Embedded server concept in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an embedded server in Spring Boot?

An embedded server is a web server (like Tomcat or Jetty) that runs inside the Spring Boot application itself, so you don't need to install or configure a separate server.

beginner

Why does Spring Boot use embedded servers by default?

Spring Boot uses embedded servers to make it easy to run applications quickly without extra setup. It packages the server with the app, so you just run one file.

beginner

Name two common embedded servers used in Spring Boot.

Tomcat and Jetty are two common embedded servers used in Spring Boot applications.

intermediate

How do you change the embedded server port in a Spring Boot application?

You can change the port by setting 'server.port' in the application.properties or application.yml file, for example: server.port=8081.

intermediate

What is the benefit of using an embedded server for deployment?

Using an embedded server means you deploy a single runnable jar or war file. This simplifies deployment and avoids server compatibility issues.

What does an embedded server in Spring Boot allow you to do?

A Disable web server functionality

B Run the application only on external servers

C Require manual server setup before running

D Run the web server inside the application without separate installation

Embedded servers run inside the Spring Boot app, so no separate server installation is needed.

Which of these is NOT a common embedded server in Spring Boot?

A GlassFish

B Jetty

C Tomcat

D Undertow

GlassFish is a full Java EE server, not commonly used as an embedded server in Spring Boot.

How can you change the default port of the embedded server?

A Change the main class name

B Modify the Java version

C Edit server.port in application.properties

D Restart the computer

Changing server.port in application.properties or application.yml sets the embedded server port.

What is a key advantage of using an embedded server for deployment?

A You must install the server separately

B You deploy a single runnable file with server included

C You cannot run the app on cloud platforms

D You need to configure the server manually every time

Embedded servers allow packaging the server inside the app, simplifying deployment.

Which file typically contains the embedded server configuration in Spring Boot?

A application.properties

B pom.xml

C README.md

D Dockerfile

application.properties or application.yml files hold configuration like server.port.

Explain what an embedded server is in Spring Boot and why it is useful.

Think about how Spring Boot packages the server with your app.

Describe how to change the port number of the embedded server in a Spring Boot app.

Look for configuration files that control server settings.

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