Introduction to Spring boot | Its Advantage over Spring MVC and Servlets

1️⃣ Servlet and Servlet Container

🔹 What is a Servlet?

  • A Servlet is a Java class that handles HTTP requests and generates HTTP responses.
  • It acts as a bridge between client and server.
  • Used mainly for building web applications.

Key Responsibilities:

  • Accept client request
  • Process business logic
  • Generate response (HTML / JSON / XML)

🔹 What is a Servlet Container?

  • A Servlet Container manages the lifecycle of servlets.
  • Examples:
    • Tomcat
    • Jetty
    • WebLogic

Responsibilities:

  • Create servlet instances
  • Manage lifecycle (init, service, destroy)
  • Handle threading
  • Map URLs to servlets using web.xml or annotations

🔹 Request–Response Flow

  1. Client sends HTTP request
  2. Request reaches Servlet Container (Tomcat)
  3. Container checks web.xml
  4. Identifies mapped servlet
  5. Invokes servlet
  6. Servlet processes and returns response

🔹 Servlet Example

public class DemoServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request,
                         HttpServletResponse response) {
        String path = request.getPathInfo();
        if ("/firstendpoint".equals(path)) {
            // logic
        }
    }
}

🔹 web.xml Mapping

<servlet>
    <servlet-name>DemoServlet</servlet-name>
    <servlet-class>DemoServlet</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>DemoServlet</servlet-name>
    <url-pattern>/demo/*</url-pattern>
</servlet-mapping>

✅ Quick Summary

  • Servlet handles request/response
  • Servlet Container manages lifecycle
  • web.xml maps URLs to servlets
  • Tight coupling and manual configuration

❓ Interview / Exam Questions

  1. What is a Servlet Container?
  2. Explain servlet lifecycle.
  3. Role of web.xml?
  4. Difference between doGet() and doPost()?

2️⃣ Problems with Traditional Servlets

🔸 Major Challenges

  • ❌ Too much XML configuration
  • ❌ Tight coupling
  • ❌ Difficult unit testing
  • ❌ Hard REST API management
  • ❌ No built-in integration support

✅ Quick Summary

  • Servlets are low-level
  • Not scalable for large apps
  • Spring solves these issues

❓ Interview / Exam Questions

  1. Why are Servlets not preferred today?
  2. What makes Servlets tightly coupled?
  3. Why is testing difficult in Servlets?

3️⃣ Spring Framework Introduction

🔹 What is Spring Framework?

  • A lightweight Java framework
  • Solves problems of Servlets
  • Based on Inversion of Control (IoC)

🔹 Core Features

  • Dependency Injection
  • Loose coupling
  • Annotation-based configuration
  • Spring MVC
  • Easy integration

✅ Quick Summary

  • Spring simplifies Java enterprise apps
  • Promotes clean architecture
  • Enables easy testing

❓ Interview / Exam Questions

  1. What is Spring Framework?
  2. Advantages of Spring?
  3. Why Spring is lightweight?

4️⃣ Dependency Injection (IoC)

🔹 Without Dependency Injection

public class Payment {
    User sender = new User(); // tight coupling
}

Problems:

  • ❌ Tight coupling
  • ❌ Cannot mock
  • ❌ Hard to extend

🔹 With Dependency Injection

@Component
public class Payment {

    @Autowired
    User sender;
}

🔹 Key Annotations

  • @Component → Bean creation
  • @Autowired → Inject dependency

🔹 Internal Working

  • Spring scans classes
  • Creates beans
  • Resolves dependencies
  • Injects at runtime

🔹 Best Practices

  • Prefer constructor injection
  • Avoid field injection in production
  • Use interfaces

✅ Quick Summary

  • DI removes tight coupling
  • Improves testability
  • Managed by Spring IoC container

❓ Interview / Exam Questions

  1. What is Dependency Injection?
  2. Difference between IoC and DI?
  3. Types of DI in Spring?

5️⃣ Spring MVC & DispatcherServlet

🔹 What is DispatcherServlet?

  • Front Controller in Spring MVC
  • Handles all incoming requests

🔹 Request Flow

  1. Request hits DispatcherServlet
  2. HandlerMapping identifies controller
  3. Controller method invoked
  4. Response returned

🔹 Controller Example

@Controller
@RequestMapping("/payment")
public class PaymentController {

    @GetMapping("/details")
    public String getDetails() {
        return "details";
    }
}

✅ Quick Summary

  • DispatcherServlet is central controller
  • Clean separation of concerns
  • Supports REST APIs

❓ Interview / Exam Questions

  1. What is DispatcherServlet?
  2. Role of HandlerMapping?
  3. Difference between Controller & RestController?

6️⃣ Spring Boot Introduction

🔹 What is Spring Boot?

  • Built on top of Spring Framework
  • Used to create production-ready apps quickly

🔹 Problems Solved by Spring Boot

  • Dependency management
  • Configuration complexity
  • Server setup

🔹 Key Features

  1. Auto Configuration
  2. Embedded Server
  3. Starter Dependencies
  4. Convention over Configuration

🔹 Main Class

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

🔹 Embedded Server

  • No WAR file
  • No external Tomcat
  • Just run main() method

🔹 REST API Example

@RestController
@RequestMapping("/myapi")
public class MyController {

    @GetMapping("/firstapi")
    public String getData() {
        return "Hello from concept and coding";
    }
}

 

✅ Quick Summary

  • Spring Boot accelerates development
  • Reduces configuration
  • Embedded server support

❓ Interview / Exam Questions

  1. Difference between Spring & Spring Boot?
  2. What is Auto Configuration?
  3. What is Embedded Server?

📌 FINAL CONCLUSION

  • Servlets are foundation but limited
  • Spring introduces IoC and MVC
  • Spring Boot makes Spring production-ready
  • Ideal for microservices & REST APIs

 

Tags:

Leave a Reply