MediumSpring Boot#27 min readJul 11, 2026
Why Spring Boot over Spring Framework?
practice
Practice modeTest yourself instead of reading straight through
Interviewers ask this because the best answer is not that Boot is newer — it is that Boot removes the setup tax. Think of Spring Framework as the engine parts, and Spring Boot as the same engine already wired into a ready-to-drive car.
Question: Why Spring Boot over Spring Framework?
Answer: Spring Boot is usually chosen when you want to build and run Spring applications faster with less manual configuration. It sits on top of Spring Framework and gives you opinionated defaults, starter dependencies, embedded servers, and production-ready features like health checks. Spring Framework is still the core foundation; Boot mainly makes the common path much easier.
Interview-Ready Answer: I prefer Spring Boot when I want a Spring application to start quickly with minimal setup. It still uses Spring Framework under the hood, but it saves me from manually wiring dependencies, server setup, and a lot of boilerplate by using starters, auto-configuration, and embedded servers. In practice, that means I can focus on business logic and ship faster, while still getting production-ready features like actuator health endpoints.
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What Spring Boot adds
Spring Framework gives you the core platform: dependency injection, web support, transaction handling, and other building blocks. Spring Boot adds a layer of sensible defaults so you do not spend the first day choosing versions, wiring servlet containers, or writing lots of configuration. The big idea is simple: Boot makes the common case easy, while still letting you override anything when you need control.
How it works under the hood
- You start the app with
SpringApplication.run. Boot creates the SpringApplicationContext, which is the object container that holds and connects beans. - Boot scans your classes with component scanning, meaning it looks for annotations like
@RestController,@Service, and@Repositoryso it can register them automatically. - Boot then runs auto-configuration. Auto-configuration means Boot checks the classpath, existing beans, and properties, then decides what to create only if needed. This is driven by conditional rules such as
@ConditionalOnClassand@ConditionalOnMissingBean; those names mean a bean is created only when a class exists or when you have not already defined your own bean. - If you use
spring-boot-starter-web, Boot pulls in compatible web libraries and starts an embedded server such as Tomcat by default. The default HTTP port is 8080 unless you changeserver.port. - Boot loads external configuration from places like
application.properties, environment variables, and command-line arguments. That makes the same app behave differently in dev, test, and prod without changing code. - If you add Actuator, Boot exposes operational endpoints such as health and metrics. That is why Boot is popular for services that need monitoring and readiness checks out of the box.
Spring Framework vs Spring Boot
| Topic | Spring Framework | Spring Boot |
|---|---|---|
| Setup | Manual | Fast |
| Dependencies | You choose | Starters |
| Server | External | Embedded |
| Config | More wiring | Defaults |
| Ops | Add yourself | Actuator |
When Boot is the better choice
- New services: You want to start quickly and keep the codebase small.
- Microservices: You want each service to be self-contained with its own config and health checks.
- Teams: You want fewer hand-built conventions and more shared defaults.
- Production delivery: You want a smoother path from local run to deployed service.
Performance and trade-offs
Boot does not make your business logic magically faster. Its main cost is startup work: scanning the classpath, evaluating auto-configuration, and creating beans. In small apps that overhead is usually tiny; in large apps with many dependencies it can add from a few hundred milliseconds to a couple of seconds at startup. Runtime request complexity is usually unchanged, because Boot is mostly about wiring and conventions, not about changing the algorithm inside your controllers or services.
One important edge case: Boot can feel magical until you have two competing beans or conflicting starters. In those cases, the framework backs off only when you define your own bean, and the app may fail fast with clear errors. That is a feature, not a bug — it prevents hidden configuration from silently winning.
Bottom line: choose Spring Boot when speed, consistency, and production readiness matter more than hand-crafting every piece. Choose plain Spring Framework when you need very low-level control or you already have an established container and configuration model.
Real-world story
Imagine a checkout service for an online store. The team started with plain Spring Framework and manually configured the servlet setup, JSON mapping, and server deployment. It worked on one developer laptop, but staging behaved differently because one environment had a slightly different servlet mapping and another missed a health endpoint. During peak traffic, the load balancer kept sending requests to a pod that was not really ready, and customers saw timeouts at checkout.
What went wrong: the team spent time debugging plumbing instead of business logic. Logs showed repeated 404s for the checkout endpoint and readiness probe failures for /actuator/health-style checks that did not exist yet. The user impact was slow or failed orders, and the fix was moving to Spring Boot with starter dependencies, embedded server defaults, and Actuator so every environment started the same way.
Why this matters in interviews: Boot reduces the number of places where environment-specific mistakes can hide. When a service must be easy to start, easy to monitor, and easy to deploy, Boot usually wins.
Spring Boot
package com.example.bootvsframework;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Service;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@SpringBootApplication
public class BootVsFrameworkApplication {
public static void main(String[] args) {
// Spring Boot creates the ApplicationContext, wires beans, and starts the embedded server.
