What is Spring Boot in Spring Boot

Introduction

Spring Boot helps you build Java applications quickly without worrying about complex setup. It makes starting and running apps easy and fast.

When you want to create a web application with minimal configuration.

When you need to build a REST API quickly.

When you want to run a standalone Java application without deploying to a separate server.

When you want to use ready-made tools and defaults to speed up development.

When you want to focus on writing business logic instead of setup details.

Syntax

Spring Boot

No special syntax to start Spring Boot. You create a main class with @SpringBootApplication and run it.

The main class uses @SpringBootApplication annotation.

You run the app by calling SpringApplication.run(MainClass.class, args).

Examples

This is the simplest Spring Boot app starter class.

Spring Boot

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

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

You can name your main class anything, but it must have @SpringBootApplication and a main method.

Spring Boot

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

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

Sample Program

This program starts a Spring Boot app and creates a simple web endpoint at '/' that returns a greeting message.

Spring Boot

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

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

@RestController
class HelloController {
    @GetMapping("/")
    public String hello() {
        return "Hello, Spring Boot!";
    }
}

Important Notes

Spring Boot uses sensible defaults to reduce setup time.

You can add features by including starter dependencies in your build file.

Spring Boot apps run as standalone Java programs with an embedded server.

Summary

Spring Boot makes Java app development fast and simple.

It uses annotations and defaults to reduce configuration.

You write a main class with @SpringBootApplication to start your app.