Embedded server concept in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a Spring Boot application with an embedded server.

Spring Boot

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

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.[1](Application.class, args);
    }
}

Drag options to blanks, or click blank then click option'

Aexecute

Bstart

Claunch

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using methods like start() or launch() which do not exist in SpringApplication.

Forgetting to pass the application class as the first argument.

The SpringApplication.run() method starts the Spring Boot application with the embedded server.

2fill in blank

medium

Complete the code to specify the embedded server port in application.properties.

Spring Boot

server.[1]=8081

Drag options to blanks, or click blank then click option'

Aport

Bhost

Caddress

Durl

Attempts:

3 left

💡 Hint

Common Mistakes

Using server.host or server.address which are not valid for port configuration.

Setting the port in code instead of properties file.

The property server.port sets the port number for the embedded server in Spring Boot.

3fill in blank

hard

Fix the error in the code to create a REST controller with embedded server.

Spring Boot

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {
    @GetMapping("/hello")
    public String [1]() {
        return "Hello, World!";
    }
}

Drag options to blanks, or click blank then click option'

Ahello

BgetHello

CsayHello

DhelloWorld

Attempts:

3 left

💡 Hint

Common Mistakes

Using invalid method names or names that conflict with annotations.

Omitting the method name entirely.

The method name can be any valid Java method name. getHello is a clear name for a GET endpoint.

4fill in blank

hard

Fill both blanks to configure the embedded Tomcat server's max threads and port in application.properties.

Spring Boot

server.[1]=9090
server.tomcat.threads.[2]=200

Drag options to blanks, or click blank then click option'

Aport

Bmax

Cmin-spare

Daddress

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing port with address or host.

Using min-spare instead of max for max thread configuration.

server.port sets the port number, and server.tomcat.threads.max sets the maximum threads for the embedded Tomcat server.

5fill in blank

hard

Fill all three blanks to create a Spring Boot application class with embedded server and a REST endpoint.

Spring Boot

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
@RestController
public class [1] {
    public static void main(String[] args) {
        SpringApplication.[2]([3].class, args);
    }

    @GetMapping("/greet")
    public String greet() {
        return "Greetings from embedded server!";
    }
}

Drag options to blanks, or click blank then click option'

AMyApplication

Brun

CApplication

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching class names in main method and class declaration.

Using incorrect method names instead of run().

The class name MyApplication is used consistently. The SpringApplication.run() method starts 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