Inside Look: Running Java Applications with Spring Boot

The Power of Spring Boot: Simplifying Java Development

Spring Boot is known for making the development process easier, and running a Spring Boot application as a "Java Application" might seem like a simple click. But there's more to it than meets the eye!

Spring Boot Loader

While it might seem like you're directly launching a Java application, Spring Boot takes control. A critical component called the Spring Boot Loader comes into play. This loader is specifically designed for Spring Boot applications and offers several advantages over a standard Java application launch.

Here's what the loader does:

  • ClassPath Scanning: It scans your classpath for specific annotations and configurations. This helps it identify the type of application you're building (web app, batch job, etc.).

  • Dependency Injection: It uses annotations to configure and inject dependencies into your beans. This removes the need for manual wiring, saving you time and effort.

  • Autoconfiguration Magic: Spring Boot is famous for its autoconfiguration capabilities. The loader analyzes your classpath and automatically configures beans based on the libraries you've included. For instance, if you have Spring WebMVC on your classpath, the loader might automatically configure a DispatcherServlet.


Contrary to what the prompt suggests, Spring Boot doesn't always launch Tomcat when you run it as a "Java Application." This behavior depends on the type of application you're building.

  • Web Applications: If you're developing a web application, the Spring Boot loader will usually detect web-related dependencies and libraries (like Spring WebMVC). In this case, it might embed a lightweight web server like Tomcat or Jetty within your application. This embedded server allows you to run your web application without needing a separate server installation.

  • Non-Web Applications: For non-web applications (like batch jobs or console apps), the loader won't start an embedded server. It focuses on creating the application context and running your application logic.

So, what are you actually running?

When you use "Run as Java Application," you're essentially launching a self-contained application. This application includes your code, the necessary libraries, and, if it's a web application, an embedded server like Tomcat. This setup is incredibly convenient because it allows you to develop and test your application quickly and easily without the need to manage a separate server installation.

Web Applications

For web applications, the embedded Tomcat server handles HTTP requests and responses, making it possible to run your web app locally just as it would run in a production environment. This means you can debug, test, and iterate on your application with minimal setup. The embedded server is configured automatically by Spring Boot, which detects the presence of web-related dependencies like Spring WebMVC and sets up the server accordingly.

Non-Web Applications

On the other hand, if you're working on a non-web application, such as a batch job or a console app, the Spring Boot loader will not start an embedded server. Instead, it will focus on creating the application context and running your application logic. This flexibility allows Spring Boot to cater to a wide range of application types, ensuring that you have the right tools and configurations for your specific needs.


In conclusion, running Java applications with Spring Boot offers significant advantages, thanks to its Spring Boot Loader, which simplifies classpath scanning, dependency injection, and autoconfiguration. Whether you're developing a web application with an embedded server like Tomcat or a non-web application, Spring Boot provides the necessary tools and configurations to streamline your development process. This versatility and ease of use make Spring Boot an invaluable framework for Java developers, enabling quick development, testing, and deployment of robust applications.

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