Running a Spring Boot application in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start the Spring Boot application.

Spring Boot

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

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

Arun

Bexecute

Claunch

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

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

Forgetting to pass the application class and args.

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

2fill in blank

medium

Complete the annotation to mark the main class as a Spring Boot application.

Spring Boot

@[1]
public class MyApplication {
    // main method here
}

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

AComponent

BSpringBootApplication

CService

DConfiguration

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Component or @Service which are for beans, not the main application.

Forgetting to annotate the main class.

The @SpringBootApplication annotation marks the main class as the entry point for Spring Boot.

3fill in blank

hard

Fix the error in the main method to correctly start the application.

Spring Boot

public static void main(String[] args) {
    SpringApplication.[1];
}

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

Arun(MyApplication.class, args)

Bstart()

Claunch()

Dexecute()

Attempts:

3 left

💡 Hint

Common Mistakes

Calling run() without parameters causes errors.

Using non-existent methods like start or launch.

The run method requires the application class and arguments to start properly.

4fill in blank

hard

Fill both blanks to create a Spring Boot application main class with the correct annotation and main method call.

Spring Boot

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

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

ASpringBootApplication

BComponent

Crun

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong annotations like @Component.

Using non-existent methods like start.

The main class must be annotated with @SpringBootApplication and start with SpringApplication.run().

5fill in blank

hard

Fill all three blanks to create a Spring Boot main class with annotation, main method, and run call.

Spring Boot

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

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

ASpringBootApplication

BMyApplication

Crun

DApplication

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching class names.

Using wrong annotation or method names.

The class is annotated with @SpringBootApplication, named MyApplication, and started with SpringApplication.run().

Practice

1. What is the main method used for in a Spring Boot application?

easy

A. To configure the database connection

B. To start the Spring Boot application using SpringApplication.run()

C. To define REST endpoints

D. To create HTML views

Solution

1. Step 1: Understand the role of the main method

   The main method is the entry point of any Java application, including Spring Boot apps.

2. Step 2: Identify what SpringApplication.run() does

   SpringApplication.run() starts the Spring Boot application by initializing the Spring context and components.

3. Final Answer:

   To start the Spring Boot application using SpringApplication.run() -> Option B

4. Quick Check:

   Main method starts app = To start the Spring Boot application using SpringApplication.run() [OK]

Hint: Main method always starts Spring Boot with SpringApplication.run() [OK]

Common Mistakes:

• Confusing main method with configuration tasks
• Thinking main method defines endpoints
• Assuming main method creates UI views

2. Which of the following is the correct way to run a Spring Boot application from the command line using Maven?

easy

A. mvn spring-boot:run

B. mvn run spring-boot

C. mvn start boot

D. mvn execute springboot

Solution

1. Step 1: Recall Maven command for Spring Boot

   The standard Maven command to run a Spring Boot app is 'mvn spring-boot:run'.

2. Step 2: Check other options for correctness

   Other options do not follow Maven or Spring Boot plugin syntax and will cause errors.

3. Final Answer:

   mvn spring-boot:run -> Option A

4. Quick Check:

   Maven run command = mvn spring-boot:run [OK]

Hint: Use 'mvn spring-boot:run' to run Spring Boot apps with Maven [OK]

Common Mistakes:

• Mixing up command order
• Using invalid Maven goals
• Typing incomplete commands

3. Given this main class, what happens when you run it?

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

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

medium

A. The application starts and initializes Spring Boot context

B. The application throws a compilation error

C. The application runs but does not start Spring Boot

D. The application starts but immediately exits without running

Solution

1. Step 1: Analyze the main method code

   The main method calls SpringApplication.run() with the class annotated by @SpringBootApplication.

2. Step 2: Understand @SpringBootApplication effect

   This annotation enables auto-configuration and component scanning, so Spring Boot context starts properly.

3. Final Answer:

   The application starts and initializes Spring Boot context -> Option A

4. Quick Check:

   SpringApplication.run() starts app = The application starts and initializes Spring Boot context [OK]

Hint: SpringApplication.run() with @SpringBootApplication starts app [OK]

Common Mistakes:

• Thinking @SpringBootApplication is optional
• Assuming code throws error without extra config
• Believing app runs but does not start Spring context

4. You try to run your Spring Boot app but get this error: java.lang.NoClassDefFoundError: org/springframework/boot/SpringApplication. What is the most likely cause?

medium

A. The Java version is too new for Spring Boot

B. The main method is missing in the application class

C. The Spring Boot dependency is missing from the project

D. The application.properties file is empty

Solution

1. Step 1: Understand the error meaning

   NoClassDefFoundError means the JVM cannot find the SpringApplication class at runtime.

2. Step 2: Identify cause of missing class

   This usually happens if the Spring Boot dependency is not included or not properly loaded in the project.

3. Final Answer:

   The Spring Boot dependency is missing from the project -> Option C

4. Quick Check:

   NoClassDefFoundError = missing dependency [OK]

Hint: NoClassDefFoundError usually means missing dependency [OK]

Common Mistakes:

• Blaming missing main method for this error
• Thinking empty config files cause class errors
• Assuming Java version causes missing class

5. You want to run your Spring Boot app as a standalone jar. Which command correctly runs the jar file named app.jar?

medium

A. mvn run app.jar

B. java run app.jar

C. gradle run app.jar

D. java -jar app.jar

Solution

1. Step 1: Recall how to run a jar file in Java

   The standard command to run an executable jar is 'java -jar filename.jar'.

2. Step 2: Check other options for correctness

   The mvn and gradle commands are for build tools, not for running jar files directly. 'java run app.jar' is invalid Java command syntax.

3. Final Answer:

   java -jar app.jar -> Option D

4. Quick Check:

   Run jar with 'java -jar' = java -jar app.jar [OK]

Hint: Run jar files with 'java -jar filename.jar' [OK]

Common Mistakes:

• Using build tool commands to run jar directly
• Omitting '-jar' option
• Typing invalid Java commands