Running a Spring Boot application in Spring Boot - Performance & Optimization

Performance: Running a Spring Boot application

MEDIUM IMPACT

This affects the startup time and initial responsiveness of the web application.

Starting a Spring Boot application for web service

Spring Boot

public static void main(String[] args) {
    SpringApplication app = new SpringApplication(Application.class);
    app.setLazyInitialization(true);
    app.run(args);
}

Enables lazy initialization to delay bean creation until needed, reducing startup time.

📈 Performance Gainreduces startup blocking by up to 30-50%

Starting a Spring Boot application for web service

Spring Boot

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

Starting with default settings loads all beans and auto-configurations eagerly, causing slower startup.

📉 Performance Costblocks startup for 3-5 seconds depending on app size

Performance Comparison

Pattern	Startup Time	Memory Usage	Responsiveness	Verdict
Default eager startup	3-5 seconds	High	Delayed initial response	[X] Bad
Lazy initialization enabled	1.5-3 seconds	Moderate	Faster initial response	[OK] Good

Rendering Pipeline

When running a Spring Boot app, the JVM loads classes, initializes beans, and starts embedded server before serving requests.

→Class Loading

→Bean Initialization

→Embedded Server Startup

⚠️ BottleneckBean Initialization is most expensive due to eager loading of many components.

Core Web Vital Affected

LCP

This affects the startup time and initial responsiveness of the web application.

Optimization Tips

1Enable lazy initialization to reduce startup blocking.

2Exclude unused auto-configurations to lower memory and CPU load.

3Use JVM profilers to identify slow bean initializations.

Performance Quiz - 3 Questions

What is the main cause of slow startup in a Spring Boot application?

A Large HTML files served

B Eager loading of all beans and auto-configurations

C Slow network connection

D Too many HTTP requests

DevTools: Spring Boot Actuator and JVM Profilers

How to check: Enable Spring Boot Actuator and use JVM profilers like VisualVM to monitor startup phases and bean loading times.

What to look for: Look for long bean initialization times and high CPU usage during startup to identify bottlenecks.

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