Profile-based configuration in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

Spring Boot Profile Activation Behavior

Given a Spring Boot application with application.properties and application-dev.properties files, and the active profile set to dev, what will be the value of the property app.message if application.properties has app.message=Hello from default and application-dev.properties has app.message=Hello from dev?

A Hello from default

B An error occurs because of conflicting properties

C Hello from dev

D The property <code>app.message</code> will be empty

💡 Hint

Spring Boot uses the active profile properties to override default properties.

When a profile is active, Spring Boot loads application.properties first, then overrides with application-{profile}.properties. So app.message from application-dev.properties replaces the default.

📝 Syntax

intermediate

Correct Syntax for Profile-Specific Bean Declaration

Which of the following is the correct way to declare a Spring bean that only loads when the test profile is active?

A

@Bean
@Profile({test})
public DataSource testDataSource() { return new DataSource(); }

B

@Bean
@Profile(test)
public DataSource testDataSource() { return new DataSource(); }

C

@Bean
@Profile('test')
public DataSource testDataSource() { return new DataSource(); }

D

@Bean
@Profile("test")
public DataSource testDataSource() { return new DataSource(); }

💡 Hint

Profile annotation requires a string value with double quotes.

The @Profile annotation requires the profile name as a string in double quotes. Option D uses the correct syntax.

🔧 Debug

advanced

Why Does the Profile-Specific Property Not Load?

A developer has application.properties and application-prod.properties. They set spring.profiles.active=prod in application.properties. But the properties from application-prod.properties are not loaded at runtime. What is the most likely cause?

A The <code>spring.profiles.active</code> property must be set as a command-line argument or environment variable, not inside <code>application.properties</code>.

B Spring Boot does not support multiple property files for profiles.

C The profile name <code>prod</code> is misspelled in the filename.

D Setting <code>spring.profiles.active</code> inside <code>application.properties</code> disables profile-specific loading.

💡 Hint

Active profiles set inside application.properties can cause loading order issues.

Setting spring.profiles.active inside application.properties can cause Spring Boot to load properties incorrectly because it reads application.properties before knowing the active profile. It is recommended to set active profiles via command-line or environment variables.

❓ state_output

advanced

Output of Bean Initialization with Multiple Active Profiles

Consider a Spring Boot app with two active profiles: dev and qa. There are two beans defined with @Profile("dev") and @Profile("qa") respectively. What happens when the app starts?

A Only the bean with <code>@Profile("dev")</code> loads because it is first in the list.

B Both beans load because both profiles are active.

C Neither bean loads because Spring Boot supports only one active profile at a time.

D An error occurs due to conflicting beans with different profiles.

💡 Hint

Spring Boot supports multiple active profiles simultaneously.

When multiple profiles are active, Spring Boot loads beans for all active profiles. So both beans annotated with @Profile("dev") and @Profile("qa") will be created.

🧠 Conceptual

expert

Understanding Profile-Specific Property Precedence

In Spring Boot, if you have application.properties, application-dev.properties, and application-local.properties, and you activate both dev and local profiles, which property file has the highest precedence when properties conflict?

A The last profile listed in <code>spring.profiles.active</code> has the highest precedence

B <code>application-dev.properties</code> because it is the first profile alphabetically

C <code>application.properties</code> because it is the base configuration

D <code>application-local.properties</code> because it is loaded last

💡 Hint

Order of profiles in spring.profiles.active affects property overriding.

When multiple profiles are active, Spring Boot loads application.properties first, then profile-specific files in the order they appear in spring.profiles.active. Later profiles override earlier ones.

Practice

1. What is the main purpose of using profiles in Spring Boot configuration?

easy

A. To switch application settings easily for different environments

B. To write Java code faster

C. To create user interfaces

D. To manage database connections manually

Solution

1. Step 1: Understand what profiles do

   Profiles allow you to have different settings for different environments like development, testing, and production.

2. Step 2: Identify the main use

   Switching settings easily means you can run the same app with different configurations without changing code.

