Why Spring Boot over plain Spring in Spring Boot

Introduction

Spring Boot makes building applications faster and easier by handling setup and configuration for you. Plain Spring requires more manual setup and can be slower to start.

When you want to quickly create a web application without writing lots of setup code.

When you prefer automatic configuration to avoid manual XML or Java config.

When you want to use embedded servers like Tomcat without extra setup.

When you want to easily package your app as a standalone executable jar.

When you want to use ready-made starter dependencies to add features quickly.

Syntax

Spring Boot

No special syntax difference in code, but Spring Boot uses @SpringBootApplication annotation to start apps easily.

@SpringBootApplication combines @Configuration, @EnableAutoConfiguration, and @ComponentScan.

Spring Boot uses opinionated defaults to reduce configuration.

Examples

This is a minimal Spring Boot app starter with automatic configuration.

Spring Boot

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

Plain Spring requires manual annotations and setup for web apps.

Spring Boot

@Configuration
@EnableWebMvc
@ComponentScan
public class MyConfig {
  // manual Spring setup
}

Sample Program

This Spring Boot app starts quickly with embedded server and serves a simple web page at root URL.

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

Important Notes

Spring Boot reduces boilerplate and speeds up development.

You can still use plain Spring if you want full control, but it takes more setup.

Spring Boot starters help add features like web, data, security easily.

Summary

Spring Boot automates setup and configuration for faster app building.

It uses embedded servers and starter dependencies for convenience.

Plain Spring requires more manual configuration and setup.

Practice

1. What is a main advantage of using Spring Boot over plain Spring Framework?

easy

A. It requires manual XML configuration for all components.

B. It does not support dependency injection.

C. It provides automatic configuration and embedded servers to simplify setup.

D. It only works with legacy Java versions.

Solution

1. Step 1: Understand Spring Boot features

   Spring Boot offers automatic configuration and embedded servers to reduce manual setup.

2. Step 2: Compare with plain Spring

   Plain Spring requires manual XML or Java config and separate server setup.

3. Final Answer:

   It provides automatic configuration and embedded servers to simplify setup. -> Option C

4. Quick Check:

   Spring Boot simplifies setup = B [OK]

Hint: Spring Boot automates config and server setup [OK]

Common Mistakes:

• Thinking Spring Boot needs manual XML config
• Believing Spring Boot lacks dependency injection
• Assuming Spring Boot only supports old Java versions

2. Which of the following is the correct way to start a Spring Boot application?

easy

A. public void start() { Spring.run(App.class); }

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

C. public static void main(String[] args) { Application.run(App.class); }

D. public static void main(String[] args) { BootApplication.run(App.class); }

Solution

1. Step 1: Recall Spring Boot startup method

   Spring Boot apps start with SpringApplication.run() inside main().

2. Step 2: Check options for correct syntax

   Only public static void main(String[] args) { SpringApplication.run(App.class, args); } uses correct method and signature.

3. Final Answer:

   public static void main(String[] args) { SpringApplication.run(App.class, args); } -> Option B

4. Quick Check:

   Spring Boot starts with SpringApplication.run() = A [OK]

Hint: Spring Boot apps start with SpringApplication.run() [OK]

Common Mistakes:

• Using incorrect method names like Application.run()
• Missing static main method signature
• Confusing Spring Boot with other frameworks

3. Given this Spring Boot application snippet, what will happen when you run it?

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

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

medium

A. The application starts with an embedded server and default configuration.

B. The application throws a compilation error due to missing annotations.

C. The application requires manual server setup before running.

D. The application runs but does not start any server.

Solution

1. Step 1: Identify @SpringBootApplication role

   This annotation enables auto-configuration and component scanning.

2. Step 2: Understand SpringApplication.run behavior

   It starts the app with embedded server and default settings.

3. Final Answer:

   The application starts with an embedded server and default configuration. -> Option A

4. Quick Check:

   @SpringBootApplication + SpringApplication.run = embedded server start [OK]

Hint: @SpringBootApplication triggers auto-config and embedded server [OK]

Common Mistakes:

• Thinking manual server setup is needed
• Assuming missing annotations cause errors here
• Believing app runs without server

4. You wrote a Spring Boot app but it fails to start with this error: ClassNotFoundException: org.springframework.boot.SpringApplication. What is the likely cause?

medium

A. You did not annotate your main class with @SpringBootApplication.

B. You used the wrong main method signature.

C. You are running the app with an unsupported Java version.

D. You forgot to add Spring Boot starter dependencies in your build file.

Solution

1. Step 1: Analyze the error message

   ClassNotFoundException means the class is missing from the project dependencies.

2. Step 2: Identify missing dependency cause

   SpringApplication class is part of spring-boot package, so missing starter dependencies cause this.

3. Final Answer:

   You forgot to add Spring Boot starter dependencies in your build file. -> Option D

4. Quick Check:

   Missing Spring Boot dependencies = ClassNotFoundException [OK]

Hint: ClassNotFoundException usually means missing dependencies [OK]

Common Mistakes:

• Blaming wrong main method signature
• Assuming missing annotation causes ClassNotFoundException
• Thinking Java version causes missing class

5. You want to create a REST API quickly. Why is Spring Boot preferred over plain Spring for this task?

hard

A. Spring Boot provides starter dependencies and embedded servers to launch REST APIs fast.

B. Plain Spring automatically configures REST endpoints without extra setup.

C. Spring Boot requires manual XML configuration for REST controllers.

D. Plain Spring includes embedded servers by default.

Solution

1. Step 1: Understand REST API setup in Spring Boot

   Spring Boot offers starter dependencies and embedded servers to reduce setup time.

2. Step 2: Compare with plain Spring requirements

   Plain Spring needs manual configuration and external server setup for REST APIs.

3. Final Answer:

   Spring Boot provides starter dependencies and embedded servers to launch REST APIs fast. -> Option A

4. Quick Check:

   Spring Boot simplifies REST API setup = D [OK]

Hint: Spring Boot starters + embedded server speed REST API creation [OK]

Common Mistakes:

• Thinking plain Spring auto-configures REST endpoints
• Believing Spring Boot needs manual XML config
• Assuming plain Spring has embedded servers by default