Embedded server concept in Spring Boot - Mini Project: Build & Apply

Embedded Server Concept in Spring Boot

📖 Scenario: You are building a simple Spring Boot web application that runs with an embedded server. This means the server is included inside your application, so you don't need to install or configure a separate web server.This setup is common for microservices and makes deployment easier.

🎯 Goal: Create a basic Spring Boot application with an embedded Tomcat server that starts automatically and serves a simple web page.

📋 What You'll Learn

Create a Spring Boot application class with the @SpringBootApplication annotation

Add a configuration property to set the server port to 8081

Create a REST controller with a GET endpoint /hello that returns a welcome message

Ensure the application runs with the embedded server on port 8081

💡 Why This Matters

🌍 Real World

Embedded servers allow developers to package web applications with their own server, simplifying deployment and making applications portable.

💼 Career

Understanding embedded servers is essential for modern Java backend development, especially in microservices and cloud-native applications.

1

Create the Spring Boot application class

Create a class called EmbeddedServerApplication in package com.example.demo. Annotate it with @SpringBootApplication and add the main method that runs SpringApplication.run(EmbeddedServerApplication.class, args).

Spring Boot

package com.example.demo;

// Your code here

Hint

Use @SpringBootApplication on the class and add a main method that calls SpringApplication.run.

2

Configure the embedded server port

Create a file named application.properties in src/main/resources. Add the line server.port=8081 to set the embedded server port to 8081.

Spring Boot

package com.example.demo;

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

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

# Create src/main/resources/application.properties
# Add server.port=8081 inside it

Hint

The embedded server port is set in application.properties with server.port=8081.

3

Create a REST controller with a GET endpoint

Create a class called HelloController in package com.example.demo. Annotate it with @RestController. Add a method sayHello annotated with @GetMapping("/hello") that returns the string "Welcome to the embedded server!".

Spring Boot

package com.example.demo;

// Your code here to create HelloController with @RestController and @GetMapping("/hello")

Hint

Use @RestController on the class and @GetMapping("/hello") on the method that returns the welcome string.

4

Run the application with embedded server

Ensure the application class EmbeddedServerApplication has the main method that runs the Spring Boot application. This will start the embedded Tomcat server on port 8081 automatically.

Spring Boot

package com.example.demo;

// Confirm main method runs SpringApplication.run

// Your code here

Hint

The main method must call SpringApplication.run to start the embedded server.

Practice

1. What is the main advantage of using an embedded server in a Spring Boot application?

easy

A. It requires manual installation of a web server before running the app.

B. It allows the application to run standalone without needing an external server.

C. It disables HTTP support in the application.

D. It forces the use of XML configuration files.

Solution

1. Step 1: Understand embedded server purpose

   Embedded servers are included inside the app, so no external server setup is needed.

2. Step 2: Compare options

   Only It allows the application to run standalone without needing an external server. correctly states the standalone running advantage. Others describe incorrect or unrelated facts.

3. Final Answer:

   It allows the application to run standalone without needing an external server. -> Option B

4. Quick Check:

   Embedded server = standalone app [OK]

Hint: Embedded server means no external server needed [OK]

Common Mistakes:

• Thinking external server is still required
• Confusing embedded server with disabling HTTP
• Assuming XML config is mandatory

2. Which dependency is commonly used to include an embedded Tomcat server in a Spring Boot project?

easy

A. spring-boot-starter-security

B. spring-boot-starter-data-jpa

C. spring-boot-starter-test

D. spring-boot-starter-web

Solution

1. Step 1: Identify embedded server dependency

   The embedded Tomcat server comes with the spring-boot-starter-web dependency.

2. Step 2: Eliminate unrelated dependencies

   Other options relate to data, security, or testing, not embedded servers.

3. Final Answer:

   spring-boot-starter-web -> Option D

4. Quick Check:

   Web starter includes embedded Tomcat [OK]

Hint: Web starter includes embedded Tomcat by default [OK]

Common Mistakes:

• Choosing data or security starters for embedded server
• Confusing test starter with server dependency

3. Given this Spring Boot application.properties setting:
server.port=8085
What will happen when you run the app with embedded Tomcat?

medium

A. The embedded server will start on port 8085.

B. The server will ignore this and use default port 8080.

C. The app will fail to start due to invalid port.

D. The server will start on port 80.

Solution

1. Step 1: Understand server.port property

   Setting server.port changes the embedded server's listening port.

2. Step 2: Apply property effect

   Since 8085 is valid, the embedded Tomcat will start on port 8085.

3. Final Answer:

   The embedded server will start on port 8085. -> Option A

4. Quick Check:

   server.port sets embedded server port [OK]

Hint: server.port config changes embedded server port [OK]

Common Mistakes:

• Assuming default port always used
• Thinking invalid port causes failure (8085 is valid)
• Confusing port 80 as default

4. Consider this Spring Boot main class snippet:

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

If you remove the embedded server dependency, what will happen when you run this app?

medium

A. The app will start with an external server automatically.

B. The app will fail to start with a missing server error.

C. The app will start but no web server will run.

D. The app will start and embed Jetty server by default.

Solution

1. Step 1: Understand dependency role

   spring-boot-starter-web provides the embedded server. Without it, Spring Boot runs as a non-web application.

2. Step 2: Effect of removing embedded server dependency

   The app starts successfully, but no web server runs since no web dependencies are present.

3. Final Answer:

   The app will start but no web server will run. -> Option C

4. Quick Check:

   No web starter = app starts, no server [OK]

Hint: No web starter = app starts without server [OK]

Common Mistakes:

• Thinking app fails to start without server dependency
• Believing external server auto-starts
• Assuming Jetty starts by default without dependency

5. You want to switch your Spring Boot app's embedded server from Tomcat to Jetty. Which change is required?

hard

A. Exclude spring-boot-starter-tomcat and add spring-boot-starter-jetty dependency.

B. Add spring-boot-starter-jetty without excluding Tomcat.

C. Change server.port to 9090 in application.properties.

D. Add spring-boot-starter-undertow dependency only.

Solution

1. Step 1: Understand default embedded server

   Spring Boot uses Tomcat by default with spring-boot-starter-web.

2. Step 2: How to switch embedded server

   You must exclude Tomcat dependency and add Jetty starter to replace it.

3. Final Answer:

   Exclude spring-boot-starter-tomcat and add spring-boot-starter-jetty dependency. -> Option A

4. Quick Check:

   Exclude Tomcat + add Jetty = switch server [OK]

Hint: Exclude Tomcat before adding Jetty starter [OK]

Common Mistakes:

• Adding Jetty without excluding Tomcat causes conflicts
• Changing port does not switch server
• Adding Undertow starter switches to Undertow, not Jetty