3. Final Answer:

   To switch application settings easily for different environments -> Option A

4. Quick Check:

   Profiles = environment-specific settings [OK]

Hint: Profiles = different settings for different environments [OK]

Common Mistakes:

• Thinking profiles are for writing code
• Confusing profiles with UI design
• Believing profiles manage database manually

2. Which of the following is the correct way to name a Spring Boot properties file for a profile named dev?

easy

A. application-dev.properties

B. application.properties-dev

C. dev-application.properties

D. application_dev.properties

Solution

1. Step 1: Recall Spring Boot profile file naming

   Spring Boot expects profile-specific files named as application-{profile}.properties.

2. Step 2: Match the correct pattern

   For profile 'dev', the file should be application-dev.properties.

3. Final Answer:

   application-dev.properties -> Option A

4. Quick Check:

   Profile file = application-{profile}.properties [OK]

Hint: Profile files use dash between application and profile [OK]

Common Mistakes:

• Using underscore instead of dash
• Placing profile after .properties
• Starting filename with profile name

3. Given these files:
application.properties contains server.port=8080
application-prod.properties contains server.port=9090
And the active profile is set to prod, what port will the Spring Boot app run on?

medium

A. 8080

B. 9090

C. Both 8080 and 9090

D. No port will be set

Solution

1. Step 1: Understand profile override behavior

   Properties in profile-specific files override those in the default application.properties when the profile is active.

2. Step 2: Apply active profile 'prod'

   Since 'prod' is active, server.port=9090 from application-prod.properties overrides 8080.

3. Final Answer:

   9090 -> Option B

4. Quick Check:

   Active profile properties override default [OK]

Hint: Active profile settings override defaults [OK]

Common Mistakes:

• Assuming default always applies
• Thinking both ports run simultaneously
• Ignoring profile activation

4. You wrote spring.profiles.active=dev in application.properties, but your app still uses default settings. What is the likely problem?

medium

A. The dev profile is not supported by Spring Boot

B. You need to restart the app after changing profiles

C. The profile-specific file is named application_dev.properties instead of application-dev.properties

D. Profiles cannot be set in application.properties

Solution

1. Step 1: Check profile file naming

   Spring Boot requires profile files named with dash, not underscore.

2. Step 2: Identify mismatch

   If the file is named application_dev.properties, Spring Boot won't recognize it for profile 'dev'.

3. Final Answer:

   Incorrect profile file naming with underscore -> Option C

4. Quick Check:

   Profile file must use dash, not underscore [OK]

Hint: Use dash, not underscore, in profile filenames [OK]

Common Mistakes:

• Thinking profiles can't be set in application.properties
• Forgetting to restart app (usually needed but not main issue here)
• Believing 'dev' profile is unsupported

5. You want to activate the test profile without changing application.properties. Which of these is a valid way to do it when running your Spring Boot app from the command line?

hard

A. java -jar app.jar -profile test

B. java -jar app.jar -Dspring.profiles.active=test

C. java -jar app.jar --profile=test

D. java -jar app.jar --spring.profiles.active=test

Solution

1. Step 1: Recall command line profile activation syntax

   Spring Boot uses --spring.profiles.active=profile to activate profiles via command line arguments.

2. Step 2: Check each option

   java -jar app.jar --spring.profiles.active=test uses the correct Spring Boot command-line syntax. java -jar app.jar -Dspring.profiles.active=test incorrectly places the -D JVM argument after -jar; correct would be java -Dspring.profiles.active=test -jar app.jar. Flags like -profile test and --profile=test are not supported by Spring Boot.

3. Final Answer:

   java -jar app.jar --spring.profiles.active=test -> Option D

4. Quick Check:

   Use --spring.profiles.active=profile on command line [OK]

Hint: Use --spring.profiles.active=profile to activate profiles [OK]

Common Mistakes:

• Using -profile or --profile flags incorrectly
• Confusing JVM -D options without proper placement
• Trying to set profile inside application.properties only