SpringApplication.run(BootVsFrameworkApplication.class, args);
}
@Bean
CommandLineRunner seed(ProductRepository repo) {
// A tiny seed makes the demo predictable: we can show both success and not-found paths.
return args -> {
repo.save(new Product(1L, "Keyboard", 3));
repo.save(new Product(2L, "Mouse", 0));
};
}
}
record Product(Long id, String name, int stock) { }
@Service
class ProductRepository {
private final Map<Long, Product> store = new ConcurrentHashMap<>();
public List<Product> findAll() {
return new ArrayList<>(store.values());
}
public Optional<Product> findById(Long id) {
return Optional.ofNullable(store.get(id));
}
public Product save(Product product) {
store.put(product.id(), product);
return product;
}
}
@RestController
@RequestMapping("/products")
class ProductController {
private final ProductRepository repo;
ProductController(ProductRepository repo) {
this.repo = repo;
}
@GetMapping
public List<Product> all() {
return repo.findAll();
}
@GetMapping("/{id}")
public ResponseEntity<?> one(@PathVariable Long id) {
// Optional lets us return 404 instead of throwing a server error for a missing record.
return repo.findById(id)
.<ResponseEntity<?>>map(ResponseEntity::ok)
.orElseGet(() -> ResponseEntity.status(HttpStatus.NOT_FOUND)
.body(Map.of("error", "Product not found", "id", id)));
}
@PostMapping
public ResponseEntity<?> create(@RequestBody Product product) {
// Guard clauses show that Boot still needs normal business rules; it only removes setup noise.
if (product.id() == null || product.name() == null || product.name().isBlank() || product.stock() < 0) {
return ResponseEntity.badRequest()
.body(Map.of("error", "id, name, and non-negative stock are required"));
}
// Conflict is a real edge case: without this check, a repeated POST would silently overwrite data.
if (repo.findById(product.id()).isPresent()) {
return ResponseEntity.status(HttpStatus.CONFLICT)
.body(Map.of("error", "Product already exists", "id", product.id()));
}
return ResponseEntity.status(HttpStatus.CREATED).body(repo.save(product));
}
}
Follow-up & Tricky Questions:
- Is Spring Boot replacing Spring Framework? No. Boot is built on top of Spring Framework and uses it underneath; Boot mainly adds opinionated defaults, auto-configuration, and packaging help.
- What is a Spring Boot starter? A starter is a curated dependency bundle for one job, like web or data access. It saves you from picking each library version by hand and keeps them compatible.
- How does auto-configuration decide what to create? It checks the classpath, your existing beans, and your properties. If the needed class is present and you have not already defined your own bean, Boot creates a sensible default.
- Why is an embedded server useful? It lets the app run as a self-contained process, so you can start it with one command and deploy the same artifact everywhere.
- When would you avoid Boot? If you need very fine-grained manual control, have a legacy deployment model, or already manage everything through an existing platform, plain Spring Framework may be enough.
- Does Boot automatically improve runtime performance? Not by itself. It improves developer speed and operational consistency; runtime speed still depends mostly on your code, database, and architecture.
- Gotcha: Does Boot remove the need for annotations? No. You still use Spring annotations for controllers, services, and configuration; Boot just reduces the amount of wiring around them.
- Gotcha: Can Boot app startup be slower? Yes, sometimes. Auto-configuration and scanning add startup work, but that is usually a fair trade for much lower configuration effort.
- Gotcha: Do starters include every possible library? No. They include the common, compatible set; you still add extra libraries when your feature needs them.
Common Mistakes:
- Thinking Boot is separate from Spring. Correction: Boot is a layer on top of Spring Framework, not a replacement for it.
- Saying Boot is faster at runtime by default. Correction: Boot mainly speeds up development and deployment; runtime performance depends on the app design.
- Forgetting the trade-off. Correction: Boot gives convenience, but you may need to understand auto-configuration when something is not wired the way you expect.
- Ignoring production features. Correction: Actuator, externalized configuration, and health checks are a big part of why Boot is valuable.
Memory Hook: Framework gives you the parts; Boot gives you the parts plus the wiring, server, and dashboard.
Cheat Sheet:
- Spring Framework = core Spring foundation.
- Spring Boot = opinionated layer on top.
- Boot reduces boilerplate with starters and auto-configuration.
- Boot often uses an embedded server like Tomcat.
- Boot helps with production readiness through Actuator and config support.
- Choose Boot for speed; choose plain Spring for extreme manual control.
Practice Tasks:
- Build a tiny Boot REST API with one controller and one service.
- Add a 404 path and a 400 validation check so you can explain real error handling.
- Compare a Boot startup log with a plain Spring setup and note what Boot configures for you.