Why is Spring Boot Called Opinionated?

Introduction

If you're learning Spring Boot, you’ve probably heard it being described as "opinionated." But what does that mean? In software development, an opinionated framework provides default configurations and conventions that guide developers toward best practices. This is exactly what Spring Boot does. It makes decisions for you, so you can focus on writing code instead of spending time configuring the environment. In this blog post, we’ll explain why Spring Boot is called opinionated and how this feature benefits developers.

What Does "Opinionated" Mean in Software?

An opinionated framework comes with predefined configurations and defaults. It assumes the most common use cases and settings that developers need and sets them up for you automatically. This approach contrasts with unopinionated frameworks, where you need to configure everything from scratch based on your preferences.

Being opinionated doesn’t mean you can’t customize things. It simply means the framework starts with a certain way of doing things, but you can change or override those defaults if needed.

Why is Spring Boot Opinionated?

Spring Boot is considered opinionated because it automatically configures many aspects of your application based on the dependencies you include in your project. Instead of requiring you to manually configure each part of your application, Spring Boot makes decisions about the best setup and applies those configurations for you.

Key Reasons Spring Boot is Opinionated:

1. Auto-Configuration

   One of the biggest reasons Spring Boot is called opinionated is its auto-configuration feature. When you create a Spring Boot project and add certain dependencies (such as a database or web framework), Spring Boot automatically configures them for you.

   For example:

   • If you add a database dependency like H2 or MySQL, Spring Boot will automatically configure the database connection.
   • If you include Spring Web, Spring Boot sets up an embedded server (like Tomcat) and configures it to handle HTTP requests.

   You don’t need to write configuration files or deal with manual setup—Spring Boot makes an assumption about what you need and configures it accordingly.

2. Starter Dependencies

   Spring Boot provides starter dependencies, which are pre-packaged sets of libraries and tools that are commonly used together. This makes it easier to get started with a project. For example, if you want to build a web application, you can simply include the spring-boot-starter-web dependency, and it will automatically include everything you need, such as:

   • Spring MVC for web functionality
   • Tomcat for the embedded server
   • Jackson for JSON parsing
   • Logging libraries

   The opinionated nature of Spring Boot means it assumes which dependencies you’ll need and sets them up for you. This reduces the burden of manually choosing and configuring individual libraries.

3. Embedded Web Servers

   In traditional Spring applications, you’d need to set up and configure an external web server like Tomcat or Jetty. Spring Boot simplifies this by including embedded web servers as part of the project setup. You don’t need to install or configure a separate server—Spring Boot makes the decision for you and includes the most commonly used web server, Tomcat, by default.

   This "opinion" helps developers get their applications running quickly, without worrying about setting up and configuring web servers.

4. Production-Ready Features

   Spring Boot includes a variety of production-ready features such as health checks, metrics, and monitoring tools out of the box. This is part of Spring Boot’s opinionated approach: it assumes you’ll need these features when deploying your application and sets them up for you.

   For example:

   • The Spring Boot Actuator module automatically configures endpoints for checking application health, viewing metrics, and gathering information about the app’s environment.
   • Logging is pre-configured with sensible defaults, so you don’t have to manually set up loggers.

   These production-ready features show Spring Boot’s opinionated nature by assuming what tools you’ll need for production and automatically integrating them into your project.

5. Convention Over Configuration

   Spring Boot follows the principle of “convention over configuration”. This means that instead of requiring developers to explicitly configure everything, it provides reasonable defaults that follow best practices. For example:

   • By default, Spring Boot will look for an application.properties or application.yml file to configure settings.
   • If you don’t define certain settings (like port numbers), Spring Boot will assume default values.

   This makes development faster because you don’t need to spend time configuring things that have widely accepted standards or defaults. However, if you need to customize these settings, Spring Boot allows you to override them.

Benefits of an Opinionated Framework

1. Faster Development

One of the biggest advantages of using an opinionated framework like Spring Boot is that it speeds up development. You don’t need to spend hours setting up your project or configuring libraries manually. Spring Boot takes care of these details for you, allowing you to focus on writing business logic.

2. Reduces Boilerplate Code

By handling much of the configuration for you, Spring Boot reduces the amount of boilerplate code you need to write. For example, setting up database connections, web servers, and logging are all handled automatically, saving you time and effort.

3. Best Practices by Default

Because Spring Boot is opinionated, it follows best practices out of the box. It assumes what most developers would want in a standard application setup and configures things accordingly. This ensures that even beginners are following good practices without having to know every detail.

4. Easily Customizable

While Spring Boot makes assumptions, it doesn’t lock you into them. If you want to customize or override any of the default configurations, you can do so easily. Spring Boot provides flexibility for developers who want more control over their application.

When Might Opinionated Be a Drawback?

While being opinionated is helpful for most scenarios, it can sometimes be limiting if you have very specific requirements or want complete control over your project’s configuration. In those cases, traditional Spring Framework (without Boot) may be a better option, allowing for full customization without default configurations.

However, for the vast majority of projects, Spring Boot’s opinionated approach saves time and reduces complexity.

Conclusion

Spring Boot is called opinionated because it makes decisions for you by providing default configurations, auto-configuration, and starter dependencies. This helps developers get started quickly without needing to configure every part of their project manually. The opinionated nature of Spring Boot leads to faster development, less boilerplate code, and a smoother experience overall. While you still have the option to customize things, Spring Boot’s defaults guide you toward best practices, making it an excellent choice for most Java developers.