring Boot and Spring Framework are part of the broader Spring ecosystem. Spring Boot internally leverages the Spring Framework, so it doesn’t replace it but rather enhances it and makes it easier to use.

Example:

• Spring Framework:
  Developers must explicitly set up dependencies, configure a dispatcher servlet, configure beans, and set up XML or Java-based configuration.
• Spring Boot:
  A single annotation (@SpringBootApplication) bootstraps the application with default settings, embedded servers, and pre-configured components.

In Summary:

Think of Spring Boot as an opinionated way to work with the Spring Framework. If you need fine-grained control and customization, you’ll likely lean toward the Spring Framework. If you prefer convenience, rapid development, and minimal configuration, Spring Boot is the better choice.