Environment-based profiles in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

How does Spring Boot select active profiles at runtime?

Consider a Spring Boot application with multiple profiles defined: dev, test, and prod. If the application is started with the JVM argument -Dspring.profiles.active=test, what will be the active profile during runtime?

A No profile is active because JVM arguments do not affect Spring profiles.

B Only the <code>test</code> profile is active.

C All profiles <code>dev</code>, <code>test</code>, and <code>prod</code> are active.

D The <code>prod</code> profile is active by default, ignoring the JVM argument.

💡 Hint

Think about how Spring Boot reads the spring.profiles.active property.

Spring Boot activates only the profile specified by spring.profiles.active. JVM arguments like -Dspring.profiles.active=test set this property, so only the test profile is active.

📝 Syntax

intermediate

Which YAML snippet correctly activates the 'prod' profile in Spring Boot?

Given the following YAML configuration, which option correctly sets the active profile to prod?

Spring Boot

spring:
  profiles:
    active: ???

A active: prod

B active: 'prod'

C active: [prod]

D

active:
  - prod

💡 Hint

Remember how simple string values are set in YAML.

The spring.profiles.active property expects a simple string or comma-separated string. The correct YAML is active: prod. Using a list is not the standard way here. Using quotes is allowed but unnecessary.

🔧 Debug

advanced

Why does the 'dev' profile not activate despite being set in application.properties?

Given these two files:

application.properties:
spring.profiles.active=dev

application-dev.properties:
logging.level.root=DEBUG

The application logs do not show DEBUG level logs. What is the most likely cause?

A The logging level property is misspelled in <code>application-dev.properties</code>.

B The <code>application-dev.properties</code> file is not named correctly.

C The <code>spring.profiles.active</code> property is overridden by an environment variable or JVM argument.

D Spring Boot does not support profile-specific properties files.

💡 Hint

Check if any external settings override the active profile.

Spring Boot allows overriding spring.profiles.active via environment variables or JVM arguments, which take precedence over application.properties. If such an override exists, the dev profile won't activate.

❓ state_output

advanced

What is the output of this Spring Boot profile conditional bean registration?

Consider this Spring Boot component:

@Component
@Profile("prod")
public class ProdService {
    public String getMessage() {
        return "Production Service";
    }
}

If the active profile is dev, what happens when the application tries to get ProdService bean?

A Spring throws a <code>NoSuchBeanDefinitionException</code> because <code>ProdService</code> is not loaded.

B Spring creates <code>ProdService</code> bean anyway ignoring the profile.

C Spring creates a proxy <code>ProdService</code> bean that returns null.

D Spring logs a warning but creates the bean.

💡 Hint

Think about how @Profile controls bean creation.

The @Profile("prod") annotation means the bean is only created if the prod profile is active. If the active profile is dev, the bean is not created, so requesting it causes NoSuchBeanDefinitionException.

🧠 Conceptual

expert

How does Spring Boot merge properties from multiple active profiles?

If a Spring Boot application activates two profiles simultaneously: dev and featureX, and both have application-dev.properties and application-featureX.properties files with overlapping keys, how does Spring Boot resolve the final property values?

A Only properties from the first profile listed in <code>spring.profiles.active</code> are used.

B Properties from all profiles are merged, and the first profile listed overrides later ones.

C Spring Boot throws an error if multiple profiles define the same property.

D Properties from the last profile listed in <code>spring.profiles.active</code> override earlier ones.

💡 Hint

Consider the order of profiles in the spring.profiles.active property.

Spring Boot loads profile-specific properties in the order they are listed in spring.profiles.active. Later profiles override properties from earlier ones if keys overlap.