Introduction to Spring Boot

Getting Started with Spring Boot

Spring is a powerful framework for building Java applications, but setting up a new project can involve a lot of repetitive configuration. Spring Boot is an extension of the Spring Framework designed to get you up and running as quickly as possible.

Spring Boot is an open-source Java-based framework used to create stand-alone, production-grade Spring-based applications with minimal effort.

It takes an "opinionated" view of the Spring platform, which means it makes smart assumptions about what you need. This allows you to create standalone applications with minimal fuss, so you can focus on writing code that matters.

Convention Over Configuration

The core philosophy behind Spring Boot is "convention over configuration." This means the framework provides sensible default settings based on common development practices. Instead of writing pages of XML or Java configuration files to connect a database or set up a web server, you often don't have to do anything at all.

Spring Boot uses a feature called auto-configuration. It inspects the libraries (JAR files) you've added to your project and automatically configures the necessary components. For example, if you include the spring-boot-starter-web dependency, Spring Boot assumes you're building a web application and configures things like a dispatcher servlet and a web server for you.

If Spring Boot finds a database driver like H2 on your project's classpath, it will automatically set up an in-memory database. No manual setup required for a basic connection.

This approach drastically reduces boilerplate code and setup time. You can always override the defaults if you need to, but for most standard cases, Spring Boot's conventions work perfectly out of the box.

Embedded Servers

Traditionally, Java web applications were packaged as WAR (Web Application Archive) files and deployed to an external application server like Tomcat or JBoss. This meant you had to install, configure, and maintain a separate server environment.

Spring Boot simplifies this by popularizing the use of embedded servers. The web server is packaged inside your application as just another library.

With Spring Boot, you can run your application as a standalone JAR file, thanks to its embedded server (like Tomcat, Jetty, or Undertow).

This makes your application completely self-contained. To run it, you just need Java installed. You can start your entire application with a single command: java -jar my-application.jar. This is a huge benefit for development, testing, and deployment, especially in modern cloud and container-based environments.

Your First Application

Before you start, make sure you have the necessary tools. Spring Boot projects can be built with either Maven or Gradle, which are popular build automation tools in the Java ecosystem.

Component	Requirement
Java	Version 17 or higher recommended
Build Tool	Apache Maven 3.6.3+ or Gradle 7.5+

The easiest way to create a new Spring Boot project is with the Spring Initializr. This is a web-based tool that generates a complete project structure for you.

Here’s how to create a simple "Hello World" web application:

Go to start.spring.io.
Choose Maven or Gradle as your project type.
Leave the default project metadata or customize it (Group, Artifact, etc.).
In the "Dependencies" section, click Add Dependencies and search for and select Spring Web.
Click Generate. A .zip file containing your project will be downloaded.

Unzip the file, open it in your favorite IDE, and find the main application class. It will look something like this:

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {

	public static void main(String[] args) {
		SpringApplication.run(DemoApplication.class, args);
	}

}

The @SpringBootApplication annotation is a convenience that adds several other annotations. It tells Spring Boot that this is the main configuration class and enables auto-configuration and component scanning.

To see it in action, let's add a simple REST controller. Create a new class called HelloController:

package com.example.demo;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    @GetMapping("/")
    public String sayHello() {
        return "Hello, World!";
    }
}

Now, run the main method in your DemoApplication class from your IDE or by using your build tool. The embedded Tomcat server will start, and your application will be running on port 8080. Open a web browser and navigate to http://localhost:8080. You should see the message "Hello, World!" on the screen.

That's it! You've just created and run your first stand-alone Spring application.

Spring Boot Essentials